Overview of the status of vector elimination projects

It AFRICAN PROGRAMME FOR ONCHOCERCIASIS CONTROL (APOC) ORIGINAL: FRENCH OVERVIEW OF THE STATUS OF VECTOR ELIMINATION PROJEGTS Prepared for APOC by Prof. S. Traoré Temporary AdvisorMHO/APOC t APRIL 2OO2 PLAN EXECUTTVE SUMMARY........... .................. t 1. TNTRODUCTTON .................... 1 2. NOTES ON ONCHOCERCIASIS lN AFRICA: VECTORS-DISEASE-CONTROL. 1 3. FOCI SELECTION CR1TER1A............ ....................4 4. PANORAMA OF SITUATION IN FOCI... 4. l. TUKUYU FOCUS................. 4.1 .l . Presentation of focus 4.1 .2. Nature of works 4. I .3. Results obtained 4.1.4. CDTI status in the Tukuyu focus......... 4.1 .5 . Budget for vector elimination activities 4.1 .6. Discussions - Remarks ................ 4.1 .7 . Conclusions-Suggestions .............. 4.2. BrOKO FOCUS.... 4.2-1. Nature of works.... 4.2.2. Outcomes obtained.... 4.2.3. CDTI status in the focus......... 4.2.4. Budget for vector elimination activities 4.2.5. Discussions - Remarks 4.2.6. Conclusions - Suggestions............. 4.3. ITWARA FOCUS 4.3.1 . Presentation of focus 4.3.2. Nature of Works 4.3.3. Results obtained 4.3.4. CDTI status in the Focus........ 4.3.5. Budget for vector elimination activities 4.3 .6. Discussions-Remarks 4.3 .7 . Conclusions-Suggestions .............. 4.4. FOCUS OF MPAMBA-NKUSI .............. 4.4.1. Presentation of focus 4.4.2. Nature of works 4.4.3. Results obtained 4.4.4. CDTI status in the Focus 4.4.5. Budget for vector elimination Activities... 4.4.6. Discussions-Remarks 4.4.7 . Conclusions-Suggestions .............. 5. OVERALL CONCLUSTON ....37 6. AKNOWLEDGEMENT 7. BIBLIOGRAPHICAL REFERENCES 4 4 4 5 5 ) I ............ t0 ............ 10 ............ 1t ............ 13 ............14 ............14 ............15 ............2t 22 22 24 26 26 27 27 29 29 30 30 32 32 32 33 34 35 35 36 38 39 t It EXECUTIVE SUMMARY I. INTRODUCTION In most of tropical Africa, human onchocerciasis or river blindness, a dermalfilariosis, caused by the parasite, Onchocerca volvulus, is still a serious public health problem. The parasite is transmitted to humans by the black fly, Simulium damnàsum s.l . The AfricanProgramme for Onchocerciasis Control (APOC) was established to control the disease through control of the parasite populations, in African Countries, outside the operational area of another onchocerciasis control organization, the Onchocerciasis Control programme (OCp) in West Africa. APOC's Strategy is Community Directed Treatment With lvermectin (CDTI).However, in some isolated foci at Tukuyu in Tanzania, Bioko in Equatorial Guinea, Itrvaia and Mpamba-Nkusi in Uganda, APOC has also initiated vector elimination activities duringthe past least three years. Following recommendations of a mid-term external review ofAPOC's Programme, principally, the action plan for phase II and a phasing out period, theManagement of APOC has decided to convene a meeting to critically .iri"* the vector elimination activities at all foci. As part of preparations foi the meetiné, *" provide here a synopsis of progress made at each of the vector elimination considered focus. 2. TUKUYU FOCUS The Tukuyu Focus located between the Tanzanian and the Malawian borders covers an area of about 3000km2. It is watered by three river basins: Kiwira, Mbaka, and Lufilyo. TheSongwe river, a main river bordering Malawi lies outside the focus. From WHO estimates in1995, about 650, 000 people in the focus have onchocerciasis; but the exact figures of endemicity are yet to be known through a survey. Ivermectin distribution started at the focusin 1994 and the CDTI, with a therapeutic coverage of 660/o, is going on satisfactorily. A synthesis report of Maegga (1991) indicated that between 1976 and 1997 several random transversal entomo-parasitological surveys were conducted in the Tukuyu focus. However,Since October 1998, the surveys have become regular with technical and financial ,uppo.tfrom the APoc programme. The results obtained are as follow: Breeding periodicity of Simulium: Studies conducted during the l9g0s and 1990s(involving Walsh & Maegga) agree with earlier ones, conducted in the 1970s and early 1980s (by Lebene and Guillet) that ; there are larval stages of Simulium stages of Siruuliunt damnosum s./ in the three major river syste.nr i, the Tukuyu focus. studies carried out by a national team during late 1998 and early 2oo2 revealed that; out of 85 breeding sites visited, simulidae were present at 46; 34 of which had S-damnosunt s.l. Observations made in 2002 also indicated that ZZ of 49 river breeding sites visited had aquatic developmental stages of Simulium while 9 out of 21 tributaries were also positive. Cytotaxonomic identification has confirmed that the Simulium c{amnosarrn species in the three main river systems within the Tukuyu focus is S.damnosum kiwira type(l 419 I 1479 Simulidae). Onchocerciasis transmission in the area has been indicated to occur during tlie dry seasoll based on occulrence on high populations of bitting females during the period. However, this observation must be treated cautiously b""ru." it is not certàin fly catchers have followed the standard protocol exactly. I ! uSensitivity of S.damnosum s.l at the Tukuyu focus to 2O%o temephos was put forward by Guillet (1981) and later confirmed by Barro (1999-2000). The LC95 has been determined to be 0.66 mÿl and 0.384mÿl îor low and high mortality rates respectively. Tests in rivers indicate that for a discharge of 4.3m3 /s and a dose of 0. I mg/l, the effective carry for (100% of déchrochement) of temephos was 7,060km. Bt had a maximum efficacy carry of one km. Analysis of annual distribution of simuliidae populations and density enabled Pederson and Maegga to conclude that tlie dry season (June-November) would be the ideal period for larviciding, as accessibility to breeding sites at that period would also be easier. The first ground larviciding took place between December 2001 and February 2002. The three main basins of the focus were subjected to a weekly larviciding using temephos at the dose of 1.33mÿl for 6 weeks. After the first week, no breeding site on the main rivers visited proved positive. Geographically, the natural barriers surrounding the focus (Lake Nyasa , mountains), initially, created the impression that the focus was isolated. Then in 1981, following a series of surveys including that of the Lumbira and Songwe rivers, Guillet concluded that the focus was not as isolated as previously considered. However, based on cytotaxonomical, entomological and epidemiological studies, the Tukuyu focus was declared isolated. Nonetheless, the data obtained in 1996 showed that ,S. damnosum s./. thrives downstream of river Songwe, the natural border between Tanzania and Malawi . Moreover, in the south west of the focus, a few kilometers from Lumbira, is the large and perennial river Kilando which could also harbour S. damnosum s. l. With the Kilondo and Songwe rivers located outside Tukuyu focus, it is not likely that the focus is isolated. Based on the different results, it could be deduced that tlre present distribution oî S danmosuru in the Tukuyu focus notably during low water level period is yet to be established. Some authors assert that the Tukuyu focus is isolated . Others, based on the proximity of the river Songwe and its tributaries and the presence of S. datnnsum s.l in some of them are cautious. It is therefore important to conduct an entomological re-assessment in the Songwe basin in Tanzania and Malawi. In addition, to accept or reject the hypothesis of potential reinvasion of the treated area by S.damnosurn from outside the focus, it would be necessary to undertake a vector identification in areas concerned. 3. THE BIOKO FOCUS The Bioko Island, a massive volcanic land covering20lT km2, is situated in the Gulf of Guinea off the coast of Cameroon and Gabon. Its watershed is made up of small rivers with Iow discharges which take their sources from mountains. The epidemiology of onchocerciasis is the forest type with an average prevalence rate of about 75oÂ. For CDTI, the target population is estimated at 60,000 people and the therapeutic coverage was 42Yo in the year 200 1. Studies on the onchocerciasis vector on the Bioko island starled in 1989. A TDR feasibility study on vector elimination in this focus was carried out in 1996. In 1999, various additional studies were conducted through APOC funding. The results obtained led to the following : - The southem part of the island, about 40% of total landarea is inaccessible. However, many surveys have been carried out in the accessible zone. The results indicate that the '5. darnrtosuttl complex is represented in the Bioko Island only by the Bioko form t a ? )ul oî S. yahense. The rivers are many, short (7km long on average) and protected by aluxurious vegetation, rendering the numerous rivers inaccessiÙlé. In tt " dry season, the discharges of the rivers generally fall below lm3/s and they are cleanind cool(turbidity < 5JTU) ; (l9oc<temperature<26oc) water. No piéimaginal stage ofS.damnosum was collected above 500m altitude, while, some aàult, *è.. captured at altitudes between 55Orn and 1250m. The authors were unanimous on the fact that the Bioko focus is isolated. In fact, it is an island where weather conditions including wind movement: have been considered to negate re-invasion of the focus. Additionally, cÿotaxonomical, morphological and cÿogenetical obviousnesses lead to the recognition of the fact that th; ^S. yihens" inBioko is different from the standard type. There is therefore a consideied genetic isolation compared to the known simuliidae species and those found à, tl.reCameroonian coasts. - It has been observed that apart from the dry season (January to April), the simuliidae population densities are not significant. On the contrary, MBR betwéen 1305 and l1 475 has been recorded in April- May and between 2970 and l0 380 in February. This means that even in the dry season , the simuliidae population density can be high. - In 1996 the dissection of 56 females helped to record up to 14.6% of infectious females. In 1999, the dissection of 878 femates revealed 44yo infected and gyo infectious females. Despite the fact that, the ATP has not be established for the year 2002' the MTP obtained in April and May at the various collection points *".. Àigh(MTP minimum :130 in Balacha; maximum : 473 at Musola ;. it tras also beenindicated that apart from collection points located at high altitudes (0<pMT<72), alt the others MTP are located between 319 at Sampaka and, lZ75 at Musola. Various studies of agree and indicate that transmission is significant on the Bioko Island. - Results recorded in 1989 and 1998 show that after 9 years of ivermectin treatment, prevalence has drastically changed from hyperendemicity (74.6%) to hypoendemicity(38.6%). Such a shift should be reflected by simulium infestation.'Thus, from 1993 to 2002, the number of infecting larvae for 1000 pares droped from 400 to 74 and MTpfrom 1600 to 15. However, the infestation rate recordedàuring 2001 does not seem tobe affected by the use of lvermectin: MTP between 319 i;Sampaka and 1275 at Musola. - The first ground larviciding compaign took place in Bioko during 2001 dry season. During the period of the exercise, only 30 rivers had enough watei flowing to enable treatment. Hence, out of 248 proposed treatment points selected, onlÿ 92 were retained. The selected insecticide for ground larviciding was temephos at the operational discharge dose of 0.4 litres/m3/s. The treatment, which lasted five weeks was carried out once a week from February l}'t',2001. From the numerous data collected, it can be retained : ' The carry of the insecticide was between I and 3 km for discharges ranging from 0.05m3/s to 0.2m3ls. I'hc life span of tlie preimaginal stage of Sirnuliurr was rather long (rnore than two weeks) becausc water temperatures were usually low ( from l9"C to 24"Ci. The recolonisation ofbreeding sites after each treatment was therefore very slow. t t lv Adult population density feel sharply after the commencement of the treatment. Fly catching was nil at some points after only four weeks of treatment, although rivers were not totally treated. At the structured operational dosage, the number of chironomides was reduced however, repopulation was relatively fast. On the other hand, fish and shrimp populations were not undurely affected ( no mortality, normal behaviour ) by the larviciding. At the end of the first exercise which took place in the north of the island, expert consideration indicated that due to inaccessibiliÿ of some rivers, ground larviciding alone cannot eliminate the vector from the Bioko focus. This objective could however, be achieved in a one single season through combined ground and aerial larviciding. However, as authorities stated, the use of helicopter for the exercise should be indicated by proper answers to some questions. Such as : what is the impact of twelve years of ivermectin distribution on the simulium capacity to transmit the disease? What is the cost of the aerial operation advocated ? How many people will be protected through this operation? Reference to the target objective, which is to eliminate the vector, various results obtained in Bioko, indicate the following : The geographical location, weather conditions and cÿotaxonomical, morphological and cÿogenetic criteria confirm that the Bioko Island is isolated. Based on the distribution of the rivers and prospected breeding sites, it is evident that each survey, would reveal at least a new breeding site (discovered in a river already itemized or not). Moreover, the presence of the adult vector in high altitude is a reinvasion risk factor for a treated zone. This situation impedes the total coverage of breeding sites by through larvicidings as a must for the vector elimination. 4. Itwara Focus At about 25 km north of Forte Portal, Iies the Itwara focus surrounding a forest reserve that bears the same name. Hydrological conditions are generally conducive all year round for the development of the Pré-imaginal stages of S. neavei. The breeding sites are mainly located on rivers Sogohi, Siisa and Aswa. Onchocerciasis is highly endemic in that densely populated zoîe. The Itwara focus community and its sub-foci (Siisa, Aswa) are isolated from the other onchocerciasis foci. The nearest focus being about 100km away and mostly infested by S neavei whose flyrng range does not exceed 10 km (Garms, 1997.) ln the 1970s, the use of DDT, emulsifiable concentrate at 25o of active ingredient disrupted the transmission of onchocerciasis in the ltwara focus (Garms et al., 1994). Due to lack of funds and insecurity, the control was interrupted from 197 5 to 1977 . However, in 1990, a new funding jointly provided by the German Cooperation Agency (GTZ) and the Ugandan Ministry of Health made it possible for data collection to continue. In this connection, all the rivers likely to harbour S. neat'ei s.s were surveyed and the adult population of S. neavei studied through fly catchings, dissections and determination of infestation rates.'fhe larviciding of temeplios carried out from August 1995, proved to be effective with promising results after only three larviciding cycles. In fact, between I994 and i i a Iv 1995, the simulidae density dropped from 481 to 0 at the Kijura bridge and from 365 to 2 atBusasa. Considering the results obtained, larviciding were extended to the major breeding sites for S. neavei in the focus. The entomological data collected between 1991 and 1994 prior to the treatment withtemephos indicate that38.90 of crabs captured in the river Sogohi 1lt*u.u focus) carried thepréimaginal stages of S. neavei. Results of various surveys tally and show that treatment of breeding sites withtemephos drastically reduced the S. neavei preimaginal population irrespective of the focus orits sub-focus (Siisa, and Aswa). Even when treatments weie discontinuàd, low densities were recorded' Post-treatment controls in the Itwara focus revealed that since i997, infested crabs are nearly absent. The same is true, since year 2oo}, in the Siisa sub-focus. Be'rween January and August 2001, surveys conducted by the national team have made it possible to catch 4656 crabs in the Itwara focus, with the breakdown as follows: 948 in Itrvara, 630 in the Siisa sub-focus and 3078 in Aswa sub-focus. No préimaginal stage was discovered on the crabs fromItwara. Only a larvae was detected on on. "rib 1i.e. o.zN of population) from Siisa. Thehighest percentage (0.4%) of crabs showing positive were noticedin Aswa. ' From the beginning of treatments in 1995, the S. neavei population density hasdropped, reaching the zero mark in 1996 atKijura and Sogohi. As the tàatment went on, thetendency has intensifted because no biting female *"r "uptu. ed in ZOO2 in the entire focus(ltwara, Siisa, Aswa). Results recorded in 2001 confirmed the absence of bitint females in the zone' It is worthy to note that prior to the treatment with larvicides, the simuliidae populationdensity was 19,000 bites per person and per year. With the current situation, vector elimination activities in the Itwara focus and its sub-foci (Siisa, Aswa) can be called a success. It is likely that children bom since the beginning of operations would no longer be carriers of the micro-filaria. However, ivermectin distribution should continue due to the longevity of the adult O. volvulus worïns carried by old patients. 5. The Mpamba -Nkusi Focus The concemed vector elimination area, covering a landarea of 100 km2 lies in theNorthern part of the Kibaale District. The district is madi up of 3 prefectures but it is only inBuyaga prefecture that onchocerciasis is endermic. The population at risk is about at 70 000with a prevalence rate between 58o and 80%. Therapeuiic coverage was 74yo in 2001 in theKibale District. Perennial rivers with breeding sites fàr S. neavei all the year round constitutethe hydrography of the focus. During surveys for larvae carried out in Lgg9,28 (41%) crabs out of 6gg were carriers of S' neavei Pre-imaginal stages. The same data for the yeàrs 2000 and 2001 were respectively s06t 623 (8 1 %) and 393 t 642 (s3.4%). Characteristics of female vectors recorded at Sioni were as follows: 33.9% pares; 14.7oÂinfected, 2-7o infectious; MPT from 13 lo 50 Lil1000 pares. At Rurembo,26.50 pares20A% infected,0.6% infectious,2lLil1000 pares and PüT value of 2g were obtained. AtNyabugando, transmission rates were'. 27,8o/o ienrelles pares, 18.3% infected pares, 6l Lil1000pares and a PMT value of 86.2%. A pilot treatment exercise was carried out on Mpamba river ip November 2000. This rcduced tlie infestation rate of crabs tiving in the river lronr about 66,1yo to 92.50Â. VI The same was true for crabs confined in experimental cages and placed at river beds where reduction rate ranged between 98.5% and 100%. S.damnosum and other simulidae breeding sites were all negative after larviciding. The non-targetted fauna (trichopterre, bloodsuckers, water scarabs) were not affected. During the experiment, the dischaige of Mpanrba river was 1126m3/s, with water temperature reading lg.2"C and insecticide-carry estimated at 5km. The experimental treatment carried out in 2001 on Mushandikwu ,nà Rwabutuji rivers also showed a drastic reduction in crab infestation (100% mortality rate over 2km.). To conclude, the following must be noted ; Sampling conducted indicates that the simulium flies in the Mpamba- Nkusi focus are ,s. neavei and S damnoswn, Nkusi type. Even though considered non_ anthropophile, the latter species' characteristics and its vector status must be well- defined. The biology of S neavet, success chalked by the experimental larviciding, extent of the focus, ecological and geographical isolation of the focus and the all-weather accessibility to rivers are factors indicating that the vector elimination exercise in Mpamba-Nkusi focus can be carried out with good chances for success. The problem of insecurity which, at any moment could slow down or even impede the conduct of anti vectoral activities is yet to be solved. Despite the efficiency of larviciding and probable etimination of the vector from the Mpamba-Nkusi focus, Ivermectin distribution should continue considering the longevity of the adult O volvulus worrns present in previously infected persons. GENERAL CONCLUSION The presentations on vector elimination in different foci of Tanzania, Equatorial Guinea and Uganda provided the opportunity for assessing the progress made in each project. It is very clear that the projects were implemented on the basis of factors such as focus iize, its isolation and the availability of baseline data. However, project feasibility was not given enough consideration and some factors (actual limits of the focus, accessibility to breeding sites, reinvasion risks) were sometimes underestimated. With the S neavei vector, the factors enumerated above do not always pose problems due to the bio-ecology of the vector. However, with .ÿ damnosum s. /., the limiting factors keep on increasing: many supports, difficult accessibility to all breeding sites, generally high simulidae population densities, high flying capacity. Total coverage of breeding sites is a sine qua non condition for the vector elimination. Moreover, it was understood that in the selected foci vector elimination would be complete, definitive and fast. This objective remains achievable in the Itwara and Mpamba-Nkusi foci. On the contrary, what actually comes lrom the field compels us to admit that the vector elimination in the Tukuyu and Bioko foci could have been a very ambitious objective. We should be mindlul of one of the recommendations of JAF6 that if the meeting decides to stop the vector elimination activities in the focus, recommendations should be made to the countries concerned to enablc tliem to continue fighting the vector in a national or bilateral(cooperatiott) context. In thc case where activities should be pursued, some conveniept arrangenlellts sllould be taken at the APOC level to execute, supervise and evaluate the larviciding activities. t ! 1. INTRODUCTION onchocerciasis is a human disease caused by a nematode filarial worrn, onchocerca volvulus,transmitted to man by the Black Fly Simulium. 'Ihe disease which is manifested by skin lesions, visual imperment and blindness is still a major public health problem in most part of tropical Africa.As at 1996, this endemic disease affected 17,5 million people, out of whom tS mittion (gSyr) lived in countries outside the Onchocerciasis Control Programme (OCP) area in West Africa. The AfricanProgramme for Onchocerciasis Conhol (APOC) was therefore designed to control this criticalparasitosis in regions that were not covered by the OCp. The overall objective of onchocerciasis control is, usually, being able and in a sustainable manner' control the endemic disease, though the final objective set by APôC is the elimination of thcdisease, as a serious public health problem, and an obstacle to socio-èconomic develofment in Africa.The strategy adopted is the Communiÿ-Directed Distribution of [vermectin (CDTI). However, since the launching of APOC, vector elimination projects have underpinned theCDTI in some countries. These projects, which are approved by ihe-Committee of Sponsoring Agencies (CSA) and ratified by the Joint Action Iorum (JAF), are ongoing in Uganda (in the foci ofItwara and Mpamba-Nkusi), Tanzania (foci of Tukuyu), and in Equatoàat Cui.,"u"1foci of Bioko). The control strategy applied in all these foci has been control of pàpulations of thè disease vector byground larviciding aimed at elimination of the vector, and consequently the disease. The APOC programme undertook these vector elimination activities on the basis of elements such as the size and extent of isolation of foci, base data available, and the cost of operational campaigns. Besides, it could be said that this ÿpe of control has several positive aspects: rapidintemrption of transmission, no consequences for the environment, and in principle, and the definite nature of control effects. At the outset, therefore, the understanding was tirat th! eiimination of the vector in the foci would be total, definite and fast. The acceptance and financing by the APOC progmmme of the various vector eliminationprojects were spread between 1996 and 1998. To date, at leàst three years have elapsed, and it is worthknowing where these projects stand. This concem was expressed in 2000 by thË faÉO lf.ogrammeexternal review), which, in one of its recommendations, authorized the manage-"n, of ApOC to organize a meeting charged to determine the Programme strategy for vector efmination fo. tt e ziùphase of the said activities. This meeting was to call on all the expertise (namely, participating countries, APOC OCP, TDR, TCC and all resource persons). Besides, in the àir"r..-io.,., particular attention would be accorded to the impact of ivermectin (CDTI, CBTI)) on the epidemiology andtransmission of onchocerciasis. The JAFT came to determine that no new vector elimination lioiectwould be undertaken during phase 2, and during the withdrawal phase of APOC. It also confirmed that the current activities would be cntically reviewed at the beginning of phase 2, in order to decide on the continuation of the projects. In line with the recommendations made after the mid-term External Review of the APOCProgramme, as well as on the basis of the Plan of Action for phase 2 and the gradual withdrawal ofAPOC, management decided to hold the vector eliminatron review meeting in ApOC countries in May2002' It is, therefore, wtth respect to the preparations for the said meeting, that this surrrmary tries to note the progress made, since the start-up of activities in each of the foci. 2. NOTES oN ONCHOCERCTASIS rN AFRICA: VECTORS-DISEASE- CONTROI,. The disashous consequences of ocular signs of the onchocerciasis disease are well known.However, unttl recently the suffering caused by skin lesions, due to onchocerciasis, and the attendantintolerable Itching had been under esttmated. It is asserted today that onchodermite refresents a heavy 2burden and that its manifestations bring about serious psychological repercussions, not only on patients, but also on their families and communities. In addition, the itching is the most painful effect of the onchodermite. [n some communities, however, 80% of the population suffers from this affectron. In Africa, the onchocerciasis vectors that are known are Similium species complexes (S.danutosunt complex, S. neavei group, and the S. albivirgulotum group). In the peculiar case of Central and East Africa, the following could be noted: The vectors of the S. damnosurtt complex have tendency of confining themselves to areas that are surrounded by either non-anthropophilous black fly populations, or in ecosystems that don't suit them. The species, therefore become "stationary". As they generally reproduce in big watercourses, their breeding sites are relatrvely accessible for larviciding. Punctual operations of vector control could, therefore, be carried out in these foci, with a good cost- effectrve ratio. ln several foci, the vector found is the S. neavei, the species that require the presence of fresh water crabs, which the pre-imago stages use as support. Because of this, the §. neavei population does not generally attain the high densities that characterize the S. damnosum. In addition, the bibliographic data indicate that this group of species has problems in reconstituting its populations when they are greatly reduced. Until 1987, onchocerciasis control in West Africa was solely based on vector control. The latter continues to be the mainstay of control, but with the advent of ivermectin, there is a new tool that has radically changed the control strategies. The latter are mostly determined on the one hand, by the geographical location of pathologies, and on the other, by the existence, efficacy and cost of intervention tools, which are as follows: lvermectin, which is a microfilaricide, administered orally to man; Vector control: thanks to insecticide spraying, this method enables the transmission sequence to be broken, by destroying the vector at the most vulnerable stage, i.e. the larva stage. The frequency of treatment depends on the duration of development of the pre-imago stages, and especrally the time that separates the hatching of larvae from their nymph stage. In the OCP area, the control of the disease was essentially based on vector control. In APOC zone, this strategy often proves to be technically impossible or less profitable. It is for this reason that the main method used by APOC is the communrÿ-based distnbution of ivermectin. However, in some rsolated foci, it has been decided to undertake vector elimination. ln West Africa, there are no cases of onchocerciasis vector elimination, for the black flies of the S. dmnosunt complex move over long distances. On the contrary, in East Africa, the use of ground treatment of larvae breeding sites has enabled the elimination of vectors in six small foci, found in Kenya (Mc Mahon et al, 1958), in the Democratic Republic of Congo (Walsh, 1990), and in Uganda (Prentice, 1974). This success indicates that a vector elimination operation could be undertaken in any focus that has similar characteristics as these six foci. Expenence has shown that smaller-scale operations, which don't conveniently cover the entrre focus, may, nevertheless have palpable effects on the S. neavei vectors, if they are continued over several months or if they are carried out intermittently over 6 to 8-month cycles. In these S. neavei foci, eliminatron is the solutton to the onchocerciasis problem. The latter is so advantageous that: Risks of resrstance and environmental degradation are low; Costs of insecticides are reduced, since control is rntermittent 'fhc fact of regularly ustng insecticides is a potential nsk factor to the aquatic environment. [n vtew of thrs rrsk, a lot of attention needs to be paid to the surveillance protocol of the aquatic environment, and to the choice of larvrcide. This choice is linked to the product (cost-effective ratro, toxrcity for non-target fauna, formulation characteristics), to the watercourse (hydrologrcal pattem, 3characteristics of breeding site), and to the black fly population present (level of sensitiüÿ to the recommended product). Whichever insecticide used, the concentraiions must be imperatively have a100% lethal effect on the black fly larvae population, through the insecticide, and aiegligible and/or zero effect on non-target fauna. with respect to ground treatment, various works have shown very good performances ofTemephos, with an active matter of 20%o emulsifiable concentrate. It is an organophosphorous biodegradable compound, with no toxic effects on mammals and fish. Its impact Ànîon-tu.get faunais moderate. In addition, OCP experience helps to know that the Bacillus tlruringiensis I{14 (Bt) could equally be used. This product is a biological insecticide. It is to be noted that an error of appreciation in the quantity of insecticide to be sprayed may have multiple repercussions on a vector control programme. In the event of overdose, the srirplus insecticide consumption has senous financial and/or ecological consequences, if the chemical u.àd i, expensive or relatively toxic. on the contrary, overdose may, on the one hand, favour the apfearance of resistantblack fly populations, and on the other hand, cause an increase in biting.ates, anàïen"" un increase intransmission. That is why a hydro biological surveillance netrvork ,nrri b" pri i1 place at thebeginning of the Programme on all the treated rivers. The impacts of the insecticide teatment on the vector populations and parasite transmission are appraised through entomological evaluation. The latter starts prior to control operations, through a complete inventory of larvae breeding sites, and the collection àf b"." data on thl identity of spiiesof the complex, the rate of bites and transmission potentials. During the operations, entomological surveillance makes it possible to detect a sizeable local production if blact flies, àL" ,o trearment Iapses or to resistance, and to detect an exogenous input of vectors. Treatment maÿ, then, be reduced or stopped in the regions where there are no black flies. By enabling the verification of the efficacy oftreatment at the pre-imago (prospecting of rivers) and imago stages (capture, identification, disseciion of females), entomological evaluation constitutes the mainslay oith" cont ol operations. Data collected during the entomological evaluation allows for the establishment of entomological indices of transmission, which are the Annual Biting Rates (ABR), and the Annual TransmissionPotential (ATP). They quantify black fly aggression and parasite transmission respectively for a subject placed at a given point, because it is representative of the most dangerous situation thatprevatls in the region. The ABR and ATP are good comparative indicators àr tn. entomological situation. They usually constitute the basis of evaluation of thà vector control results. 43. FOCI SELECTION CRTTERIA Vector elimination can only be undertaken in a focus that has a number of criteria The focus must be isolated (not at the mercy of re-invasion by exogenous black flies). The vector must be identified in order to adapt control to the species. The vector elimination activity must be easy to manage, and must guarantee a quick investment turnover for an increase in productiviÿ, and a reduction, in the long term, in the need for CDTI. 4. PANORAMA OF SITUATION IN FOCI 4.1. TUKUYU FOCUS The bibliographic data on onchocerciasis in the Tukuyu focus are relatively abundant: FISHER (1932), HAWKING (1940), Anonymous (1976, 1977), LE BERRE (tgzg), wALSH et al(1981), PEDERSON and MAEGGA (1985), V/ALSH et al (1985), PEDERSON and LOLSTROp (1986), MAEGGA (1992), MAEGGA and CUPP (1993, 1994), WALSH and MAEGGA (1996). The authors especially dwelt on the entomological, epidemiological, cytotaxonomic components, and vector control, using insecticides. These different works help to characterize this focus. 4.1.1. Presentation of focus The focus of Tukuyu (fig 1), located at the frontier between Tanzania and Malawi, spans an area of about 3,000 sq km. The region under review is found between 905 - 9045 of West longitude and 33020 - 34024 of West latitude. It extends from Lake Nyasa (south) to the Volcanic Mountains in the north and has to do with two districts (Runge, Kyela), two administrative regions (Mbeya region, Iringa region). The focus, thus demarcated, was declared isolated, since it is surrounded by natural barriers, namely Lake Nyasa and the surrounding mountains (Livingstone, Rungwe, Umalila, Undali, Mporoto). The climate rn the region is characterized by a dry season (June-October), and a rainy season(November - May). However, rainfall is all year round, with the peak in March, April and May (fig. 2, 3, 4). Rainfall figures in some areas are regularly around 2,000 mm per annum (fig. 5). The weather is relatively cold at the summit of the mountains (average 60C). On the other hand, in the plains, the weather is hot and humid all year round. This situation is due to the mountains, which annuls the influence of seasonal winds. The focus of Tukuyu is watered by three river basins, whose main watercourses are the Kiwira, the Mbaka and the Lufilyo. They take their source at a high altitude (2,400 - 2, 800 m) on Mount Rungwe. Then they descend to the plains, flowing over the slopes of the mountain, creating of rapids and favourable conditions (especrally in the dry season) for the installation of pre-imago stages of S. damnosum s.l. On their way, the Kiwira and the Lufilyo receive some tnbutaries (Luswisr, Mwalisi, Rumakali) from other mountains (Mporoto, Undali, Kipengere, Livingstone). Songwe, located in the west, and outside the focus, is a watercourse on the frontrer rvrth Malawi. Vegetation varies from savanna to dense forest and degraded forest. The latter covers the largest part of the Tukuyu focus, with Savanna and dense forests covering the slopes of the mountains. Thc populatton of the zone under study is broken into the drstncts of Kyela and Rungu,e, whrch have thc hrghest human population figure in the focus (about 69 rnhabitants/sq km). The ma;ority of inhabitants are engaged in intensive agriculture, which rs undertaken on fertile volcanic soil. The forest has, partly, been cleared for agro-industrial plantations (tea, coffee, cocoa, banana. 5rice, cane sugar), and for market garden produce and fruit (tomatoes, mangoes, pears, oranges). Fishing is undertaken along the watercourse and on Lake Nyasa by some of the ùhabitants. The identification works of PDERSON and MAEGGA (1985) and of MAEGGA and CUpp(1993, 1994) indicate that the black flies that are responsible for transmission in the focus of Tukuyu belong to the S- damnosum complex. It is, specifically, the S. damnosum, Kiwira ÿpe. The other blackflies found in the area are the S. nyasalandicum and S. bovis. Thc highest onchocerciasis prevalence rate (62.8%) was recorded at Kilugu, a village located at an altitude of 760 m on the Lufilyo. The human settlements upstream or downstreu* àf Kuluguhave much lower prevalence rates (20 to 5l%). In the entire zone, skin lesions are severe, and constitute the real onchocerciasis problem. With respect to prevalence, the area has been covered by the of rvcrmectin distribution programme, since July 1994. 4.1.2. Nature of works Several ad hoc surveys were carried out in during lg76-tgg7the Tukuyu focus prior to the start-up of APOC activities. The summary of them indicates that they dwelt on the followin!: - The determination and distribution of levels of endemicity; - The location Simulium breeding sites; - The identification of vectors; - The dynamics of pre-imago populations; - The dynamics of adult populations; - The behaviour of adult populations (namely, the rate of aggressiveness) - The vector characteristics of females of the S. damnosum (rate of parnr.ition, infestation ofblack flies, transmission of onchocerciasis) ; - The determination of the duration of larvae life; - The feasibiliry of vector elimination activities. The protocol approved by APOC in 1996 also made provision for the follorving: - The location of main breeding sites, namely those found at a high altitude; - The collection of larvae of the §. danmosums./. in the Carnoy on an positive breeding site; - The capture and dissection of black flies coming from pre-selection points (Lufilyo crater on the Lufilyo river, Lwanga Masoko on lower Krwiri, Tapio Bridge on the lower Lufilyo, and Kambasegela on the Mbaka); - The collection of rainfall and hydrological data; - Training of personnel. Finally, for the elimination of the oncho vector in the Tukuyu focus, the spraying of Temephos, as an anti-black fly larvicide, was recommended. Before any operation, u ir*"/will have to be conducted to: - Determine the actual impact of Temephos; - Measure the sensibilrÿ of the larvae of the ^s. damnosurtt s./. to Temephos; - Train local personnel on the management of nver trials and sensibility tesis 4.1.3. Results obtained The presentation of outcomes takes account of the data collection period, erther before or after thebegrnning of APoc activities rn rhe focus. This distinctron should enable: - The apprarsal of elements that allowed APOC to engage in vector elimination activrtres rnTukuyu; - stocktaking of the progress made in vector elimination in the focus. I; t Ii I 6 4.1.3.1. Data collected prior to APOC a) Prospccting breeding sites ln the 1970s and 80s, the pre-imago stages of the S. damnosuttt s./. were harvest in the dry and wet seasons on the Kiwira, Mbaka and Lufilyo rivers (Le Berre, 1970; Guillet, lggl; WalshLt al, r98r, l98s). The works of Pederson and Maegga (1985), then Walsh and Maegga (1996) confirm that thelarvae breeding sites of the S. damnosutn s.l. exist in the Tukuyu focus. fn tnè dry and rainy season, the three main rivers (Kiwira, Mbaka, Lufilyo) and some tributaries shelter pre-imago stages of the S. donurosurtt s./. The production of black flies is, nevertheless, the most important in ilw water periods, and on breeding sites at mid-altitudes (600-700m). Dispersron is important in the rainy season. On the contrary, in the dry season, the productive breeding sites are located on the middle tou..", of major rivers. ln addition to the latter, the Songwe River and its tributary (the Mwati), shelter some pre-imago stages of the S. damnosum s./. during the dry season. The same goes for the Lumbira River, whoielower course is an important source of black flies (§. damnosum s./., especially), due to the high number of breeding sites. The cytotaxonomic identification (Maegga, 1992;Maegga and CUPp, 1993, 1994) indicateD that the S. damnosum species, which lays its eggs in the main three rivers of the Tukuyu focus is the s. danutosum, the Kiwira ÿpe.kr actual fact, out of the 970 identified larvae, 910 (about 94%) were of the S. damnosum, Kiwira type. Besides, 509 larvae from the hatching of eggs laid by 7'0 gorged females on captors, were all identified as being of the Kiwira spe. Thrs vectàiis different fràrnite other ÿpes of the .S. datnnosum found in the neighbouring foci. b) Captures-dissection-transmission. Between 1979 and 1981, adult captures for determining the activity cycle of the S. damnosttnt s./., and for specifying the vector characteristics, were carried out on 9 sites, spread over the Tukuyu focus. In each of these points, two consecutive days of capture took place every two weeks, i.e. 4 days per month. The capture was spread over the whole day. Dissection of these flies and the search for O. volvulus helps to determine that onchocerciasis transmission was mainly a dry season transmission(low-water period), due to the high density of biting females, and to their beit contact with human populations. This was partrcularly high near villages of high prevalence. The rainfall figure-temperature-biting rate correlation was confirmed in a study conducted in 1987 and 1988 on four of the nine previous sites. It indicates that the ABRs were low, and did not go beyond 20,000, except on the middle course of the Lufilyo. The highest black fly densities in the dny season were obtained at between 500 and 800 m altitrude. The rates of parturition were low (22%o), and ATP was generally lower than 1,000. On the conhary, the rate of infective parous females *ui nign(38.3%). Pederson and Maegga (1985), after examrning a population of 19,500 of the S. damnosum, Kiwira §pe, confirmed that the annual biting rate fluctuated between 2,000 and 23,800. The dissection of 13,200 females (68% of capture) enabled 7.6%o of infected ones, 1.5%o of infecttve ones, and an ATP fluctuating between 0 and 1120 to be recorded. The latter rate was observed in an area, where the average prevalence of carriers of microfilaria was 54.60/0. At the end of this study, the authors confirmed that transmisslon was a dry season phenomenon. c) Larvicide treatment Bascd on cxperiences from the Kenyan and Ugandan foci, Walsh, in 1990 indicated that it was technrcally possible, ustng tnsectrcide treatment, to elimrnate the vectors (5. damnosunt s.l. and.S. treavei), from the onchocerciasis foci of Tanzania. The cost of such operations would, to a large extent, depcnd on the nature of thc tcrratn and on thc srze ol the larvae breeding sites of each focus. a 7Given the very'' gôod performances of the Temephos, with an active matter of 20oÂemulsifiable concentrate, it was recommended for ground treatment in the Tukuyu focus. Thisinsecticide was successfully used in several foci (eipecially Sogohi in uguna"J, but was neverexperimentcd in Tukuyu. However, Guillet (1981) indicateditrut À. sensibil"§ orirr" larvae in thisfocus was normal. In addition, the duration of pre-imago laboratory developm-ent (egg - adult) was190.5-210c, (three weeks), with two weeks being for the duration of larvae tire. on Àe contrary, the various field tests for determining the duration separating egg laying from adult hatching were notpositive. The operational efficacy of Temephos in the Tukuyu focus was estimated, taking into accountthe expenence acquired with oCP (Walsh, 1985; wash Ét al, l98l; Kurtak, lgsoy, and the results obtained in westem uganda (Garms et al, 1986). Thus, under the hydrological conditions of Tukuyu, it was established that the doses to be sprayed would be 0.33 I and 0.4 l/m3 lespectively ior output higher and lower than l0 m3/s. With respect to the period of treatment, the analysis of annual distribution of black flydensities enabled Pederson and Maegga (1985) to decide thai the dry season 11r". io November) wasthe period when access to the breeding sites is easiest. Besides, the flow rate of watercourses isregularly low and gradual, a larvae breeding sites are confined to some places of the watercourse. Forthese reasons, it was decided that insecticide teatments would take place in the dry season. Eachbreeding site would be teated every two weeks, and in principle,8 trlatmenf "y"t.. .p."ad over 16weeks, should be enough for eliminating the vector. As fàr the spraying points, u a.tuitéa prospecting of the main rivers and their tributaries enabled a selection of 26 oithem. - d) Prevalence The first report on onchocerciasis in Tanzaniahad to do with the Tukuyu focus (Fishe r, 1932).Hawkig (1940) confirms the presence of onchocerciasis in the focus. The distribution of this disease was, therefore, established gradually (woodruff, 1965, wHo 1966; wegesa, 1970). ln 1995, wHo estimated the number of people affected to be 650,000, but the exact extent of the endemic disease remained to be determined through investigations. Granback (1913) determined that640 of the 260 people that were examined in the village ofLufilyo were carriers of the o. Volvulus microfilaria. pedè.son and Kolstrop (r9g6j examined 2,349people aged between I and above. This sample, coming from 2l villages,i.'r.al.â that the highestprevalence rate of 62.8%o was recorde d at 7 60 m altitude ln the village oifritrgu. rn. iutt". is located on the middle course of the Lufilyo. In the other 20 villages, prevalence fluctuated between 20T and5l%' Dermatological affections constitute-the. most criticai problem, for even lorv parasitic loads cause lesions in some patients. And yet Mwaiko et al (1990) estimated that about 120,000 people were affected by onchocerciasis in the focus. Ivermectin distribution started in 1994, and until 1998, 20,000, 25,000, 40,000 and 42,000persons had benefited from treatment. d) Isolation of the Tukuyu focus The geographical siting of the focus, surrounded by natural barriers (Lake Nyasa, mountains), naturally led to the idea that the focus was isolated. This peculiar sihration, if verified, would make vector elimination feasible. In 1981, following a series of prospecting, includrng that of rivers Lunrbila and Songrvc.Gurllct concluded that the focus was not as rsolated as thc geographical environment made it look.Conseqrrently, vector elimination became hypothetical Cytotaxonomic studies (Maegga, 1992; Maegga and CUpp, 1993 and 1994) waived thedoubts of Guillet (1981) as to the isolatton of the Tukuÿ, fo.ur. In effect, apart from the s. dtnrto.strttt, 3 8Kiwira t)Pe, no other cytoÿpe could immigrate into the focus. In other words, from the cytotaxonomic point of view, this was an isolated focus, which only contains the S. damnos;u,n, Kiwira ÿpe species. The extent of isolation is, however, very high, otherwise only one ÿpe would not be so predominant in the area. It is therefore, on the basis of these works, the entomological studies (pederson and Maegga, 1985) and epidemiological studies (Pederson and Kolstrop, 1986) that the Tuduyu focus was dectààd isolated. Vector elimination of the said focus could be undertaken with success (Walsh and Maegga, 1996). 4.1.3.2. Data collected after the start-up of APoc activities a) Prospecting breeding sites This was mostly done by the national team. Between October and December 1998, the productiviry of breeding sites of the main rivers(Kiwira, Mbaka, Lufilyo) was regularly monitored. This study aimed at determining the upper limit(altitude) of the distribution of pre-imago stages (fig.6).Thus,31 breeding sites were geo-rllerenced and prospected for harvesting pre-imago stages in the regions of Mbeya (Rungwe, §ela, lleye,Mbarali), lringa (Ludewa) and Rukwa (Sumbawanga, Mbeya). Out of l8 positive breeding sites, only 9 shelter the S. damnosum s.l. In the districts of Rungwe and Kyela, only a breeding site was found tô be positive, out ofthe 17 prospected. In September-October of 1999, the S. damnosurn s.l. was found in the entire breeding sites(13) on the main rivers (10 breeding sites), and on some tributaries (3 breeding sites). Therà was, however, some dispariÿ between the plethoric imago population and the scarcity of pre-imago population in the breeding sites. In 1999, 24 breeding sites were prospected and 14 were found to shelter larvae and/or nymphs of the S. damnosum s./. All the positive breeding sites were geo-referenced, and larvae were sampled in the Camoy. This activity continued in February 2000 when two breeding sites were found to be positive, out of the 11 prospected. Between July and September 2000, the prospecting undertaken by Barro, apart from the pre- established limits (Walsh and Maegga,1996), made it possible to visit 28 breeding sites, l3 of which were positive on the main watercourses (Kiwira, Mbaka, Lufilyo). In addition, out of the 2l breeding sites prospected on the tributaries, 9 sheltered pre-imago stages of the S. danmosum s.l. From the altitude point of view, the distribution of the S. damnosutn s.1., was between 412 m and 1,000 m approximately. This distribution was variable, depending on the river basins. b) Captures-Dissection-Transmission These activities were carried out by the national team. The analysis of capture and dissection sheets indicate that the captors did not generally apply the usual standards for capturing black flies(Barro, 2001). The following results are therefore to be considered with caution. Between October and December 1998, a day of capture per month, was undertaken at Tapio and Kambasegela, as against two days at Luhlyo-crater and Lwangwa-Masako. These capture points tally with the various levels of prevalence in the area that is under treatment with ivermectin. Thus, 225 females were captured and dissected. These dissections enabled the recording of 99 parous females (44%),19 infected (19%) and 7 infective females (7%). Between January and December 1999, tables 1,2,3 and 4 indicate that 144 days of capture enablcd a harvest of 1,362 females at Lufilyo-Crater (499 females), Lwangwa-Masako (635), Tàpio- Brrdge (149) and Kambasegela (79). The dissection of 1357 females revealed 390 parous femàles(28.7%),40 infected (10.2%) and 3 infectlve ones (0.76%). The ATP was 83, for MTp was 23 in June, 60 in August and zero for the other ten months. The average black fly density was 9 bites/man/day, but e t -v 9 taking into account a distribution per capture point, it was 3, 13 and 6 at Kambasegela, Lufi lyo-Crater,Lwangwo-Masako and Tapio-Bridge respectively. The entomological evaluation undertaken between January and December 2000 (tables 5,6,7 and 8) indicate than in 144 days, 6240 females were captured at Lwangwa-Masako ( I 815), Taplo n.iage(1893), Kambasegela (300), and Lufilyo-crater (2230). out of these females, szjo were dissected, ofwhrch 176l were parous (30.5%), 144 infected (8%), and l8 infective (lyo). The MBR flu*uatedbetween 8 and 3930,465 and 3810,30 and 1695, and between 98 and 3068 àt Lwangwa-Masako, Tapio-Bridge, Kamasegela and Lyfilyo-crater respectively. For these same capture points, the MTp was nil forsix months of the year: January, February, March, April, May and November. In 2001, 9923 females were captured in the Tukuyu focus (fig. 7). The average densiÿ was 4gbites/man/day. Besides, females were more abundant on the Lufilyo (66 bites/maiday;, then on theKiwira (38 bites/man/day), and finally on the Mbaka (14 bites/mar/day). For these same watercourses, the MBR fluctuated between 430 and 5880, between 38 and 4073 andbetween l5 and 2550 respectively.Data on dissection are not available. c) Larvicide treatment The sensibiliÿ tests, river trials and the first ground treatment of the focus were entirely carriedout by the OCP team under Mr. Barro. It is worth noting that the national team took part in these operations- An APOC employee also participated in this first ground treatment operation. The sensibiliÿ tests that were carried out in October 1999 indicate that the larvae were subjectedto a series of concentations: 0.00975 mÿL0.039 mg/I,0.156 mg/l, 0.3125/1,0.625 mg/|,1.25 mÿl and2-5 mgfl- At a temperature of 2O-22o.C, mortaliÿ rates of 5O%, gO% and 100% weîe recorded, with concentrations of 0. I 56 mg/I, 0.3 125 mÿl and 0.626 mgll and above respectively. These results indrcatethat the sensitivity of the larvae to Temephos is excelleÀt. In effect, the CL 95 oi the low mortaliÿ (onlydead larvae) is up to 0.66 mg/I. Two river trials of the Temephos were conducted in 1999 on the Mbaka and the Lufilyo. Forthis latter watercourse, the section chosen was about 15 km long. This stretch was treated at a dose of0'41/m3 i.e. a concentration of 0.33 mg/I. Due to the probleÀ of inaccessibility, no evaluation was carried out before and after treatment beyond the Lufiiyo-Rumakali confluence. As for the results obtained on the Mbaka, they indicate a good carrying capacity of Temephos. In effect, for a floiv of 4.3 m3/s and a dose of 0.1 mÿI, the effective carrying capaciry (100% oiuncoupling; *as 7,060 km. Itmust be noted that the clear nature of the river water (turbidiÿ lower or "quà'i to 5JTU), and itstemperature ( 18- 190C) contributed to lessen the effect of the Temephos. The latter first of all settles onthe .p-articles in suspension (need for a high turbidity rate), which are then injected by the larvae.Besides, any temperature lower than 2l.c becomes u ii*iting factor for toxiciÿ of organophosphorous compounds (particularly Temephos). Between July and September 2000, two sensibility tests were conducted on the Kirvira andLufilyo rivers. with a CL95 of 0.384 mg/l for a high mortaliÿ rate, the results indicate a good sensibiliry to Temephos on these two watercourses. A mortality rate of 100% is observed at 0.625 mg/I,but some moribund_subsist at doses of 0.625 mgand I.25 mg/I. The river tests of the Bt H14 Tecknar on river Mabaka show that at the normal dose of 0.72 mgllby m3/s and a flow of 2.5 m3/s, only 4l .3%o ofdetachment of older larvae at 4.5 km from the point ofspraylng were recorded. The maximal effective carrying capacity-observed is about I km. Besides, onRiver Lufilyo, at a dose of 0.54 I per m3/s, and a flow o1s,sso m'/s, the nlo.tuiiÇ orold Iarvae rs only16.2%. The efficacy of Tecknar was almost zero at 6 km. The first ground treatment campaign meant to eliminate the S. damnosum s.l. of the Tukuy,r:focus through Temephos spraying, tookplace from December 200lto February 2002, The three basinsof the focus (Krwira, Mbaka, Lufilyo) were submitted to weekly treatment with remephos for six weeks,at a dose of l'33 mg/l. Each week, the insectrcide *u. .p.uy.d at 53pornt, and a total of ggl lrters of v- 10 Temephos was used for the entire campaign (fig. 8,9). The results indicate that prior to treatment, 35breeding sites prospected sheltered all the pre-imago stages of the S. damnosum ..i. Aft". the first week of treatment, no breeding site visited on the main rivers was found to be positive (fig. 10, l l, l2). On the contrary, two positive breeding sites were found on the tributaries (on the «asyaÙÀa and a triÉutary ofthe Mbaka (Mb300). The total absence of nymphs indicates, however, the excellent efficacy oith"Temephos. d) Isolation of the focus The data acquired after the works of Walsh and Maegga (1996) indicate that the Songwe River, a natural frontier between Tanzania and Malawi in the downstream section, shelters the S. damnoru... l. (NOTF, 2000). Besides, tributaries of this watercourse take their source from the territory of the focus, mainly along the Mwalisi. The latter is the main tributary of the Kirwrra River. It flows into the section that shelters the S- damnosum s.l. (Barro,200l). In addrtion, a number of tributaries of the Songwe may, from this nver, constitute the contamination corridor of the Mwalisi River. Finally, the Son[we and Kiwira rivers are close to each other, near the border post at Lake Nyasa. It is also worth noting that in the South Eastem part of the focus, some Km from Lumbira, is theKilondi River. It is big, perennial and may also shelter the S. damnosum s.l. Since this river and theSongwe River are located outside the Tukuyu focus, could the latter be isolated? 4.1.4. CDTI status in the Tukuyu focus The CDTI project in the Tukuyu focus within I year. The data collected between May 2000 andApril200l may be summed up as follows: ' The population of the Tukuyu focus is broken down into 46 villages, 38 of which are in the Rungwe distnct, and 8 in that of Kyela. These districts are located in the meso and hyper- endemic onchocercal areas. ' In November 2000,261 boxes of mectizan, representing 130,500 3 mg tablets were supplied to the NOTFs. For activiÿ implementation, 82,635 US dollars (of which 47 dollars was transferred to the NOTF) was put in place by APOC. This funding was used to procure material and to cover expenses relating to fieldwork. 87 to 100% of the training objectives for technrcal personnel involved in the CDTI were attained. The inhabitants around the Tukuyu focus are estimated to be 84,310 persons, 65,2ll of whom were treated with 123,000 ivermectin tablets. The rate of coverage is 66%o. Non-eligible persons (children below 5 years, expectant women, patients), and absentees represent l7o and 9.7%o respectively. This means that the coverage rate of 660 îs excellent, since the number of people who refuse treatment represent only 0.3%. In conclusion, it could be said that CDTI is going on satisfactorily in the Tukuyu focus. The arrangements made (namely undertaking treatment in the dry season, providing financing, and acquiring tvermectin in time) should contribute to improving the therapeutic coverage rate of the next CDTI campaigns. 4.1.5. Budget for vector elimination activities For thc stafl-up and conttnuatton of eltmrnation activrties. AIIOC provrded regular financral asslstance on the basts of letters of agreement (contracts). Thc table belorv suuts up the budget component of the project. I I a11 Period covered Cash transferred to ficld Amount spent US$ Purchase equipment o Total cost Oct 99 25,01 I I1,880 100 35 Oct.99-S 00 50,717 32,518 92,455 124 973 Oct. 00-Scpt 0l 43,199 29,216 8,000 37 216 Oct. 01-Scpt 02 48,983 NA t7 940 t7 940 Total t67,gl0 73,614 206,750 290,364 4.1.6. Discussions - Remarks Given thc various results presented above, it appears that prior to the start-up of the activities ofAPOC, several pieces of technical information were available, due to regula6u*.ÿ. carried out in theTukuyu focus. This data helped to select the focus for vector eliminatiàn activitie;- However, before starting control, APOC assistance helped to cristalise some points. These included mainly: choice ofcapture points, determination of the duration of larvae life on the field, determination of vector characteristics on the entire focus, the sampling and distribution of all blaci< fly species found in thefocus' the determination of insecticide spraying points, the effective carrying "upu"ity of the fe*ephosand the sensibility of larvae to the chemical on the main rivers and tributariei, una nütty tte t ainirg àipersonnel on all aspects (technical, practical) of entomological evaluation. These results are analyzed inthe paragraphs on the distribution of the S. damnosurn s./. in the focus, isolated from the focus, vector control and entomological evaluation. a) Distribution of S. damnosum Vector elimination is the result of total efficacy of larviciding of all vector breedrng sites, which had been recorded over a sufficiently long period. But the spraying points meant to cover the entirebreeding sites went from 26 (Walsh and Maegga, 1996) to sf (earro, z}oz), Thus, follorvingprospection, it appears that the main tributaries of the Kiwira and the Mbaka a.e almost all colonized bÿthe S. donutosum s.l- [n addition, the small streams, which enter the watercourses (main rirers anâtributaries), rvhose stretches shelter the S. damnosum s.1., are also colonized by their embouchures. The resultsof theprospectingcarriedoutin 1998, 1999,2000and2001 indicatedti,attneaistibutionof theS' dantnosurn s./. in the Tukuyu focus is more important and more extensive than the limits mentioned inthe Walsh and Maegga report (1996). The onchocerciasis vector is found both upstream anddownstream of the said limits. Besides, given the great number of secondary tributaries, it is probable that some flow during a part of the year (even all year round), hence the pâssibility of breeding sites sheltering the S. damnosum s.l. (Barro, 2002). This means the current distribution of the S. damnosum in the Tukuyu focus, is perhaps notdefinitely established. However, it is of utmost importance to identiÿ the S. daÂnosum s.l. found on the various watercourses. In effect, Maegga (2001) notes that for the pu.t tt.."l*.., tto larvae harvested have not undergone any cytotaxonomic identification. And yet, some bieeding sites (for instance Mwahsi on the Mbaka) shelter several pre-imago stages, rvhereas the number of bies/man/day remainslow. This contradictory status poses a problem of the identity of species, rvhich are so anthropophilous. Bcstdes, thc identification will have to do with the tnbutaries (namely Rivers Mrvati and Mtumbrviz), River Songwe in Tanzania and in Malawi. For the latter, Maegga (2001) proposes that a joint missiop of Tanzanian and Malawi entomologtsts should prospect the Chipita and Misuka mountains in the northernprovincc of Malawi, which is adjacent to thc Bundah and Umalrla rnountarns of the Tanzanian drst'ct oI lle1e. b) Isolation ol thc focus -l'he hrst condition requrred for unde(aklng vcclor clrmrnatiol rn a focus rs that rt must bc rsolatcd. [n thc case of the l-ukrryu focus, the essentral geographical criterra (presence of naturalbarrrcrs), arrd cytotaxottomic rdcntrfication of tltc vcctor antl rts urlrqucncss to thc focus (S_ 4ttttttt.-st,tt. 88,3 55 T2 Kiwira ÿpe), made some authors (Walsh and Maegga,1996; Le Berre, 1970) conclude that the saidfocus was isolated. On the contrary, other works (Guillet, 1981; NOTFs,2000i Barro,2000 and 2002) reported the presence of the S. damnosum s.l. in the middle course of the Songwe Riu"r, which is a natural frontier between Tanzania and Malawi. Besides, the numerous small tributaries of the Songwe,during the period of flow, could be sources of replenishing of the S. damnosurz s./. Of course all thesé watercourses are found outside the Tukuyu focus, but the flying ability of the S. Damnosum s./. is such that it can get to any breeding site of the focus. It must be noted that iome watercourses are so close tothe focus that simple dispersion would be sufficient. These last results call for another entomological evaluation of the Songwe basin, located on the western side of the focus in Tanzania, but also in Malawi. The same might go for the Kilondo River, located in the southem part of the focus. This river i. Uig,perennial and could shelter the S. damnosum s.l. Meanwhile, there are doubts as to whether the Tukufr-r focus could be called an isolated focus. c) Vector control The sensibility tests conducted in 1999 and 2000 by the OCP team (Bano) underpins the observations made in previous works (Guillet, 1981; Walsh et al, l98l; Garms et àt, t936y, and confirm the very good performances of Temephos with an active matter of 20%o emulsifiable concentrate. Not only did the river tests help to solve the problem of carrying capaciÿ of the Temephos, but it also showed the superiority of its performances, as compared to those of the Bt H14 Tecknar. Thus, the first vector elimination campaign proved to be efficacious, for after only a week of treatment, no positive breeding site was found on the main rivers. Additionally, the total absence of nymphs also shows the efficacy of Temephos on the breeding sites around the tributaries. This chemical rémains the selected insecticide for conkolling the S. damnosum s./. in the Tukuyu focus. For each series of spraying, there is still a problem relating to treatment cycles, accessibility to spraying points, and the dttermination of insecticide quantities to spray (especially in the_absence of a spate gauge). Treatments was weekly, this time lapse between two teatment sessions sufficiently covers the duration of larvae life, which in view of the water temperature (180C-190C), is at least two weeks. d) Entomological evaluation The entomological evaluation is the tool for appraising the results of insecticide treatment on the vector population and parasite transmission. The data collected, though has information that may differ from a document to another, may be characterized by some traits as follows: the captures have great variation in the number of females harvest from one year to another. Thus, for the same capture point, the same month (practically the same conditions), and the same number of days of capture, the MBR recorded in 2000 at Tapio-Bridge is 3 to 607 times higher than that observed in 1999 at the same capture point. The same goes for Kambasegela, Lufilyo crater and Lwangwa-Masako. It is generally agreed that, apart from the periods of re-invasion, when the black fly densiÿ lowers, the physiological age increases, and üce versa. The results obtained àt Tukuyu do not tally with this rule. The dissected black fly population seems, in all periods, to be made up of young females. It must be noted that this part of the population is usually captured in the first hours of the morning (7.00 a.m.-9.00 a.m), or in the last hours of the aftemoon (1600-1800). No infective female was captured in 1999 at Kambasegela, Lufilyo-Crater and Tapio. And yet 527 parous females were dissected, of which 55 were infected. Even at Lwangwa-Masako, only 3 infective females were recorded. Certainly, the MTP is nil for some months of 2000, but each of the ATp obtained at the different capture points is high (minimum ATp=l12 at Lwangwa-Masako; maximum ATP:282 at Tapio Bridge), wtth a tolerable limit (threshold) of 100 Lilmarÿyear in the savanna zone of West Afnca. â , et3 4. 1.7. Conclusions-suggestions Thc "vector elimination project" in Tukuyu now has weak point, which must bc underscored inordcr to make control activities more effective. For the attainment of the s"t ot,,""iire, r,ue would likc tolist sornc elements on which it would be necessary to dwcll. - vector elimination requires total efficacy of larvicidrng, which is undcrtaken on all brccdingsitcs' Given the topography of the terrain in the Tuku-yu focus, it is of absolute necessity tocontinue with prospecting, especially in periods of low water when thc carrying capacity ofTemephos is considerably reduced. - The need for larvae controls to evaluate the efficacy of larviciding, the probable increase in thenumber of watercourses to be treated, and the topography of the tîrrin'r"qure, rvith respect toscrvice quality, thc recruitment of temporary staff durrng Lach control "o*pàig,- The water levcl gauges in the focus now are generally làcated at the extrcm. Jno. (upstream anddownstream) of the watercourses. Due to this, their exploitation is difficult in the middlecourses' which prove to be the areas with the highest black fly densities. Àesides, there is nowater level gauges on the tributaries. This situation needs to t" "o..."i"a t.rouing gauges,updating of tarase graphs), in order to make for good projection of doses and quantisr oflarvicides to be sprayed. - In order to monitor the evolution of the settlement of lotiçal organisms, apart from black flies,under the effect of black fly larviciding, it i. n""".r"ry toÏui".".r"*."Lïyaro-biological data.It is therefore of utmost necessiÿ to collect the maximum of data À'n-.n,on,ofauna andichtyofauna. - some authors affirm that the Tukuyu focus is isolated. others, however, given the proximity ofthe songwe River, its tributaries and the presence of the s. dantrtosurttr.l. In .o*. *u,..courses,have reservations on this. It is thereforsnecessary to rna..tut. u.,..,to*oiogi""r re-evaluationof the basin of the Songwe in Tanzania and Malawi. In addition, and in or-der to conflrm orinfirm the assumption of a re-invasion of the treated zone by the exogenous -5.-clarrtnosuru in thefocus, it is necessary to identiÿ the vectors, with precision. - The results of insecticide treatment on the vector population, and the transmission of the parasiteare appraised, thanks to the entomological evaluation. But the current data on captures shorvsome serious disparities. It is imperative that vigorous action is taken (sensitization, supervision) in order to make these data more reliable. In actual lact, the capture and dissectionresults raise some issues: * were captures carried out according to the standards (7 a.m. - 1800), or only at certain timesof the day (namely in the morning, given the physiological age)? * Is the search forstages of o.volvulus inparàui femJes sufhciently done *,ith precision? - The implementation of the "vector elimination" project at Tukuyu .rppo... matenal means andlogistics. The latter, which are made availabie io the prolett by Apoc, are not parriallyallocated to the said project. A solution will need to be found, so that atL tne logistics madeavailable by APOC will be actually devoted to the implementation of the project. ln view of the various points above, which sum up the various difficulties that camc up during thepractical implementation on the field, the eradication oithe s. danmosurr s.l. b1, ground treatment rn theTukuyu focus, risks to be an objective that is too ambitrous. on the other hand, tlî therapeutic coveragerate (66%o) and that of persons (o-3%) who refuse treatment with ivermectin, indrcate that cDTI is gorngon sattsfactorily in tl-re Tukuyu focus. The measures taken (namely, undertakrng i.àu,-"n, rn thc dryseason, fir-rdrng financing, and procuring ivermectin in trnre) should contnbfte tà rmprovrng thethcrapeutrc co\/erage rate of each of the neit CDTI campaigns. l4 4.2. BIOKO F'OCUS The island of Bioki rs a nlass oIcarth of volcanic origin of 2,017 sq km (72 kn-r long and 35 km widc). I1 is located in the Gulf of Guinca, on the coast of Cameroon and Gabon, Ùctneen lultude, :o+giN and 30l2'N and longitudes 1207'E and 12040'E. The island is characterized by a very rugged relief, made up of mountains, some surnmrts of whrch arc partrcularly high (Basile p.rt, :Ollm; Caldcra daLuba:2661 m; Biao peak: 2009 m). The chmate of equatorial type, with rwo scasons: a dry season (November to March) and a rainy season (Apnl to Octobcr). Thc annual average temperature is 250C. Rainfallvaries from l930 mm in thtNorth to 10.990 mm rn thc South (fig. l3). The island of Bioko belongs to the tropical forest belt. About 90% of the territory is covered byforests- They are particularly dense and entirely cover the rivers, which are very difficult to access. In the upstream and downstream parts of the only main road, only paths link cocoa farms, which provide access to the rivers. The hydrographic network (fig l4) is made up of small low-output rivers, which descend from the mountains. Some watercourses don't have buffer zones (estuaries, iagoon)); They flow directly in the sea, hence the influence of the seawater on their aquatic fauna. Due to the slope, tÉe rivers flow fast(0.3 to I m/s) and the current is turbulent. They are particularly numerous (247),'but short. The average length is about 7 km (maximum: l5 km). Each watercourse shelters several breeding sites. The epidemiology of onchocerciasis recalls that of West African tropical forests (Mas et al,1995). The average prevalence is about 15% (85% in persons aged over l5). For CDTI, the targci population is estimated to be 60,000 persons. Thc Bioko island rs the only tsland knorvn, to date, to be endemic u,ith onchocerciasis. The vector is a member of the S. damnosum complex, identrhed under the name S. vahense, Bioko spe.The geographical location of the island shelters it from re-invasion. This isolation, +O km frorn ihe Cameroonian coasts, led to the thought of vector elimrnation, coupled with ivermectin distribution, which started in 1990. 4.2.1. Nature of rvorks The studies on the onchocerciasis vector on the Broko rsland started in 1989. Then a TDR study on the feasibility of vector elimination in this focus was conducted in 1996. Finally, in 1999, various complementary studies rvere carried out under the pro.;ect, financed by APOC, and entitled ..Vector ehmination of the Bioko Island". The objectives are specific to cach study, and are presented as follows: a) TDR study on feasibrlity determine the productrvrty ol larvae brecdrng sltcs ln the dry season; trace the plans of rnsecticrde lreatntent; cstablrsh thc rdentrty of vectors, tn re latron rvrth that of black flies of the rrearcst zoncs, u,rth a vrel to appraising the extcnt ol- rsolatron of tlicsc vectors; cvaluatc lhc possrbilrty of rc-ruvasron lrour thc coasts; ctlllect all usclrrl ttrlitrtnlttttltr t«r tltc rnrPlcnrcntatr()r) ol'thc "r,ct:tor clrrrrutatrr-rn" pro;ccts. lt) E,lirnirratirrg the vector fronr thc Bioko islln«l lrarn thc natronal tcaur on thc colleclron ol'tlasc cntorrrologrcal clala; coilcct entonroloqtcal basc data, t c ; 15 - establish base data relating to the impact of treatment on the environment (obtain base data onthe aquatic fauna; evaluate the impact of Temephos on the invertebrates and ichtyofauna and rivers of the island); - study the sensibility of larvae population of the S. damnosum s.l. to TcmepS.s; - study the dyramics of rivers and their tributaries; - t undertakc a first ground treatlnent campaign, and cvaluatc its impacl on thc transmissio, ofonctrocerc lasls. 4.2.2. Outcomes obtained Thc vector elimination project is the result of several years (at least l0 years) of preliminarystudies, toward dctcrmining thc feasibility of such u, op"ruiion at Bioko. The varrous results arepresented below, in items entitled: isolation of the island, prospecting, larvrciding and entomological evaluation. a) Prospecting ofbreeding sites The works carried out in April and May 1996 by wilson, indicate that 224 rivers wereprospected, i.e-91ÿo of the entire watercourses of the island. At this period,20 of the rivers prospecteà were inaccessible, 17 of which sheltered the larvae of the S. vahense, Bioko ÿpe. on the contrary, 130(58%) of the rivers showed a flow, and 45 of them (2ro%) were positive riihe pre-i-ago stages ofSimulidae, 23 (10%) of which are of the s-. damnosum s.l. The 2Ô7 prospecting 'sessions carried outenabled a breakdown of the rivers into two categories: those that shelte; the S. daîtnoru,r r.l.,and thosewhose flow was sufficient for the settlement of pre-imago stagcs of S. datrtno.srrrr s./. [t must also benoted that 21 rivers could not be prospected,12 of which rveà capable of sheltering s.dantnosttnt s.l.breeding sites. With respect to cytotaxonomic belonging, the 474 specimens examincd indicated thatthey had exclusively to do with the §. yahense. Since its ikomosome characteristics do not correspondto those oI the standard yahense, it has been baptized the s. yqhsnsc, I]ioko spe . The numerous prospecting activities undertaken rn January-February 1999 (Bano) con{irm thatthe rivers are numerous, short (i k " long in the average), with falls and rapids. Tàeir florv rates weregenerally lorv (lower than 1 mt/s;, hence the insignihcant invasion by the S. datrnosutrt s.l. Even theartihcial supports were not densely colonized in the third week. [n addition, most of the larvae were attntermedtate stages. No pre-imago stage was harvested beyond an altitude of 600 metres or in rvaters whose temperature was lower than22o5C. In March-April 1999, Meyer carried out a series of prospecting of rrvers of the Bioko Island. He concludes that most of the watercourses are protected by a luxuriant vegetatron, hence the difficulry inprospecting. The South, which accounts for about 40% oî the territory, is inaccessrble on the ground. Inthe^dry season, the flow rate of watercourses is generally betrveen 0.2and 1 m3/s. Cool water(190C<T0<260C) and clear water (turbidity generally làu,er than 5JTU), florvs on the rocs ground at an average speed of 0.5m/s (0.3m/s<speed<1m/s). The pre-rmago stages were rare, due to the fluctuationsin water level, following rntermittent rains. Prospectrng on th" Musola and the Eba (tnbutary) indicatethat betwecn 500 m and 800 m, there was no S. damnosutn s.l. Cheke et al. carried out new prospectrng rn Apnl 1999 on I I rrvcrs olthe rsland. The objectrvc was to detcrmine the maximal altitude at whrch thc S. damnosum s.l could colonize thc breeding sites.Prc-irnago stages werc harvestcd on the Trburones rrYers (North), Musola, goofo, Apu, Coo andBaloapr. 'I'he trials conducted at 345 m,554 nr antl 808 m could only cnable the collcction of S.danrtrosut.t.t Srmultdac. It is to bc noted that it u,as thc first tinrc a positrvc brcedinc srtc \\,as disco'erecl on the []ekrlltr ln Dccenlbcr 1999, prospcctrng was on solnc \\'atcrcourses rn the regron of Maluba. -l5e results lrrcscntcd by MCCall (1999) indicatc Lhat24 sttes, rncludrng 8 at altiru<lei:so-r,1gônr) rvcrc vrsited-'l-hc § damnosum s.l. (1lre-imago stages) was encouulcrcd rn fivc rrvcrs (Nalc, Baloapi, -l-oa, Bioco anda rl\/cr wrthout a namc), which do not al)l)car on tlrc lrst drau,n up by \\/rlson f iOlfr; No posrtivc 16 breeding sitc was found beyond an altitude of 600 metres, nor in the waters with temperatures below220bc' on thecontrary, in the Moca region, two biting females were caphlred at 750 and 1,250 m. Atthe timc of the investigation, the flow.ri. *u, 1.05,0.14 and 1.05 m3/s on the Apu, Biala and Malahorcspectivcly. As part of thc studies on the distribution of pre-imago breeding sites on thc island of Bioko,54rivcrs were visited at thc beginning of thc rainy s^eason llunJ-luly). Mas et al. (2000) conclude that outof thcse watercourscs, water tempcrature was 250C. [n addition, out of 52 acceÀsible rivers, g shelteredprc-rmago stagcs of the s- damnosum s.l- It is to be noted that during the samc p..ioà, a Iot of adult Sdamnosum s'l were captured during the prospection. The prospection carried out i., January-February2001 by Meyer et al., just before the beginningof larvicidinj *u. to determine access points to therivers, rivers to be treated, larviciding points und do.., to be ap"ptiea at each ur."Ji"g .ite. 39 sites wereLherclore prospectcd among which 8 were having s.datnnosum at pre-imago stages. fuater temperaturesfluctuated between 1809 and 250c. Flow rates were berween o.r to s*jlr: Tî;:;..;irl,o" *u. sprayedat 40 points, and out of the l0 breeding sites controlled after treatment, 3 were found to be positive. In February 2001, Meyer and 'wilson undertook prospecting of the southern part of the BiokoIsland, between Riaba and Luba. out of 4Orivers, they noàd ôu, *"in basins graav, üoaba, osa, ole).Each of these rivers is a series of falls and rap_ids. At the time of prospecting, the osa River was almostdry, but the other three had good flow. The flow rates were 20-j0m% r;;i-ô;ii o., tr," Moba andole respectively. These flow rates are such that the BT seems to point to the need for treatment ofbreeding sites, except that these treatments, preferably aerial, would take time due to the nature of therelief. Pre-imago stages were harvested in abundance, sometimes, on these watercourses; they usedIeaves and stems that stand out of the water as supports. As for the small tributaries, they were coveredwith vegetation, but due to the topography of the terrain, there are openings that should make aerialtreatment possible. b) Captures-dissection-transmission Right from 1992, the captures made on the Sampaca and Timbabe rivers helped to establishannual fluctuations of the MBR (fig. 15, 16). From January to April, black fly a."tiii., were generallylow (MBR<100). on the contrary, from May through December, the MBR fluctuare between 300 and4,000, and between 1,000 and 8,000 at Timbabe "Àd sr*pu"a respectively. The maximum caprure rsrecorded in October. In 1996, the dissection of 56 females enabled Wilson to observe [4 parous ones (25%) , 2 oîwhich were carriers of infecting larvae. For comparison purposes, 369 females that had been conservedin alcohol since 1993 were softened, coloured and disseàteà. rn" results indicated 42 infected females(11.4%) and 8 infective ones (2.2%) BetweenJanuaryandApril lggg,3146femalesrvereharvestedin2gdaysofcapturecarriedout by the national team at Sampaka, Barley Corn, Musola and Balada Luna ouu. Âmong the g7g femalesdissected, the physiological age fluctuated between 14.8% and 11.3oÂ. The infestation rates rvereparticularly high (infected females: 44oÂ; infecir- e females: g%). In March 2000, Mas and Tirados recorded l4Lillo0o parous females and a MTp equal to 15.Thcse results helped to extrapolate the data of Gcenen (1993), and to obtain a rraxrmum of 400 Lrl,000 Parous and a MTP of l'600. Finally, rn 1997, Mc Call and Mas observed 1,440 Lil1000 parous femalcsin thc dissection rcsulLs. C)apturcs, lbllou'ed by drssccttons, wcrc carrrcd out by the natronal tcanr ln Aprrl-May 2000 o,thc Sarnpaka (Sampaka), Apu (Barley Corn), Musola lMusola) and Ruma (Balacha ol'I{iaba) rivcrs.l'able 9 indrcatcs tltal rn 3l days, 5138 femalcs were captured, 2,890 drssectcd, of which 1,2 l5 rvcrc Parous (42%\,85 infccted (6.9%), and 25 rnfcctive (2%). The avcragc black fly density for thc pc,ocl\\/as about 166 bites/man/day (mrnimum=40, nraxrnrurn:383), hcpce th; usually high MIll{ a T7 (minimum=1305; maximum=11,475). Taking into account a distribution by point of capture, thephysiological age fluctuated between 33.5%o and 53oÂ. With respect to infestition rates, they werebctween l-6Yo and ll.5oÂ, and between 0.5% and 5o for the infected and infective parous lcnrales rcspcctivcly. Transmission was lowest in May at Balacha (MTP=ll), and highest in April at Musola(MTP:270). Thc results of thc captures carried out in February 2001 by thc national team (table I0), duringlarvictding, is as follows: 9 capture points, l7 days of capture 1i to: days per poiàty,3,293lemales captured, of which 1304 dissected. The parous fcmale percentages go from'2i..à% to 64%o, and theinfestation rates are from 5.3% to25%o (infected females), from 0 togo)o(infective females). Apart fromMoca at river Chuba (6 females, MBR = 300), the black fly densities ivere relatively high (minimunrMBII=2970; maxintum:10,380). The trials carried out at thc upstream part olthe watercourses helped to capture 632 females, of which 149,279,198 and 6 were captured at altitude 550 m, 600m, 7g0 m ànd1,250 respectively. In addition to the February results, those of the captures-dissection of the other months of the year 2001 are indispensable for appraising the impact of the first treatment campaign on onchocerciasis tansmission. These elements should be available at the project Coordinato.'s, fo, oi Zô;iNovember 2001' Dr. Mas wrote to the Director of APOC: "J.M. Mba, ento-rnology technician, is sending results of the Simulium catches and dissections, on a periodic basis, to Dr. Wilson". c) Preparations towards the lirst ground larviciding campaign At the end of prospecting conducted on all the watercourses of the Bioko Island, Wilson (1996) concluded that 1,020 km of stretches, belonging to 52 rivers, were to be subjected to larviciding. The "vector elimination at Bioko" started in January 1999. From this date to the end of July2000, the various activities are summed up as follows: In January 1999,a team of external scientists stayed at Bioko. Advantage u,as taken of their stayto train four entomologist-technicians on fieldwork (capture and dissection of Élack flies). Besides thi;,two scientists of the Spanish Cooperation underwent training at OCP, to enable them ensure effecti'e supervision of the collection of entomological data. Two insecticide tests rvere conducted in January-February 1999, and the results shorved thatlarvaeofthe.g. donmosumofBiokowereverysensitivetoTemepÈos. Ineffect,Barro(1999)notesthat with 100% of mortality at 0.3125 mg/I, the results of the insecticide tests conducted on the lanaeharvested in the Musola and Apu Rivers were excellent. These sensibilrry studies indicate that at florv rates of 0.14 m'/s, 1.05 m3/s and 1.6 m3/s, corresponded to the effective carry capacities of 650 m,25 km and 38 km respectively. In March-April 1999, works on the impact of insecticide treatment on the environment rvere carrted out tn thc Bioko focus by scientists from the Museum of Natural History rn London, and from the Water Resources Institute of Accra. These studies were aimed at collecting üase data for an impact evaluation on larviciding of the non-target fauna (namely rnvertebratcs and fishl Meyer (2000) notes that most of the rtvers may be trcated lrom thc bndges that span the main road. Thc latter is locatcd at an altitude of between 100 and 400 m, and 14 km fiom thc sea. The ri'er zonc, wlre re the pre-imago stages of the S. danurosturr arc most numerous, rvould thus, be covcred by treattrlents conductcd from the bndges. I{c also recorunrcnds that aerral prospectrng be undertaken in thc southcm parl of the island in 200 l, in order to collect information on thc acccssrbility of rivers, and theproductrvity of the rr breeding sitcs. At thc erld ol'2000, and alier scveral sclcctrun lests, srx pcrsons \\,erc trarned rn llcldrvor.k: Irarvcst and rdentificatton of larvae, nymphs and adults of the S. dontnostttrt.s.l., harvest oI larvac of thc Sdutnrtosutrt s./. tn thc Carnoy for the cytotaxonomrc studrcs, capture and drssection o1' black flrcs, cleternrtnation of larvac stages of O. volvulus, conservation of parasrtes tor DNA analysis, rarsing ofblack [lrcs ft'onl tlte nynrPh stage, rcadrng of u,atcr lcvcl gauges, usc ol-t5e (]1,S, spraylng olinscctrci6c.IIo$'evcr. Mc-ÿcr (2000) satd tlre lirst p|r<lund trcirtnrcnt rvouki trc prcceclc<l br,'sci,cral rvccks ol r.c- 18 training of technicians on pre-treatment prospecting, experimcntal treatment, insecticidc tests, and hydro-biological activities. Dcspitc thc nunrerous dclays in signatures on documents, and thc late application of ordcrs anddclivery, most of thc matertal and equipment (except a 4 x 4), havc graduaily b".n procurcd and rnstalled at Malabo. Since the first ground treatment was scheduled for 2001, Meycr indicated that all the accessible rtvers bclow an altitude of 500 m be treated every 2 km, and twice a week. All the authors (Wilson, 1996; Bano, 1999; Mas et al, 2000; Meyer, 2000; Cheke, 2000) are unanimous on the fact that the ideal period for treatments is lïom January to April, for the hydrology, rainfall levels and black fly dcnsities arc parltcularly favourablc for a good trcatment exercise. The rnsecticide recommendcd rs Temep6os with an active matter of 20o emulsifiable concentrate, due to its qualities (biodegradable, withoui any toxic effect on mammals and fishes, moderate impact on non-target fauna, and good efficacious carrying capacity). The dose will be 0.3 Um3 of flow rate, hence about 1,200 I will be ,,à..."ry for the "u*puigi(Meyer, 2000). The latter proposes that to lessen costs, insecticide should be negotiaied and taken from OCP stock, which would include the quantiÿ required in its next order. It must be noted that in the event of very low flow rates, (lower that 0.5 m'/s1, it is necessary to increase the dosage, and this requires a greater quantiÿ of insecticide. To address this imperative, a stock of 2,000 I oi Temephos would be a good precautionary measure. Since the Bacillus thuringiensis Hl4 is being proposed ai the stand-by insecticide, in the event of resistance of the larvae to Temophos, Meyer (21000) deems the security stock to be 300 l. Treatment is scheduled to be carried out on the ground, but the inaccessibility of somc breeding sites could enkil the use of a helicopter. From the point of view of expected outcomes, Philippon (2000) notes that the frrst ground treatment operation should, at least, show the feasibility of a control in the norlhem part of the island, and at bcst, its isolation fiom the southern part. The timrng of re-colonization b), adults and larvae rvill have to be carefully monitored. In addition, the analysis of molecular biologl, should allorv lor the detemrtnation of the origin of new black fly populations. On the other hand, this ground treatnlent should not provide a lot of information on a possible aerial treatment. As a matter of fact, it is not obvious that inaccessible breeding sites on the ground could be treated by helicopter, due to the canopy. It seents, therefore, a bit premature to rush into aerial treatment. [t is only after analyzing the results of ground the treatment that a decision could be made. d) Conduct and results of Iirst ground trcatment operation Phrhppon (2000) states that at the end of 2000, base data that are nceded for control rvas available, local expertise was in place, an action plan was drawn up, and the tasks involved in this rvork s,ere entrusted to individuals, who were expenenced in this kind of operations. The first ground treatment operation took place at Btoko during the dry season (January-March) 2001. This was preceded by the collection of pre-freatment data on cytotaxonomy, the sensitiviÿ of the vcctor to insecticides, the drstributron of species (namely at altitude), and the rmpact of larvicidrng on rlon-target fauna. At the ttme of the works only 30 watercourses were flou,rng sufftciently to ntent treatment. As seven (7) of the watercourses have complex basrns (several snrall rnaccessrble tributaries), out ol the 248 proposcd spraying points, only 92 rvere sclectcd. The flow ratcs ol the rivers were lorver than I mr/s, and the water rvas clear (turbidrty<5JTU) and cool ( 190<240C). The personnel in charge of the spraying numbcrcd 10, broken lnto two teams, each of rvhich had a teaur leader, 3 technicians and a driver. lior easc of rnovemcnt, of thc stafl, APOC purchased thrce neu, 'l'tlvota IIrlux cloublc-catrrn vchiclcs lrvo trucks and churns lor lou,rnq vchrclcs In addrtrrtn, thc Spartrsh(.ooltcratton olÏcc put a Landover at tltc drsposal of thc team. In addrtron to the sltrayrng, thrs persor.tncl u'as ttrtegrated tnto othcr actrvrtrcs: capture and disscctron of black flrcs, hydrobrology rvorks, scnsrbilrty tcsts and prospecting o[rivers. Meycr (2000) notes that tlicsc u,orks should conrnbutc to startrng up thc caml)argn, rvhrch would combrnc ground trcatnrcnt u,rth aenal spraying. ! L9 The insecticide for the ground treatment is Temephos, and thc operational dose was 0.4litcrs/m3/s of flow, instead of o.l lÀrls as originally planned. îhis slight i.,crease is due to the prevailing conditions during trcatment: water tcmperature (100C-240C), u"ry lo* flow rates (io*", trrà" r-;i.ll[as[ current (0.3 at lm/s) and fast dispersion of insecticide. The latler was sprayed, thanks to spraycrs (5rn all) Bcrthoud Cosmos l8 type. This sprayer was selected for scveral ."u*n., it is easy to usc, itswcight makes carrying over long distances possible, it allows l-or rapid ,na simpie application ofrnsccticide, the quantity of chemical to bc sprayed could be measurcd with precision, and contact withthc rnsecticide does not corrodc the apparatus. To conduct the entire treatment, a stock made up of 2,000 I of Temephos, 500 I of Bt and 40 I ofRhodamine werc dispatched to Bioko. I{owever, to adàress the problem oi d"loy in stock delrvery, anadditronal I50 I of Tcmephos was sent by air, as matter of urgencÿ. Treatment started on l2 February 2001, and spanned five weeks, at the rate of one treatment perweek' The first two treatment cycles took 4 days to côver all the breeding sites. onlf .iu".s *ho.e flowrates were equal to or lower than 0.01m3/s were not included in the heatment. Tlius, 92 points weretreated each week, with approximately 2l liters of Temephos. of course treatÀni was planned for 12cycles, but it stopped after the frfth application, for technical reasons (mainly i.,r""..ribiliÿ of breeding sites). One of the objectives of the first campaign was to collect a maximum of information, following thespraying with Temephos, in order to appraise its efficacy in the operational conditions of Bioko. Fromthe several data collected, our conclusions are as follows: a) The insecticide carrying capaciÿ was 1 to 3 km, for flow rates going from 0.05m3/s to0.2m3ls- As Meyer indicated (2001), in the event of aerial treatrlred it i, to* carrying capacity will cause an increase in the number of flight hours, and hence an increase inbudget. b) The cycle of pre-imago development was partrcularly long (more than 2 weeks), for thetemperature of water was usually low (190C-240C). The re-colonization of supports after each treatment was, therefore, very slow. c) No pre-imago stage was harvested beyond an altitude of 500 m. On the contrary, adults rvere captured at an altitude of between 500m and 1,250 m.d) Adult population densities fell quickly after the starting treatment. Captures were nil at some points, after only 4 weeks, though no river rvas entirely treated. It should be noted that accessibility to the rvatercourses is very drfficult, and several tributaries cannot be reached. At the end of the first campaign, which was conducted in the northern part of the island, Meyer(2001) and Cheke (2001)' note that due to the inaccessrbrhty of some watercourses, ground treatmentalone may never succeed in eliminating the vector from the Bioko locus. on the other hand, thrs objective may be amved at, in only one season, thanks to an action of ground treatment coupled u,ith aenal spraying. This position was buttressed, follorving the aerial prospecting carried out in the southernpart of the island, and which revealed that most of thc nvers (some of which shelter the S. damnosum s'l') were partially or totally inaccessible on the ground. Thus, Meyer 2001) and cheke (2001) are of the vierv that ae.al operations are feasible for the follorving reasons: t' The stock o[Temephos at Bioko is sufficient for covcring a ground and aerial treatment;ir' An extenston of thc conhact betrveen OCP and the coipanl, in chargc of aenal treatment in Wcst Alrica should be fcasiblc;tir' 'l'he flrght hour, estimated at $1,030, the cost o[the aerial ol]cratror.r. rvould rise to $300- 400,000; tv. .l-[rc protcctcd Populatron rs estrmatcd at 75.000 pcople, rc. About 5 US doltars/,crso,, Irrom thc foregoing, and considertng the cessatlon of OCP activrtres at the cnd of 2002, Meycr and Chckc (2001) are of tlic vrcu' that if thc acrial canrparqn rs not carrrcd out i,2002, ApOC rvrll missthat golclcn opltorluur ty. 20 e) Problems and difficulties encountered at Bioko Various scientists have rcported a number of obstacles to the smooth running of activitics of the "vcctor clirnination project at Bioko". We arc mentioning hcre those that still n"""a to bc addresscd(Mcyer,200l): - The movenrcnt of teams is often difficult, due to pohce and military check points. The securiÿ agcnts don'L seem to have undergone any good sensitization. - Working relations are particularly difficult with the NOTF Coordinator, hence the numerousproblems that might hamper the chances of success of the control effort; - 'fasks are distributed in the national team in such a way that thc absence of an employec(cspccially the NOTF coordinator) may impede thc smooth running of the outht; - The national team may be effective, but it needs discipline and supervision of its activities. These two aspects are, most of the time, lacking. f) Prevalence Mas et al (1995), following an epidemiological survey conducted on the entire island, mention that average prevalence was75%o (85% inpersons of over 15 years). The population at riskwas then estimated to be 62,000 people. Epidemiology is the forest ÿpe, characterizedby 0.g% of blindness, 3lyo of nodule carriers, 29%o of carriers of dermatological lesions, and lympho-adenopathics estimated at42%. Most of the villages are found in the northern part of the island, at )-l km of the sea. Onchocerciasis prevalence is high in all the areas. It is 76.5Yo at Basapu, located at km only from Malabo. As for the highest prevalence (87.1%), it was recorded at Ureca, in the southem parr of the island. An epiderniological survey, conducted in 1989 (Mas et al.) with a population of 1759 inhabitants from l2 r'illages, enabled a prevalence oî74.6% (hyper-endemic) to be recorded. In 199g, after 9 years of ivennectin dishibution to the inhabitants of the same villages, the rate of prevalcnce was only 3-g-2%(hypo-endemic), for a population of 1,167 inhabitants. The same goes fàr the percentages that are carriers of nodules and dermatological lesions, rvhich fell by 2.8o and 7.97o respectively. g) Isolation of the island The vector control activities can only be undertaken ln an isolated focus (Walsh, 1990). That of Broko has a number of criteria for geographical isolation: the closest sources of re-invaston are the neighbourhoods of Mount Cameroon, located in the northeast, and part of the Cameroonian coast in the East. The distances from these paces are 40 kni and 80-130 km respecttvely. The Atlantic Ocean is in the West and South, where thc Principe Island (240 km), Sao Tome and Anabon are found. The latter has never sheltered the S. damnosttm s.l. (Mas, unpublished), and the black flies have not been examined on the other two islands (Santos gracio, 1990). The meteorological conditions severely impede the movement of black flies from the contincnt toward the island. Actually, almost all year round, dominant rvinds, coming from the South or South West, blow across the island toward the continent. Even rn the drrest period of the dry scason, hardly does the rnter-tropical convergencezone (ITCZ) gct to the island (Teran, 1962). I{aving black flies comc from the north or east rs rnrprobable, becausc thrs will be rn the opposrte drrection of the domtnant winds. The cytotaxonomic (Boakye, 1993), cyro-gcnctrcs (wrrson and post, 1994), and Irtorphtllogical crttct'ta (Wrlson, 199(r) rntlrcatc tlrat thc black tll,population ollJrok6 rs cssentrally rnadc up of thc S. vahcnse, Ilroko typc. Arrd yet any possible rc-lnvaslol could orrly cotne fronl thc Calneroontan coasts, rvhcre the .S. Squatnosutn and S dumno"^ttttt s.1. species are found. TI.us mcans tlrat thc Bioko population is gcnetically rsolated. 2t h) Impact of trcatnrcnt on thc cnvironment Brooks and Jackson carried out a survey on the Bioko island in March-April 1999, to determine tlic drstribution of Odonatcs. The results indicate that the l7 sites visitcd are located at altitudes of 1,500nr,600 m and below 500 m. Few odonates (47) at the larvae stage were harvested. This sample(before treatment: 22; after treatment: 25) does not help assess the effect of the Tenrephos on this Sroup.On the contrary, 260 adults representing 24 species, including 6 new ones, were harvested. Distribution is 6 specics encountered solely above 500 m, l7 below 500 m and l3 in both sites. It must be noted that out of the 2l 1 draqonflies recorded on the island, only 7 were found during the sun,ey. A study of the impact of larviciding with Temephos against the S. damnosum s.l. on frshes and shrimps of Bioko, was conducted in the dry season (March-April). Abban (1999) notes that fishes encountered during the survey included 12 families, 21 geneva and 25 species. Ouiof this there were only 9 freshwater fishes whose populations would be exposed to larviciding effects The small-size species made up the majoriÿ of fishes. The shrimps were particularly numerous in all the rivers. Theirbehaviour and reactions were normal. The same goes for the doses of 0.5, 0.25 and 0.125 mÿI. However, a fish, exposed to doses of I and 2 mgll showed disorderly movements, and ended -up becoming stationary in some minutes (2-5). However, the transfer of individuals in a stationary phase in water without insecticide revived them in less than one hour. As for the experiments conducted with high doses, they show that all the fishes exposed to doses of 30 and 15 mg/l ài.d i. less than one hour.At doses of 7.5 mg/l and 3.75 mgll, the time of survival was 12-24 hours and more than 24 hours, respectively. The distribution of the macro-fauna was studied on l0 rivers of the Bioko island (Amase and Amegbe, 1999). The aquatic fauna was regular and generally more abundant belos, an altitude of 500 m. The effect of Tcmephos on the latter, rvas monitored on the Ruma, Musola and Apu rivers located in the east, west and northwest respectlvely of the focus. Out of the three sites, the use of Temephos led to a reductton in the number of chtronomides, but re-colonization is relatively faster. The erthoclamidae were the most affected by the rvave of insecticrde, while the Tanipodinae were less affected i)Training At the end of the vartous missions, it appears that the local staff benefited from theoretical trainrng (background on onchocerciasis), and rvere initiated, on several occasrons, on the use of the technrques applied in the area of vector control: larvae prospecting, capture and dissection of femalcs, estimation of the flow rate of a river (with or u,ithout a gauge), calculation of insecticide doses, using thc flow rate, ground larviciding of black flies, and pre/post treatment monitoring. 4.2.3. CDTI status in the focus Thc population of the Bioko Island is estrnrated at 90,000 inhabitants in 68 communities. CDTI has to do with 61 communrties located in hyper and meso-endemic areas. The target population is about 60,000, half of rvhich lives tn the torvn oI Malabo. Be fore instituting the ApOt i.ogru-*", all thc comnrut]tties \^/ere receiving ivermectrn, based on thc vertrcal approach. But gi'en thc commitntent of the govemment, and the good drsposrtion of the population, the CDTI approu"h .*,u, adoptcd in 2000. Training of the techntcal stafl- tnvolved rn rvennectrn drstnbution was initrated. Sensitizatron \\,as conducted u'rth the populatron to cxplarn thrs neu, rnodc oldrug clrstributron. 'l'hc rcsults ol lhc sccontl ycar of'treaturcllt rn<ircate that out ol 18,22-1 persons, 7.582 rvere trcatcd, r.c. a thcrapcutrc covcrlrqc rate <tf 42o/u. I'hc populatron treatcd is bctr,,,cen thc drstricts of Malabo (2928 persons), Ilanrcy (2270 pcrsons). t-uba (1575), and Rraba (809 persons). For thcse same drstricts, thc gcograplttcal covr'ragc- rs 100%,81oÂ, 100%, and 937o rcspcctively. Abientccism rs high, lor thc trrhabttants are aû-atil tll- llte srclc cflècts <ll' n'crrncctrn. Vcry c[lectrr'.- scnsitrzation shttuld conLrrbtrtc to utcrcasc tlrc varrtlus c()\,cratc ratcs. 22 4.2.4. Budget for vcctor elimination activitics To allow for thc start-up and continuation of vector elimination activitics, thc ApOC progranlme provrded regular financial assistance on the basis of letters of agreement (Contracts). The table belorv surrs up the budget component of tlie project. Period covcred Cash transferred To field in $US Amount expenscs in SUS 0 Purchasc equipmcnt C Total cost March 99-Fcb 00 21,984 I 6,61 8 168,490 185 r08 March 00-Feb. 01 54,776 25,436 124,660 150 096 March 0l-Feb 02 55,390 NA 136,400 136,400 Total 132,150 42,054 429,550 471,604 4.2.5. Discussions - Remarks a) Distribution of S. damnosum s.l. The southern part of the Bioko Island, about 40% of the total area, is inaccessible. On the contrary, several prospecting activities have been carried out on the accessiblc part. These prospecting activities were carried out the whole year, but they were mainly concentrated in the dry season (mainly in January to April), the ideal pcriod for treating larvae breeding sites (Wilson, 1996; Barro, 1999; Meyer, 1999; Meyer eL al; 2001). Despite the great number of rvorks, the results of all the authors aqree on several points: The ,S. darnnosum complex is represented on the Bioko island exclusively by the S. yahense, Bioko ÿpe; Rivers are numerous and short (averaging 7 Km long); Watercourses, protected by luxuriant vegetation, are hardly accessrble; In the dry season, the flow rate of rivers are generally below lmr/s. Water is clear (turbidiry<5 JTU) and cool ( I 9oC<temperature< 260 C); The pre-in,ago breeding sites below an altitude of 500 m, are generally positive, when the tcmperature of the water is higher than 2205C. No pre-imago stages have been harvested beyond 500 m. On the other hand, adults have been captured at altitudes of betrveen 550 and 1,250 m. It is agreed that vector elimination in a grven focus is only possible if all the breeding sites are subject to larviciding. However, thc results of the various prospecting carried out at Bioko indrcate clearly that the rivers arc very numerous and protected by dense vegetation. This means that a number of breedrng sites remarn unknou,n, due to the inaccessibility of u,atercourses. This situation also poses the problem of choicc of spraying points. It must ensure a-100o coveragc of all the breeding sites. Of course , the authors agree that malonty of the positive breedrng sites are located beloq, an altitude of 500 m. I{owever, the presence of adults between 550 and 1,250 m risks undcrmining the chances of success (possiblc re-invasion), sincc the area located bcyond an altitude of 500 m is excluded from larviciding. Besidcs, following the prospectrng undertaken in the southern part of the Island, Meyer (2001) notes that apart from the Musola Iliver, and rts tnbutary, the Eba, no rivcr rvas acccssible beyond an altituclc ol-500lll ltvert ltclorv 50() In, scvtral \\'atcrcourscs tt,cre llartralll,or contplctcll,rnacccssrble T[is 1rcals that no nvcr could bc trca(ccl on tts entlre coursc. :I 23 b) Isolation of the Bioko focus The authors are unanimous in agrecing that the Bioko focus is isolated. In actual fact, it is anisland whcrc meteorological conditions (especially wind movement; Tcran, 1962; Nasti, 1942) hamperthe rc-invasion of the focus. Besides, cytotaxonomic (Boa§e, 1993), morpholâgilut lwitron, 1996)and cyto-gcnctic (Wilson and Post, 1994) evidence make one recognize thàt tn"-S. yahense found atBioko is differcnt from thc standard ÿpe. There is therefore, a geietic i.otrtion,î.'"o*pu."d to the nearcst black fly species, and those found on the cameroonian coasts. c) Vector control Rtvcr tcsts rcvcalcd that the selected insecticide for the treatments in field conditions at Bioko, was Temephos with active matter of 20% emulsifiable concentrate. The experiencJgainea during thepreliminary works, indicate that the vector elimination project at Bioko wàuld i,c.ease its chances ofsuccess, if control operations started in the dry season, and spread over 34 months. At the usual operational doses, the spraying of insecticide is followed by a reàuction in the number of chironomidae,but the re-colonization is relatively fast. On the other hand, fish and shrimp popufurion, are not affected(no mortality; normal behaviour) by the insecticide treatment. This means tËat a t àuon"rrt campaign against pre-imago stages of the S. damnosum s.l. through Temephos spraying in the watercourses of theIsland of Bioko should not have irreversible negative con."quln"., on-the non-target fauna. (Abban,1999), notes that there is a very large gap between the operational doses and the tox"ic doses for fishes and shrimps- However, since the first campaign came off in 2001, it is necessat;;* to undertake apost-treatment collection, in order to assess the impact of five treatment cycles o., ih" aquatic fauna andthe environment. Besides, since some positive breeding sites of the Grande Ruma and Musola Rivers are inaccessible on the ground, their treatment could be subject to aerial treatment. Given the OCp experience, Meyer (2001) and Cheke (2001) recommend the helicopter as the best means for giving theindispensable support to the total coverage of all the breeding sites. This option seems buttressed by thefact that in the south of the island, several watercourses shelter the S. damnosum s.l. which were totally or partially inaccessible. As Seketili (200I) indicates, the fact remains that the use of the helicopter supposes, first of all, responding to a number of questions: - has ivermectin been distributed over the past l2 years? - What is the cost of aerial an operation? 300400,000 US dollars, as recommended by Meyer(2001)? It must be noted that parking rights, and transfer costs of the aircraft are not taken into account in the amounts mentioned above. The same goes for the cost of entomological evaluation, and the cost of tickets, per diem, insurance, etc.. of extemal persons (experts and scientists), who will be involved in the operations; - How many persons will be protected by this operation? For information purposes, the targetpopulation of the island is about 60,000, half of who live in Malabo. There is need to recall that the JAF6 had recommended that the decision to carry out aerial treatments rvould only be after a close analysis of the results of the first ground treatment. d) Entomological evaluation The PAT and ATP are good indicators of the entomological situation, for they quantify the blackfly aggression and the transmtssion of the O volvulus respectivày. On the island of Éiàto, and from the captures made in 1992, Wilson (1996) notes, that apart from the dry season (from January to April), theblack fly dcnsities are high. Thc period from Septembcr to November remains that when the black flics arc most abundant- However, Anonymous (2000) and Cheke (2001) record MBRs between I305 and11,475 in April-May, and bctwcen 2970 and 10,380 in February. This means that evcn in the dry scason, the black lly dcnsr(ics nray be hrqlr. Givcn that thc black fly speclcs involvcd rs the S. claltltrosut.t-t s.l;, it rs probable that thc ralny season rs whcr.r aggressrvencss rvrll be nraximal. Irrom 1996, it has bccn cstablishcd that the fenrales of the S damnosum s.l. captured on the rsland o[Broko had high tnlcstatron ratcs (wilson, 1996). [n effect, the percentage of infectivc females(tlrose susccptiblc lo transnlt thc Parasitc at tlre ncxt brte) was 14.60Â. O.ly th"e numbcr of drssectedIi'rllalcs (56) at thc timc, was arl rrnpcdirncnt to an cnhanced intcrprctation of the results. Thc latter arc, 24 nevertheless, confirmed in 1999 by the dissection of 878 females, which reveal Myo of infected females and 80 of infective females (Anonymous, 1999). Of course the ATP could not be established for 2000,but the MTPs obtained in April and May at the various points of capture arc by far higher (MTp minimum = 130 at Balacha; maximum = 473 at Musola) at the tolerable threshold of tOO LilÀan/yàar in thc savanna zone olWest Africa. The works of Cheke (2001) corroborate the previous results, because apart from the points of capture located at altitude (0<MTP<72), all the othcr MTps are higher than 100(minimum = 3 l9 at Sampaka; maximum =- 127 5 at Musola). The various works of authors agree on this, and indicate that the transmission rate is high on thc Bioko island. The infestation rates recorded recall those recorded on the small rivers of forest areas in West Africa, where the vector is also the S. yahense. From our reference to the results recorded in 1989 and 1998 (Mas et al), it clearly appears that alter 9 years of lreatment with ivermectin, prevalence had gone from hyper-endemic ea.6%j to hypo- endemic (38.6%). Such a change usually tells on the level of black fly infestatron. This assumpti;; is corroborated by the results of some authors. Thus, from Geenen (1993) to Mas and Tirados 1ZOôO1, ttre number of infecting larvae for 1,000 parous goes down from 400 to 74, and the MTp from 1600 to 15. On the other hand, this is not the case, if we refer to the infestation rates recorded by Cheke (2001). The absence of pre-imago stages should mean the exclusion of breeding sites located beyond an altitude of 500 m, from all treatment campaigns. But the adults wee captured between 550m and 1,250 m. The eggJaying points of these altitude females remain to be determined for setting the limits of the area to undergo larviciding. [n effect, these females may come back to lay eggs in the breeding sites located below the 500 m altitude, as prospecting may not have been precise (abundance of brJeding sites, difficult access to rivers, due to vegetation) for detecting the positive breeding sites located beyo.,à the altitude of 500 m. 4.2.6. Conclusions - Suggestions Apart from the feasibiliÿ srudy conducted in 1996, several surveys rvere carried out on the Bioko island between 1996 and 2001. The objective rvas to collect indispensabie data for conducting treatment campaigns and their evaluation. The first campaign of ground treatment took place in February-March 200 1, and the various outcomes, in relation to the set objective for vector elimination, enable the following points to be established: The geographical situation, meteorological conditions and the cyto-taxonomic, morphologic and cÿo-genetic criteria conf,rrm that the island of Bioko is an isolated focus. Given the distnbution of rivers and the prospected breeding sites, it appears that to each prospecting corresponds at least a new breeding site (discovered on a river that is already fisted or not). Besides, the presence of adults at altitude, places the treated zone under the menace of re-invasion. This situation poses the problem of total coverage of breedrng sites by insecticide treatment, rvhich is an indispensable condition for vector elimination. [t therefore, seems preferable to plan the treatment of all the rivers that have sufficient flow to favour the settlement of pre-imago stages of the,S. damnoswn s./. In view of this, punctual investigations should be undertaken to make up for the lapses or the lack of information on the mapping of the breeding sites, the spraying points and the accessibility of breeding sites. The geographical configuration (namely vegetation cover), is such that, apart from a fcrv exceptions, larviciding wrll have to be carried out by ground spraying. Portablc spraying machines (Berhoud ÿpc) would be the most efficacious, for they spray out the mcasurcd quantities of insecticide. 'the ideal period for larvrcidrng u,ould be the beginning of the dry season, whcreas the florv rs still sufficient for a good carrying capacity of the insecticide. The "brccdrng sitc by brecdrng site" treatmcnt could, thus, bc avoided, and thrs u,ill bnng about a nrultrplrcatron ol' sprayrng pornts. l'lie black fly dcnsity on thc Bioko Island rs usually abundant, and transmission rs cxclusively ensurcd by thc S. yalrcnse, Bioko type. The vector characteristrcs (infcstation ratcs, parasitrc loads) rccorded arc hrgh and recall those observed in the forest arcas of Afnca, rvhere the S. yultensa ts also thc r.narn vcctor. t a a 25 The base data and those of impact studies on the environment of the Bioko Island, in relation with the treatment with Temephos, will be indispensable during the evaluation of the control activitics. The collection works must thereforc be continucd. Thus, flor a better knowledge ofl.he non-targct entomic fauna, Yameogo (2001) notes that it would bc desirable to havequalitative sampling of the vegetation (leaves, immerged dead wood), and the under-gravel.Besides, thc high predominance (75%) of the Elmidae on the Lada river, necessitatesinvcstigations on this family and its living environment. On the other hand, the option of organism indicators (namely Odonates), for monitoring thc impact of treatment on the non-target fauna, needs to be reviewed. The same goes for the seleciion of perennial watercourses, which would not be treated to constitute refuge zones. The latter would shelter, not only non- target fauna, but also the vector. Thc local staff, called in to undertake implementation and monitolpg of vector eliminatio' activities' was identified and selected. Staff members had punctual trarlning during the ua.iousinvestigations that were carried out on the island of Bioko. Regular "îutuutiin itechnicalknowledge, professional conscience), followed by re-training, if necessary, is desirable for this staff in order ensures continuiÿ and efficiency of control activities. For example, the results ofApril and May 2000 indicate that the computation of infestation rates (% oi infected parous females, % of infective parous females) and indices of transmission (MÈR, ABÀt;;; still not very well assimilated. It is clear from the various investigations mentioned in the reports that the activities of the local team stop, sometimes immediately it is alone in organizing fieldwork. It u,ould be desirable thatpersonnel be sensitized so that the relational issues involving individuals and/or instiiutlons ao not hamper the smooth running of control activities. To ensure monitoring of routine activities of the national team, it would be proper that the coordinator of the project solicit a progress report, on a regular basis, and be morè pàsent on thefield. 26 4.3. ITWARA FOCUS Uganda is one of the first countries, where onchocerciasis vector control was successful. Thus, thc.S. r/arrurosurn s.l. was eliminated from the Victoria Nile focus, and thc S. rreo,ei temporary kicked out o1'tlre Budongo locus (Prentice, 1974). In the 70s, the use of DDT with active matter of 25%o of emulsifiable concentrate, helped tointemrpttransmissionofonchocerciasisinthefocusof Itwara(Garmsetal., 1994). Duetotheabsence of funding, and the insccurity, control efforts stopped from 1975 to 1971. But in 1990, nerv fundingprovidcd by the German Cooperation (GTZ), and the Ministry of Ilcalth of Uganda, enable datf collcction to continue (Garms et al., 1992). It is under this that all the rivers susceptibte to shelter the S. neavei.s..§. were prospected and the adult population monitored, thanks to the captures, dissections and determination of infestation rates (Garms et al. 1994). The spraying of Temephoi, which as carried out from August 1995, were found to be efficacious, and the results promising, aftLr only 3 treatment cycles. In effect, between 1994 and 1995, the black fly densities went down from 481 to 0 àn the Kijura biidge, and from 365 to 2 at Busasa. Given these results, teatment was extended to the main breedi.,g .it".ii the focus that shelter the S. neavei. The elimination of the vector from the Itrvara focus became an attainable objective. To safeguard its gains, and to contribute to the elimination of the disease, the Technical Consultative Committee (TCC) approved the surveillance and continuation of larviciding of the breeding sites of the focus of ltwara, and all the foci of Siisa and Aswa. This choice is part of-the objectives of APOC, which in some particular cases, is onchocerciasis control, through vector elimination. From 1996, the focus of Itwara was selected, because pre-treatment data was available, and qualified staff and control activities were already ongoing. 4.3.1. Prcscntation of locus The Itwara focus is located around the forest reserve bearing the same name, at about 25 Km in the nofth of Fort Portal (fig. 17). The reserve covers about 20 sq Km, 22o of u,hich are made up of trce vegetation (Howard, 1991). It is bordered by large plantations of tea, subsistence crops and ranchcs along the rivers (Sogohi, Kahamba, Muzizi, Mpanga). This is to say that the original forest has been extensively cleared for the sake of plantations. The rvatercourses are, nevertheless protected by dense forest galleries. The landscape is characterized by rvooded valleys and mountains with altrtudes varying betrveen 1,250 and 1,460 m. Tempcratures are, therefore, moderate. The climate of the area is characterizedby a humid heat, and all-year-round rains. Maximum rainfall figures (1,000-1,400) are observed from September to November. The dn,season stretches from Deccmber to February, but it is never totally dry. Hydrological condrtions are generally favourable, all year round, for the development of pre- inrago stages of thc S. neavei. The larvae breeding sites are found essentially on the §ogohi and its trtbutaries (Wamisc, Nyakrbuguta, Kanaba, Kafunda), the Srisa and rts tributaries (Kyasa, Mohabura) and finally the Asrva River. The area rs densely populated, and onchocerciasis is highly endcmic hcre. [n 1997, 80% of thc 45 lrcrsrlns u'ho livcd in the ncighbourhood o[ the forcst rcscrr/c. \\rerc iufcsrc-d by tftc O t,olt,ulu.s((iar nrs. 1 997). 'fhe black fly spccrcs to cltnrtnatc from the locus rs thc S. neavci s.s., the nrain onchoccrcrasis vcctor (Barnley and Prenttce, 1958; Prentrce, 1974; Ganns et al., 1992). It flyrne capacity is about 6-10 Krll. Thc lrlespan of thc larva is 3-4 wecks, due to the rvatertempcrature, u,hrch bctrvcen l8oC an6 19"C. I 27 4.3.2. Nature o[ Works 'l'he works carried out frorn 1970 to 1997 (cspecially in 1994) in the ltwara focus , dweltcsscntially on - Dynamics of pre-imago and imago populations; - Determination of the duration of pre-imago development; - Vectoridentification; - Distribution of breeding sites with the S. neavei in and around the focus. - Vector characteristics of the S. neavei; - River tests of the Temephos (determination of doses and carrying capaciÿ). - Training of pcrsonnel. As part of the works carried out, with the support of APOC, the national team, in charge of the vector elimination activities, undertook intense activities of surveillance and supervision, in-order to ensure that vector collection is properly done. The activities are summed up as foliows: - Regular prospecting of the main contol points in the main ltwara focus, and in the sub- foçi of Aswa and Siisa; - The capture of black flies at pre-selected points; - The treatment of rivers at intervals of 4 weelcs, in the sub-foci of Siisa and Aswa. 4.3.3. Rcsults obtained a) Prospecting breeding sites The entomological data collected between 1991 and 1994, prior to instituting treatme,t rvitlr Temephos, tndicatc that 38.9% of the crabs captured on the Sogohi river (Itu,ara folus) carried pre- imago stages of the S. neavei. Though treatment rvas discontinued on the rivers on the western side of the ltwara focus, Garms(1997), it must be noted that the latter were not re-invaded. Since the last crabs were found to bepositive at Nyakibuguta in August 1995, the river was treated in December 1995. Nevertheless, the 479 crabs harvested at Nyakibuguta in 1996-1997 were all negative. Besides, none of the l6g3 crabs fromltwara' Srisa and Aswa carried pre-imago stages of the S. neat,ei. The last crab sheltering only one larva of the S. neavei dates back to November I 996, and was harvested on river Sogohi .. The prospecting carried out in May, June and October 1997 in the Itwara focus made it possible to catch 871 crabs, none of which carried pre-imago stages (Lakwo et al. 1998). The same goes for the 50 crabs harvested at Sogohi in February 1998. The Srrsa and Muhabura rivers were also prospected in May, June and October 1997. Out of 614 crabs examined, only 2 carried larvae of the.S. neattei. From N4arch to June 1997, thc sub-focus of Aswa u,as treated with l7.5 I of Temephos. Laku,o et al. (1998) cstabhsh that the post-treatment control conductcd in May, June, August and October enable the sampling oi585 crabs, l5 (2.6%) of rvhich wcre carrying pre-imago sta_ccs Jf tn. S. neayei. In Ivlarch 1997, (Garms), about 900 crabs fronr the Itwara focus u,cre eramined, and all rvcrc ttt'q:lllvc (lttl trllcctrttrr b1'thc S. ncavct). 'l-hc sanrc ucnl for 494 crabs harr'.,srcd r' thc sub-lbcus tll- srrsa. ()n thc- contrary, rn thc sub-lbcus o1'Asrva, tl.rc crabs u,erc infcstcd. In Oclobcr 1991,354 crabs wcrc harvestcd by thc national team in the sub-focus of Srisa (179) and Asrva (175). and 2 (l%) and 4 (2"Â) rcspectrvely, carrred larvae of the S. tteat,ci. 28 From September 1998 to September 1999,7 rivers were prospected in the ltwara focus by thenational team- The 872 crabs captured were all negative. During the same period, only 0.3% of thell84l crabsharvestcdinthesub-focusof Siisacarricdpre-imagostagesof the.s. rteavei. ontheotherlrand, in tlte sub-focus of Aswa,6.l% of the l6l6 crabs examincà were carricrs of the S. neavei. In 2000' the 6 prospecting sessions carried out in the focus of Itwara by the national team helpedto harvesL 5Sg crabs; all were dcvoid of pre-imago stages of the.S. neavei. During t6e same period, 1479crabs harvcsted at Siisa were equally all negative. on the other hand, ne ç7;1"1oi,i,.3674 crabssampled at Aswa were infested with the S. neavei. The infestation rates varied from I .2,yo to l9oÂ. Itmust be noted that before larviciding, 80.4% of the 92 crabs caught on thc Musabira River were positive, whcreas just after 4 treatment rounds, none of the 470 crabs exÀined carned pr"-lnlrgo stages oI the .s.ttctt't,ci. Between January an August 2001, the prospecting of the national team made it possible toharvest 4656 crabs in the Itwara focus (948),630 in-the.ù-fo"u. of Siisa, and 307g in that of Aswa.No pre-imago stage was found on the crabs of Itwara, and only one larva of ihe S. rteaveiwas taken froma crab (0.2% of the population) from Siisa. The highest raté ç0.+u"1of positive "."Ù. *", observed atAswa. b) Captures-Dissection-Transmission The adult capture sessions were less than larvae prospecting. Nevertheless, the following couldbe noted: In 1994, prior to starting larviciding, the dissection of 2889 parous females revealed 622 infected females (24%) and 120 infective ones (4%). Larviciding camed out from June to August 1995 brought about a drop in the blackfly density (table ll). It wenr lrom4gg2 in lgg4 to 3g04 in lgg5, and to 6 in 1gg6, at the capture point of Busasa. The same data gave 6403,2546 and 0 at Kijura and 2390,64 and 0 at Sogohi. ln March 1997 , it was estabhshed that the drstribution of ivermectin only intemrpted transmission partially. In effect, out of 153 parous females examined in t99t, 27.89% were infectedand2.60 rvere infective. In 1992,1993 and 1994, the same data were 684ll3|yol5.6oÂ, 399012G.8%13.5o and 3ol7lzl.g%/3.1% respecti'ely. The number of infecting lanae by 1000 parous females rvas 124 in 1991, 2j6in 1992,169 in 1993 and 176 in 1994. The data collected at Kicheche show that afrer 6 years of distribution of ivermectin, transmission was still intense. ln effect, out ofll5 parous females, 48 (42%) rvere infected, ll (9.5%) rvere infective, and the number of Lil1,000 parous ones u,as 470. The captures made in the Siisa focus in May, June and october 1997, were all negative. Besides, as of February 1998, no adult of the ^!. neavei had been capturedfor two years in the Itwara focus. The same goes for the sub-focus of Aswa, where the captures were nil from september 1998 to september 1999, at the capture points callcd Andrew and Tourist. Lastly, thc cntire 2000 was marked by the capture of negative catches of the S. neovei, at the drfferent capture points of thc Itwara focus, and the sub foci of Siisa and Aswa. On the other hand, 140 S' dttmnosunr .ç./. rvcre captured in the focus of Itrvara (39 females) and I I I females in the sub-focus olAswa. 'flrc dissection o[thesc females drd not reveal any infectron due to tbe O. volvttltts. c) Larvicitling Thc first cxpcrttnents werc carrtdd out by Garnrs rn August 1994 on the Sogohi rivcr, lor assessrrlg the cfficacy of thc Ternephos, and the Bt I'll4 rn the control of thc S. neaver (fig lg). Thet'csultshoq'cdthatat adose of0.l mg/l,Temephosdocsnotelrrninateall thelarvaeofthcs.neavci ovcr l<lrlg clrstanccs. Orl thc othcr hand, conccntratlons ol0 2 and 0.4 mg/t gave bctter results, rvhilc havrng t a 29 no negative effects on crabs. The experiments with the Bt did not give any good results, due to the low carry capaciÿ of this insecticide. In the ltwara focus, the last treatment with Temephos dates back to February 1997. It rvas carricd out on the Sogohi River. But treatment on thc other rivers of tlie focus rvere suspended much earlicr. Thus, the last treatment on thc Nyakibuguta dates back to Decembcr 1995. For the entire larviciding carried out in the ltwara focus, and its sub-loci of Siisa and Aswa, 160 liters offemephos were used from 1994 to 1997. Since this date, punctual treatments have been undertaken in the sub-foci (Aswa, especially). Thus in 2000, 58.75 liters of Temephos were used in the sub-focus of Aswa. The latter was also treated between September 1998 and December 1999. The monthly spraying was carried out at Andrew's pt, Guaging pt, Tourist pt and Tonrs's pt. It nrust be notcd that for logistics reasons (lack of insecticide), treatment in the sub-tocus of Asrva only started in 1997. d) Isolation of Focus The Itwara focus is not totally isolated from the two sub-foci, located around the Siisa and Aswa rivers (Garms, 1997). On the other hand, the entire set (focus and sub-foci) is at least 100 Km from the nearest breeding site (Kashogi-Kitomi focus). Besides, the latter shelter mainly the S. neavei, whose flying capacity is reduced (6-10 Km, maximum) e) Impact of treatment on environment It has been proved that Temephos, at operational doses, is without toxic effect on mammals and fishes. However, its impact on on-target fauna is moderate. At the end of observation carried out in Uganda, Garms (1991) establishes that crabs of the foci and sub-foci of Itwara, Siisa and Asrva, u,ere not affected by the operational doses of Temephos. I{owever, special studies on the impact of treatment on the environment were not conducted in thc vector el imination zone. f) Training Staff rraining was carried out dunng the several works carried out between 1970 and 1997(Garms, l99l). In 1998, the needed staff for the running of APOC activities u,as ayailable, qualrfied and experienced. 4.3.4. CDTI status in Focus The ltwara focus is located in the district of Kabarolc. tn the latter, covered by phase 2 ol the CDTI in Uganda, the total population of the endemic zone is 82,597. This populatron is distributed over 147 communrties, 120 of which are in a hyper-endemic zone, and2l in a meso-endemic zone. In 2000, the rate of therapeutic coverage was'tZo (58,121180,191), and in 2001, it was 73o (60,235/g2,597). Of course the target population of the district is known, but rt is also indispensable to determine that of the focus. This precision would enable a monrtoring of the evolution of the therapeutic coverage rn the focus, and to assess the impact of ivermectin there on onchoccrciasis transnusslon. 4.3.5. Budgct for vector clirnination activities 'l'o enablc vcctor elrmtnatton acttvtttes to contrnuc, tlic AI'OC l)rogranrnte ensurcd a rcgular financral asststance on thc basis of lettcrs o[agrcement (Contracts). The table belorv sums up thc budgct compor)cnt ol thc projcct: t 30 Covered Period Cash hansferred to field US$ Amount spent in US$ Purchase equipmcnt o Total cost Feb.99-Aug00 1 6,1 57 l s,9l7 12,029 27 946 00 I 10,951 NA 12,2gg I Total 27,108 15,917 24,327 40,244 4.3.6. Discussions-Remarks 'l-he rcsults of thc various prospecting works agree and indicate that rvhate'er the focus (Itrvara) or sub-focus (Siisa and Aswa), the treatment of the breeding sites with Temephos brings about a drastic reduction in the numbers of the pre-imago populations of the S. neavei. Even wîen treatment isdiscontinued, a drop in densities is recorded. The post-treatment controls indicate, however, an almost total absence of positive crabs, since 1997 , in the ltwara focus. The same goes for the sub-focus of Siisa since 2000. This means that the entire breeding sites of Iturara and Siisa àre under larviciding. On the other hand, the presence of positive crabs in the rivers of the sub-focus of Aswa, reveals the plesence of non-treated breeding sites. The latter must be listed and included for treatment, for only tot l "o,r"rug.of all the positive breeding sites would make it possible to envisage vector elimination. This objective is achievable, because it is enhanced by the fact that the area to be cleared (Itwara focus, Siisa and Aswa sub-foci) is isolated from the other onchocerciasis foci. In effect, the nearest foci are found at 100 Km and shelter essentially the S. neavei, whose flying capacity does not exceed l0 Km(Garms, 1997). Besides, the authors are unanimous that Temephos, given its qualities (efficacy, good carrying capaciry, moderate effects on non-target fauna), is the sclected larvicide for ground treatment ol the breeding sites oIthe ltwara focus and its sub-foci. The first factor that conditions the existence of the imago population is the pr-imago population. Sincc the latter is very sensitive to larviciding (Anonymous, 1985), this brings abôut a reduttiàn (even disappearance) of the adult population. The results obtained at Itwara, Siisa and Asrva are in lrnc with this rule. Lr effect, since treatmcnt started in 1995, black fly densities (5. neavei) dropped to zero in 1996 at Krjura and Sogohi. As treatment took place, the trend heightened, since no biting female rvas captured in 2000 on the entire focus (Itwara, Siisa, Asrva). The results recorded in 2001 confirm the absence of biting females in the area. It must be noted here that prior to larviciding, the black fly density reached I 9,000 bites/manL/year. From the viewpoint of transmission, the dissectron of females captured before larviciding reveals high infestation rates in the .§. neavei (% infested females : 24"/.; %o infective females : 4%t Besides, after 6 years of ivcrmectin distribution, transmissron was always intense at Kicheche (r of tnfectedfemales:47oÂ;o%ofinfectivefemales:9.5%;470Lill,000parousones). Thesedataconfirm the hyper-cndemic nature of the Itwara focus, and of its sub-foci (Siisa and Asrva). They also corroborate the observations of other authors, who assert that ivermectin does not totally intemrpt transmission. 4.3.7. Co nclusions-Suggcstions -fhe rcsults above indical"e that the treatment of the ltrvara locus and t]re sob-foci of Srrsa and Asu'a hclll to clrminate thc vcctor in this rcgton <lf Ugan<ja. It is therelore rmpcratiye to cont,tue qround tlcatlllcllt, csllccrall;' rrt thc sult-lilcus ol Asu,a, uhicli reniarns actrvc (punctual l)osltrvc brcc'drng srtcs).In cflect rts proxrrnrty ts such that black fltes can casily reach thc ltwara and Siisa brccding sitcs. 'lhe lattcr will have to continuc to bc surveycd with prccisron, during the penods considered to be of high black fly productrvtty, tn ordcr to confirnr that black flres are effectively and definrtely absent from the sard focr t 31 Of course bibliographical data indicate that the S. neavei has difficulty in reconstituting itspopulations when they have been greatly reduced. But the fact still remains that any interruptiJn intreatment contributes to a rapid reconstitution of thc black fly population. [t must bc noted t6at thcfailurcs of trcatmcnt may also lead to the same results (rnôrcase on black fly densities). Rcgular supcrvision by {-rcld tcams (captors especially) should enable fluctuation in density that reflects thecfficacy of larviciding to be recorded. Any treatment failure could, thcn, be qulctty detected andaddresscd, since it would be related to a specific cause. The vector to be eliminated in the Itwara focus, and its sub-foci (Siisa and Aswa) is the S.neavei- This species is however, vulnerable, for under the pressure of insecticide treatment, thepopulation decreases very fast. However, a sudden re-infestation is irnprobable because the .S. rteaveipopulattons rcconstitute very slowly (long pre-imago development; phoretrc aspects), and thedcforestation does not favour the displacement of black flies. In addition, since the fo"rr'i. i.olut.à, vector elimination has multiple chances of success in the area. However, the problem of insecurity needlto be addressed, since in certain periods, this impedes or even stops activities. ln view of the current situation, vector elimination activities in the ltwara focus and its sub-foci(Siisa, Aswa) should be successful. It is probable that the children population does not practically haveany microfilaria carriers. However, the distibution of ivermectin must continue, to take into consideration the longeviÿ of adult worïns of the O. volvulus, which might be carried by otae. patients. I 32 4.4. FOCUS OF MPAMBA-NKUSI In Dccembcr 1996, thc project Mpamba-Nkusi was approved as part of the..vectorelimination project in thc ltwara focus". On the recommendation of the Technical èonsultative Committee of theAPOC programme, the said project was re-defined and separated flrom the Itu,ara locus in 199g. TheProjcct was then approved as a feasibility study of the vector elimination project of the Mpamba-Nkusi focus. 4.4.1. I'rcsentation of focus The area concerned by the vector elimination is located in the northem part of the Kibbledistrict. The focus was discovered in 1991 by Adele and Walsh, who, given the proximity of the town ofKibble, called it "Kibble focus". The size of the focus is not lsrown, but it is estimated to be 100 sq Km. the average altitude in the area is between 900 and 1,500 m. A good roads network allows foi easy accessibility of the various points of the focus. The distict of Kibaale has 3 prefectures: Bugangaizi, Buyanga and Buyaga. Only the latter is onchocerciasis endemic; the population at risk is estimated at 70,000. The Buyaga prefecture is dividedinto sub-prefectures. Among these, onchocerciasis is found in Kagadi and (yânaisoke, which are watered by the river Mpamba, at Muhooro on the Nkusi and Ntengo rivers, and at Mabaale on the Mutungulu River. The rainy season is from August to November, and the dry one from December to March. For the rest of the year, the whether is sometimes dry or rainy. In a year of very good rainfall figures, the highest can go up to 1,200 mm. The hydrography of the focus is made up of perennialrivers. They run belou, the forest galleries, but remain accessible. They shelter the S. neavei breeding sites, which are productive all year round. The vector, at the larva stage, lives in phoretic association with crabs of the potamonautic. The zone is characterized by high vegetation. (elephant grass), and forest galleries along u,atercourses. Some forests are practically impenetrable. The area of the focus, previously sparsely populated, has seen the amval of several migrants. The latler come from the densely populated areas of the region to the West Nile (districts of Ara, Moya and Nebbi), and the valleys of Kigezi-Highlands to the southeast (districts of Kabale and Rukungiri) of Uganda. These two areas, the origin of the migrants, shelter onchocercal foci (namely the ioci of Wadelai, West-Niles and the forest focus of Bwindi), u,hich have high prevalence rates (56 to 80%: Nelson, I958; Mc Crae, 1962). The area meant for vector elimination is isolated, in principle, because the nearest focus is 40 Km arvay, a distance which is beyond the flying capacity of the S. neat ei. Besides, ivermectin has been distnbuted in the focus since 1992 by Sight Savers Intcrnational (SSI). 4.4.2. Nature of works No followed-up sun/ey rvas conductcd rn thc Mpamba-Nkusi focus before APOC activrtrcs. IIo\'1'1's1 . sotttc sourtdrngs takcn on tltc vcct()r (rrJcrrtrt1,, supl)orts of 1tr-..-intago stages), and thc Prcvalctlce ol tltc dtseasc (lLaprd lJpidcmrologrcal Asscssnrcnt. IlliA; skrn snrp tests) wcrc carric6 out rp thc 1990s. '[he oblectivcs of thesc rvorks wcre compatrblc u,rth thosc of the feasibilrty study approvc<i by ^l'}O(' to bc implcmenlcd rn thc Mpamba-Nkusr locus. Thc-y arc summeci up as follorvs: ? a33 Determine the identiÿ of the vector; Determine the limits of the reproduction sites of the S. neavei; Specify thc dynamics of the pre-imago and imago populations of the vector; Determine the natural vector charactcristics: infcstation rates, MTp, ABR, transmission indices. Collcct base hydrologic data; they are indispensable to the conduct of treatment; De termine the spraying points, and the frequcncy of treatment of breeding sites; Evaluatc the scnsibiliÿ of larvae to Temephos (dose, efficacious carrying capacity). 4.4.3. Rcsults obtaincd a) Prospecting of brecding sites . From September to December L999,45 breeding sites were prospected on the main rivers(Mplmba, Nyabwegyereka, Rwabutuju, Ntengo, Murungu, Mutunguru and Nkusi). This prospecting enabled the harvest of 688 crabs, of which 284 (41%) carried p.e-irnugo stages of tne S. neavei. Tlte crabs were highly infested on the Mpamba and Rwabutuju rivers, whereas thé load was average on theNyabwegyereka. On the Mutunguru, however, the crab population was very weak, and no S. neavei was harvested on this watercourse. , From January to November 2000, all the rivers of the focus were again prospected to determine the area of distribution of the S. neavei breeding sites. The captures and exÀination of crabs were donein accordance with the techniques of Mc Mahon (1958) and Raybould (1969). The results show that out of 623 crabs captured, 506 (8 t%) were positive, and the average number of larvae of the S. neavei, per crab, was 10. Taking into account a monthly distribution, the lowest load (5 larvae/crab) rvas recorded in June, and the highest (16 larvae/crab) in March. The most infested crabs were found in the Mpamba and Nyabugando rivers. The identification of harvested samples rndicates that the S. neat,ei rvas found everyrvhcre, except on the Nkusi river, where this species rvas replaced by the S. darttttosttLrr, Nkusi t1pe. The preliminary works are in their second year, and activities were essentially based onprospecting of breeding sites, and the choice of spraying points in the dry season. Thus, bemlen January and August 2001,642 crabs, of which 343 (53.4%) were infested, were harvested in the rivers of the focus. The most infested crabs were from the Mpamba River. b) Captures-Dissection-Transmission ln 1999, 399 females were captured between September and December at Sioni, a village located in the valley of the Mpamba River. The 167 parous females dissected revealed 35 (zl%)infectèa and 1(4%) inlective females. From January to November 2000, adult captures were also carried out at Sioni. Out of the 1743 females captured, a number of 524 parous ones were recorded, 126 (24%) infected, 243 (0.6%) infective ones, and 40 Lil1000 parous ones. As for the captures at Rurembo in October and November 2000, they helped to harvest 129 females, including 27 parous ones, l0 (37%) infected ones,2 (7.4%) infective ones and 111 Lil1000 parous ones. Finally, from May to November 2000 1484 females were captured at Nyabudango. The dissection of thesc females revealed 363 parous ones,99 (2i.3%) infected ones, l9(52%) infe ctive one s and 41 Lill ,O0O parous ones. , In 2001, captures \\rere also carried out at threc capture polnts of the focus. Thc ycctor charactcrlstics recorded at Sionr u,cre 33.9%o o[ parous females, 14.1y" ol infectecl ones, 2.79{r of- rtrlccttVc otlcs, a IVI'l'l) of l3 and 50 l-rl1,0()0 parous ones Ar I{urenrbo,26.5o^ olparous lc,ralcs ircrc observed, 20.4% olrnfectcd oncs,0.67u ol'infectivc ones.2l Lrl1,000 parous ones, and a M'll, cquaI to 28 was noted. Frnally, at Nyabugando, the resulls of transmission were 2l .B%of parous fcn-ralcs, lg.3% of infectcd parous ones,3.57o o[rnfectrvc ones,6l Lii 1000 parous ones, and a MTp equal to g6.Zyo. ? 34 c) Larviciding An expcrimcntal treatment session was conducted on thc Mpamba Rivcr in November 2000. 'l-his trcatment was preceded by prc-treatment data collection on the crabs, breeding sites of t6e .S. dutnnosturt s./, the water of the river (pl{, temperature, conductivity) and the fiow rate of the watcrcourse. Thc results of insecticide treatment indicate a reduction in infestation of crabs of the river,going from 66.7%to92-5%o. The same goes for the crabs enclosed in experimental cages placed in thc riverbcd, where thereduction rate fluctuates between 98.5% and 100%. As for the supports that shelter the S. darunosum s.l. or other Simulidae, they wcre all 100% negative, through the insecticide rvave. I{owever, the non-target fauna (trichoptera, leeches, water bcetles) was not affected. During the expcriment, the flow rate of the Mpamba river was 1, [ 26 m3/s, the water tcniperature was I9.2oC] and thc carrying capacity of the insectrcide estimated at 5 Km. The objective of the experiment conducted in July 2001 was to determine the effective carrying capacity of Temephos in the dry season. The Mushandikwa and Rwabutuji rivers rvere selected foi thË tests. Cages, containing 4 to 7 crabs bearing pre-imago stages of the .S. neavei, were placed in the rivers. The latter were treated with 300 ml (Mushandikwa) and 500 m, Rwabutuji) of Temephos. The post- treatment conhols, conducted 48 hours after spraying, revealed that the effective carrying capàcity(100% of mortaliÿ of larvae) of the Temephos was about 2 Km, for flow rates that could not be measured, since they were too low. d) Onchocerciasis prevalence Onchocerciasis is endemic in the Mpamba-Nkusi focus. Nelson (1958) and Mc Crae (1962) put the prevalence between 56' and 80%. In the valley of the Mpamba River, an epidemiological survey conducted at Nabwereba revealed 92%, ol oncho patients in the community (Ayele and Walsh, l99l). Prurit is recognized as being one of the most severe clinical manifestations oIonchocerciasis. ln 1995, the REA survey brought to the fore that the prevalence of nodules varied between 46% and 53oÂ. Except that in the region of Kagadr, the most affected villages were Nl,abrvereba (53%) and Soni (60%), whereas in the Kyanaisoke region, 46.7% and 30% of carriers of nodules were counted at Kanyabeebe and Mpamba respectively. c) Isolation of Focus The Mpamba-Nkusi focus has simtlar aspects (geographical, ecological) u'ith the sub-focus of Siisa rn the Babarole district. The preliminary data indrcate that the said focus is ecologically and geographically isolated. In effect, the S. neavei species rs practrcally the sole vector of the focus, for the S. damnosunr s.l. found are essentially ornithophilae (colbourne and Crosskey, 1965). Besides, the focus of Bugoma in the north is extinct (Walsh et al, 1996). [n the east, the Mutungulu Rrver only shelters a small quantiÿ of crabs, hence the absence of the S. ncavei. Frnally, the ecological conditions are such lhat no re-invasion can come from the east or south, except the u,est, where prospecting should enable the limits of the focus to be determined. 0 Training The implementation ol a control prograrnme, as planncd in the Mpamba-Nkusi focus, Irecessitates quahfied staff (high-level, technrcran and captors). The trarning of local staff on all technical attd practtcal aspects of cntomological evaluatton is ol utmost ncccssrty. Cer1arnl1,, an entomologist and lbur captors arc already opcrational, but thrs rs tnsufficrcnl to cover the entire locus. Personnel of the ltrvara locus (corn;retcnt and cxpericnced) could qrvc tcchnrcal strltport to tliat of N,lpantba Nkusi 4.4.4. CDTI status in Focus 1'he Mpartrba Nkusr focus is located rn tlte Krltaale clrstrrct. Thc total population ol thc crrdentic zonc ls 112,884 pcrgorls, wlttch is dtslrtbutcd ovcr 154 conrr.nurrrtrcs, ol rvhrch 136 are rn arr onchi_r 35 hyper-endemic zone, and 18 in a meso-endemic area. Mass treatment with ivermectin started in 1992, Ylllh" SSI campaigns. From 1994, I I1,154 persons were treated with ivermectin. I must be noted thaiCDTI was adopted in 1999, and the first distribution was completed in August of the same year, i.e. onc month before the start-up of the "vector elrmination" project. In 2000, the thcrapeutic coverage rate was 65% (63,841/98,816). This rate is74%o (832991112884) in 2001. The 4'r' phasc of CDTI in Uganda covers thc Mpamba Nkusi focus, and it is the second consccutive year that treatment is being financcd by APOC. Of course, the target population of thedistrict is known, but it is equally indispensable to determine that of the focus. tt,is precision would make it possible to monitor the progress of therapeutic coverage in the focus, and to r.s".. the impact ofivermectin on oncho transmission. 4.4.5. Budgct for vector elimination Activities To enable vector elimination activities to begin and continue, the APOC programme provided regular financial assistance, on the basis of letters of agreement (Contracts). fne LUt-e below sums up the financial component of the project. Covered pcriod Cash transferred to field (in US$) Amount spent (in us$) Purchase of equipment Total cost May.99-Dec 00 46,051 30,664 60,240 90,904 Jan.0l-Dec 0l 15,3397 NA 17,560 r7,560 Total 167,910 30,664 77,800 l!§r464 4.4.6. Discussions-Remarks _ The various prospecting activities undertaken in the Mpamba-Nkusi focus agree on the identiry of the vector causing onchocerciasis, namely the S. neavei. This species, given the ivorks conducted in 2000, is present all year round in the breeding sites of the focus. Its pre-imago population is the least abundant on the crabs between May and August. Of course the S. datnnorurr, thr- Nkusi ÿpe, is foundin the breeding sites of the Nkusi River, but the species is not anthropophilous (Colbourne and Crosskey, 1965).Theabundanceanddistributionofthepre-imagostagesofthes. neaveihelptodirectlarvciding, preferably toward the Mpamba and Rwabutuju rivers, which shelter the most infestàd crabs. The results of captures and dissection carried out between September 1999 and November 2000 show that in the Mpamba-Nkusi, the S. neavei is a good vector of onchocerciasis. [n effect, the number of infective females per 1000 parous females varies from 42 (Sioni) to 74 (Rurembo), while the tolerable line in the OCP area is one infective female per 1000 parous ones. The same goes for the number of infecting larvae per 1000 parous ones, which fluctuate between 40 and l l l, wheàas the acceptable limit is l0 Lil1000 parous ones. The vector characteristics (MTP; Nb Lii 1000 parous) recorded in 2001, are equivalent (even higher) than those observed in 2000. This means that the nsk is real for human populatrons living in contact with the S. neavei in thc Mpamba-Nliusi focus. Of course, the phoretic association with crabs limits the reproductron of black flres (number of bites/man/day, generaliy lower than 30). The fact sttll remains that these low densities are capable of causing inténse transmission. Transmission remarns high, despite the distribution of ivermectin. It must be saiJ that this phenomenon, observcd equally at Kicheche (district of Kabarole), was reported by several authors. The latter are unanlnlous in assertrng that ivermecttn does not intemrpt transmission, but partialll,. 'l'hc cxpcrrntctrtal trcatmcnt, whrch u'as car|rcd out on the i\41tantba l.\kusr Rrver rn 2000, brouglrt about a drastrc reductton in the rnfestatron (66.7%-100%,) of c.aÙs. It rvas the sarne lor 200 I, whe n thc treatnlcnt of the Mushankikrva and Rrvabutu-; r rivers causetl 100% of mortaliry of larvae o'er 2 Knl. Thrs result corroborates the observatron made in othcr foci (ltrvara, Sirsa, Asa), and indicates that tlrc Tcrncllhtls is the selcctcd larvicidc for ground trealrrent oIbrccclrng srtcs rvrt6 S t,rca,r,ei . Its cl'ficac' 36 and active carrying capaciÿ help to clean up the breeding sites after some treatment cycles. What remains to bc addressed is thc problem of dosage, in relation to the gow rate, and tlte number of spraying points. 4.4.7. Conclusio ns-Suggestio ns Thc expericnce gained by OCP in the arca of recording o[ entomological results, helped this institution to finalize excellent data collection forms. It is therefore preferable to use these forms, for thcy better report captures, identification, dissection and black fly infestation. These forms enable each person to verify and interpret results. The identification of samples that are harvested indicate that the black flies found in the Mpamba Nkusi focus are of the S. neavei and S. danutosutrt, Nkusi type. The latter, though classified as non-anthropophilous, needs to be better characterized, and its vector status well defrned. The kaining of local staff, which will guarantee the continuiÿ and efficacy of control activities, is of utmost necessiÿ. Staff will have to be tained on all technical and practical aspects of treatment with insecticides). The personnel of the ltwara focus, which is competent and experienced, could technically assist the Mpamba Nkusi staff. The biology of the.S. neavei, the success of the experimental larviciding, the extent of the focus, the geographical and ecological isolation of the focus, and the accessibiliÿ of the rivers in all seasons, are some elements that indicate that the elimination of the vector in the Mpamba-Nkusi focus could be undertaken with success. The problem that remains to be solvèd is that of insecurity, which, at any time, may impede the conduct of vector control activities. Despite the efficacy of larviciding, and the probable elimination of the vector from the Mpamba Nkusi focus, the dislribution of ivermectin will have to continue, to take into consideration the longevity of adult worm oIthe O. volvulus that are found in former patients. a I37 5. OVERALL CONCLUSTON 'fhis sums up the points pertaining to the training of localstaff of projccts, supervision of activities, andthc atLainmcnt of thc final objective of the various vector elimination projccts: - Thc expericnce acquired by OCP indicates that the implementation of a control programme, asplanned in the Tukuyu, Bioko, Iwara and Mpamba-Nkusi foci, calls for qualiiieipe.so.rnel. Enhancing training of this personnel is indispensable (especialty at Biokoi. Given the actual training needs in all the countries, measures need to be taken, not only in thé countries (namety the objective selection of candidates), but also in APOC (organizing training). - l-hc efficacy of vector elimination operations is lrnked to the continurty ip àctor control actions.fhe lattcr is evaluated, thanks to entomological surveillance. Thc OCF experience indicates that the supervision of activities remains the key to success, for it ensures quals in data collection. - It is' therefore, desirable that measures are taken to ensure supervision of activities (essentially entomological surveillance) conducted under the various vector elimination projecs. ThL coordinators of projects and APOC must play prominent roles. - The longevity (10-15 years) of adult O. volvulus worïns is such that the distibution ofivermectin will have to continue in all foci for at least l0 years. Even in foci where elimination activities are successful, distribution of ivermectin must côntinue, due to th. p."r".,"e of formerpatients (carriers of nodules). - The reports on the elimination of the vector in the different foci in Tanzania, Equatorial Guinea and Uganda, were an opportunity to assess the state of progress of eactr project. It clearly appears that the projects were undertaken on the basis of elements, such as the siie of the focus,its isolation, base data available, and the cost, as compared to CDTI. The only thing is that thepractical feasibiliÿ of projects was not sufficiently taken into account, and some faclors (actual limit of focus, accessibiliry of breeding site, risk of rc-invasion) were, at times, underestimated. Of course, when the vector is S. neavei,the factors mentroned above are *o." o, less attenuated,just by the mere fact of thc bio-ecology of the vector. On the other hand, rvith the S. dantrtosurrt s.1., the limiting factors become numerous: abundant supports, difficult accessibility to all breeding sites, black fly densities, which are generally high, high flying capacity. Ani yet a- 100% coverage of breeding sites is an imperative condition for vectôr elimination. Besiàes, it was agreed that in the selected foci, the elimination of the vector would be complete, definite and fast. This objective remains achievable for the foci of Itwara and Mpamba Nkusi. On the contrary, the reality on the field makes it mandatory to recognize that vector elimination at Tukuyu and Bioko risks having an objective that is too ambitious. It is rvorth recalling here one of the recommendations of the JAF6: if the meeting decides that vector elimination activities must cease in the focus, recommendations will need to be made to the country concemed, so as to enable it continue vector control in a national or brlateral context (cooperation). On the other hand, in the event rvhere activities will have to be continued, practical Àeasures must be taken by APOC for implementation, supervision and evaluation of treatment activities_ 38 6. AKNOWLEDGEMENT We arc pleased to thank here all thosc who in any manner enablcd tl-re preparation the current synthcsis on the onchoccrciasis vectors elimination activitrcs in somc foci of Cential Africa (Bioko inEquatorial Cuinea) and the East (ltwara and Mpamba-Nkusi in Uganda, Tukuyu in Tanza.ia). We would like to thank particularly : - Doctor A. SEKETELI, Director of the APOC Programme, for his trust on me bygiving me the analysis and update of the data of all kinds which are pertinent to decide on the possibilities and conditions of vectors elimination. I{ii experiencc and knorvledge o[ the various foct rvere vcry uscful to us in thc preparation of this document. Doctor M. NOMA who, with his remarkable knowledge of the foci and his availabiliÿ gave remarkable and efficient help. - Our work was carried out thanks to the assistance of many peoples (administrative and finance officers, secretaries, drivers) whose competence,, dlmamism and faithfulness are appreciated. ^ 39 7. 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In rcscarch and Control of Onchocerciasis In the westem hemisphere PAHO Scientific Publicatiort 2g8. S7-g5. Raybould, J.N-, ( 1969) - Studres on the immature stages of the Sirrrr/ iutn neavei Roubaud complcx and their assoctated cralls In the eastcm Usambara mountains In Tauz-ania. Investrqations In .r,cr.s Ancl largc strcants. Atrrtuls'of 'l'ropicul Alada<.tttc & Purusitolrgr,6-i. 26g-2g7 Sekctclr, A-, (200 1) - Broko veclor elinrinatton projcct: Comments and four marn qucstions about aerial campargn. 42 Teran, M. de.,(1962) - Sintesis geographica de Fernando Poo. Instituto de Estudios Africanos, Consejo Superior de Investigationes Cientificas, Madrid. Walsh, J.F. (1990) - Revicw of vector controlprior to the OCP. Acta Lindensia 59: 6l-78. Walsh, J.F & Maegga, B.T.A., (1996) - Planning of focal vector eradication [n onchocerciasis foci I1 Tanzania. Report to UNDP/IVORLD BANK/WHO Special Programme for Research and Training Ip the Tropical Diseases (TDR). Unpublishhed; Ii + 32 pp, Including Annexes). Walsh, J.F., Davies, J.B. & Clifl 8., (1981) - WHO Onchocerciasis Control Programme In the Volta River Basin. In Blackflies: the future of biological methods In Integrated control, ed M. Laird, pp. B5- 103. Londort/Neu,York: Academie. 309 pp. Walsh, J.F., (1985) - The feeding behaviour of Simulium larvae, and the development, testing and monitoring of the use of larvicides, with special reference to the control of Sintuliurn damnosunt Theobald s.l. (Diptera: Simuliidqe): a review. Bulletin of Entomological Research 75: 549-594. Wegesa, P. (1970) - The present status of onchocerciasis In Tanzania: a review of the distribution and prevalence of the diseas e. Tropical & geographical Medecine 2 2 : 3 4 5 - 3 5 I . Who, (1966) - WHO Expert Committee on Onchocerciasis; second reporl. Who Technical report series 335, pp.96. Wilson, M.D., (1999) -WhoiAfrican Programme for onchocerciasis Control Onchocerciasis vector elimination project (Bioko, Guinea Equatorial): Progress report. Wilson, M.D.,Cheke, R.A., Mas, J., Mc Call, P.J., Post, R.J. & Sima, 4., (1996) - Evaluation of the potential eradication of onchocerciasis from the Island of Bioko, Republic of Equatorial Guinea. (Who/TDR Project no. 050/181/34, Id 950612). Final report and supplcment. Unpublished report for Wto/TDR, Geneva. Wilson, M.D., Mafuyai, H.B. & Post, R.J., (1994) - Morphological Identification of sibling species of the Srmulium damnosum complex (Diptera: Simuliidae) from Nrgeria, Cameroun and Bioko. Proc. Exper. & Appl. Entontol., N.E.V. Atnsterdaru 5, I Bl-185. Woodruff, A.W., (1965) - The distribution of onchocerctasis [n Tanzania. ll/ho miuteographcd docuntent Wo/Oncho/32, 65. pp.3. Yaméogo, L., (2000) - Commentaires sur documents d'EIE sur I'rle de Bioko. 348/00/|/CU/ADM/6.1 a 43 a ANNNEXES: TABLES AND FIGURES 44 Table 1 : Captures and dissections at Lufilyo crater (TUKUYU - year 1g9g) Table 2 : Gaptures & dissections at Lwangwa masako (TUKUYU - Year lggg) MBR Morilhs Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 4 4 4 4 4 4 4 4 4 4 4 4 48 Captured 175 74 46 13 3 19 B4 22 a 7 12 35 499 Dissected 174 74 45 13 3 19 84 22 I 7 12 35 497 Parous 53 13 14 5 1 5 21 I 2 2 3 18 145 lnfected 16 3 3 0 1 0 0 1 0 0 0 0 24 lnfectious 0 0 0 0 0 0 0 0 0 0 0 0 0 Nb de L1 0 0 0 0 0 0 0 0 0 0 0 0 0 MBR 1 305 555 345 98 23 143 630 165 68 53 90 263 MTP 0 0 0 00 0 0 0 0 0 0 0 0 I Months Total Jan Feb March April May June July Aug Sept Oct Nov Dec Nb of days 4 4 4 4 4 À+ 4 4 4 4 4 4 4B Captured 1 0 0 1 J 112 222 201 62 7 26 0 635 Dissected 1 0 0 1 3 110 222 201 62 7 zo 0 633 Parous 0 0 0 1 1 19 63 B4 5 2 6 0 1Bl lnfected 0 0 0 0 0 2 5 4 2 0 0 0 13 lnfectious 0 0 0 0 0 2 0 1 0 0 0 0 3 Nb de Ll 0 0 0 0 0 3 0 B 0 0 0 0 11 B 0 0 B 23 840 1 665 0 1 s07 465 53 195 0 00 0 0 0 0 60 0 0 tl B3MTP 45 Table 3 . Captures & dissections at Tapio bridge (TUKUYU - year 1999) Table 4 : captures & dissections at Kambasegela (TUKUyu _ year 19gg) Months Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 2 2 2 2 2 2 2 2 2 2 2 2 24 Captured a 18 43 11 1 0 6 1 19 I 4 35 2 149 Dissected 1B 42 11 1 0 6 1 19 I 4 35 2 148 Parous 6 15 6 0 0 2 0 6 1 2 2 0 40 lnfected 0 1 0 0 0 0 0 0 0 0 0 0 1 lnfectious 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 lt Nb de L1 270 645 165 15 0 90 15 285 135 60 525 30 MTP 0 0 0 0 0 0 0 0 0 0 0 0 0 Months Jan Feb March April May June July Aug Sept Oct Nov Dec Total 2 2 2 2 2 2 2 2 2 2 2 2 24Nb of days( tured 1 2 0 J 0 3 6 14 3 0 25 22 79 Dissected 1 2 0 3 0 3 6 13 3 0 25 22 78 Parous 0 0 0 0 0 1 0 7 0 0 5 11 24 lnfected 0 0 0 0 0 0 0 1 0 0 0 1 2 lnfectious 0 0 0 0 0 0 0 0 0 0 0 0 0 Nb de L1 0 0 0 0 0 0 0 0 0 0 0 0 0 MBR 15 30 0 45 0 45 90 210 45 0 375 330 0 0 0 0 0 0 0 0 0 0 0MTP 0 0 Monlhs Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 4 4 4 4 4 4 4 4 4 4 4 4 48 Captured 24 72 220 281 228 409 328 228 202 182 13 43 2230 Dissected 24 72 220 277 227 407 326 228 200 180 13 43 2217 Parous I 15 56 95 61 126 113 140 50 16 2 18 701 lnfected 1 1 4 18 14 15 o 20 6 4 0 7 99 lnfectious 0 0 0 00 1 1 6 0 0 0 1 I Nb de Ll 0 0 0 0 0 1 5 13 0 0 0 2 21 MBR 180 540 1665 2108 17 10 3068 1 809 1710 1515 1365 98 323 PMT 0 0 0 0 0 8 28 98 0 0 0 15 149 46 Table 5 : captures & dissections AT Lufilyo crater (TUKUyu - year 2oo0) Table 6 Captures & dissections AT 2o0o) Lwanga-Masako (TUKUYU - year I Months Total Jan Feb March April May June July Aug Sept Oct Nov Dec Nb of days 4 4 4 4 4 4 4 4 4 4 4 4 4B Captured 1 1 3 36 198 470 405 524 79 90 7 1 181s Dissected 1 1 3 36 193 456 402 440 79 90 7 1 1 709 Parous 1 0 2 6 51 165 139 1 5 1 4 5 0 0 s24 lnfected 0 0 0 0 1 5 oU 2 0 0 0 0 16 lnfectious 0 0 0 0 0 1 2 1 0 0 0 0 4 Nb de L1 0 0 0 0 0 4 6 4 0 0 0 0 14 MBR MTP B 0 oU 23 270 1 485 3525 3038 3930 593 675 53 B 0 0 0 0 31 45 Jb 0 0 0 0 112 47 Table 7 : captures & dissections at rapio bridge (TUKUyu _ year 2000) Table 8 : captures and dissections at Kambasegera (TUKUyu - year 2o0o) Months Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 2 2 2 2 2 2 2 2 2 2 2 2 24 Captured 129 1 6 1 81 31 43 258 607 81 144 220 95 43 1893 issected 129 160 81 30 42 258 311 BO 143 159 95 43 1 531 Parous 49 53 19 12 10 71 115 51 47 21 6 o 463 lnfected 0 3 1 0 3 6 I 1 1 1 0 0 24 lnfectious 0 0 0 0 0 1 0 1 1 1 0 0 4 Nb de Ll 0 0 0 0 0 3 0 6 4 10 0 0 23 It 1935 3415 1230 465 645 3870 9105 1215 2160 3300 1425 645 MTP 0 0 0 0 0 45 0 15 60 207 0 0 327 Months Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 2 2 2 2 2 2 2 2 2 2 2 2 24 4 32 36 o 2 14 28 113 20 22 3 17 300 Captured I sected 4 32 36 I 2 14 28 113 20 22 J 17 299 Parous 0 5 5 0 1 7 B 33 4 6 1 7 77 lnfected 0 0 0 0 0 0 0 0 1 2 0 2 5 lnfectious 0 0 0 0 0 0 0 0 1 0 0 0 1 Nb de L1 0 0 0 0 0 0 0 0 I 0 0 0 I MBR 30 480 540 135 30 210 420 1 695 300 330 45 255 MTP 0 0 0 0 0 0 0 0 135 0 0 0 135 48 Table 9 : Captures and dissections at Bioko (april-may 2OOO) Table 10: Captures and dissections at Bioko (february 2001) Balacha de Riaba Barleycorn Musola Sampaka April May April May April May April May Nb of days 3 5 2 5 4 4 3 5 Captured 419 839 765 1717 345 182 331 540 Dissected 316 464 334 517 345 182 264 468 Parous 115 184 141 199 147 61 140 228 lnfected 5 5 13 4 18 7 15 18 lnfectious 2 1 2 2 I 3 2 5 Nb de Ll I 1 5 5 36 27 5 38 MBR 4190 5034 11475 10302 2586 1 365 3310 3240 MTP 119 11 172 99 6 270 203 63 263 Nb of days Captured Dissected Parous Parous infected Parous with L3 NbLi MBR MTP Sampaka I 222 106 49 25 3,8 5 56s5 319 1 't55 B9 23,6 19 9,5 6 Barleycorn 1 213 65 32,3 19 19 9 61 35 349 1 196 93 409 5,3 0 0 Musola Village 1 282 BO 48,7 179 7,7 35 9490 1275 1 340 96 61.4 22 1,7 1 1 327 92 46,7 25,6 0 0 Balacha da Riaba 1 118 69 33,3 8,7 0 0 351 0 1 116 B6 39,5 1 1,8 0 0 Riaba 1 359 65 26,1 0 0 0 I 038 0 72 1 333 BO 36,2 10,3 6,9 1 Granja da Musola River Musola 1 209 BO 30 8,3 0 0 4185 655 1 70 B6 64 14,6 7,3 26 Granja da Musola River Eba 1 149 60 43,3 11,5 0 0 4470 0 River Eba on road to Moka 1 123 80 32,5 19,2 0 0 2970 19 1 75 72 44,4 12,5 6,2 1 Moka at river Chuba Total tl 3293 5 1 304 60 0 0 0 84 300 0 268917 1 49 Tablell: Captures of simulies before and during vector control campaign BUSASA KIJURA Months 1994 1 995 1 996 January 312 827 0 February 262 333 0 March 484 720 3 April 672 9'19 2 May 624 450 0 June 500 430 1 July 260 187 Auq 449 1B 0 September 373 4 0 October 337 12 November 344 3 december 36s 1 Total 4982 3904 6 soGoHt Months 1994 1 995 1 996 January 96 19 0 February qq 7 0 March ÀaalLO 6 0 April 348 1 0 May 396 2 0 June 311 24 0 lqtv 123 J 0 Aqs 312 1 0 September 151 0 0 October 14 0 0 November 23 1 0 december B9 0 0 Total 2390 64 0 1994 1 995 974 743 0 632 s14 0 786 266 0 292 250 0 606 315 0 652 277 0 193 159 0 325 11 0 748 1 0 431 I 0 283 1 0 481 0 0 6403 2546 0 SIISA 199s 1996 148 428 1 187 387 16 740 316 0 111 .JJ ' 111 16 360 149 2 571 751 q 121 391 tl 217 303 2 104 10 1 72 4 0 44 2 0 26 J 0 2927 2855 49 1996 1994 50 Fiq.1 Tukuyu Onchocerciasis focus: Altitude range, dry season, S. damnosum larval habitats I,lt:.;fiùTU fit:i.i: i1r. Filt'triilf .Ô' AT"o"'! ti,?v /, qi':. : r ç,") A 't tn!' ,J i, 1û 15 20r"H J :3 v4 'rJ^ ,...1 ir. I Fiq.2: S. damnosum monthly biting rates (MBR) at four catching points in relation to monthly rainfall in Tukuyu focus, October 1998 to September 1999 lS:r'l lÈn:' l.{00 I ii:r.'l lrvJ) I tû0 ùx .r{}l lri{.r r € ; _1 d Uti È6 {I .-,1 I I ___ l Ehy.t\lÂr r I -Ô l-'Ynjr:t<IJl + ll-tflt1) :r - K:\_i:,:t.:1 1 t.1 'h-58 ,t{-!d (r:(-!€ f-r.ÿl FÉàee p5rÿl .Arr.ÿl ,.i}ï,1.3 l'l:flttÉ. 'r)1 1? lrl ,y; r,r}jt,ii, ,ira.]i i r_,H _ty U Y aÂLl St .E,ÿ I''IALAU I (]vÉ.r Ilald el t-.1'. Lrr{: 5.Û i0f '-= I 5l t: )u::a j7: r'. Iü, rv,{-e(a!":lnts s lt'P Cts\I!, t.l'É iEscs: Fcrs;u al -i:ïJ:À!leg àr-Ê -'€.lrk€tj.[.§,k( l{r{rû j.3 ]:"'1?f L . ,'l'lla f,æa'È ,r à-l -,t.\ l4uùl LEGEIIS: a 3 l:r.d1-nE :i:.crs Ci!rotcl gi-.--r: s tnt- icn I-lt'â:,aLer-rl :r I =L: : :f,.r .T I I I I \ I à 4 I .2 ? Li n "l5 51 Fiq.3: S. damnosum monthly biting rates (MBR) at four catching points in relation to monthly rainfall in Tukuyu focus, October 1999 to September 2000 ruxto 9000 8ffi 7ü,0 6000 5û00 40m lso 2000 l{rrl 0 I 1 I B § 6 E 5 I I I -,--l 0d-9'!) rtr-99 Oæ-91 ,bn-t» Fc§[O Ètür.00 Al7 oil t4T'm lùn rJ.l il--,]t, À,.IJ-l:r-r 5etrlr;l l,tcrÊJr. r:t I 1_i l 'snquafârr l ' -- vUrscxf-ll I r L'.Jrn rô I *--^rr) i +V!bC-+.t^] 350 lm Fiq.4: S. damnosum monthly biting rates (MBR) at Kambasegela catching point in relation to monthly rainfall in Tukuyu focus, October 1999 to September 2000 I.U I l1r. I I{: lltt l,!t E 250 ë{mo Ég ü 15û § IË roodà5 §so E R $rÀAll l---I- tr'tsR -I- ri 0 ftl-99 lùv-s0 Dn('99 Èn'00 Feb00 l'§r{o Apr-!û r4lv-fil .)-n-ül Jul-lrl Ar9 0'0 56'C0 / i' Hor{ltr I I Il E fig 5: 52 Annual rainfall in Tukuyu Focus, South West Tanzania Source: Chivanje Tea Estates Ltd: 1980-2000 w l$o sl0 15,''1 .F .L:tto J ! rr.t I lùïl S.10 Ë, .:iq: Fig 6 : Simulium damnosum s.l. breeding sites limits, dry season, 2000 ,t\ s1 -o-' ^-d .:d' {r- s' d' +d r*C d +*.*S rC -*".a,?'.,e,É' t,ûth{IÀl}{i \ Fp0R I I I "r+;, ,,I II I l-- +or. "4/\- - - '4rrn: l,:! --* hiY Àt, tt I ( I l(rn ;tI __l I I I I I I I I tI I I I I I I I I il I 53 !!g,Z : Capture mensuelle sur les rivières Lufilyo, Kiwira et Mbaka (Tukuyu) 1200 r000 - a- KIWIRA -#Mb*e - -Lutïp 4 /1 I1/1 I1 I1/1 I1 !lo tIl,*tt Ê E .00 /\\ \ saêpEtnrri 2&(.6rs / \, tJ/" I \ \ / r'\ WEEK 01 \\ \./\ \ .2" \ /-- \.200 0 Tukuyu focus vector elimination project Insecticide dosing points AINS ffi. RLrr.lS\,iË' ) o jrru41 FEV H F§ AVRIL hlAl JUIN JUIL AOUr SEPT OCT HOV OEC irffid2 Fis.8 r =r 3 /"1PoR01 L JJ krY r-u 4d: li,tÏ.tÊ Êla llte 5 BuJaNfà Êe -- ae - ne+tJFfrFgi Ir. L., !zê= K.it^ LÔâilf,, f'r L' ,ïô = nqrrP46e RV l-' 1êû : nulltl'tJüfÊa À.p; gp : trÇog_o Êv_ ri ?Èr r lJi èm§t Rv tt9 iæ = krfrair6E Êu :u 1@ = krl.E64 eu.ù 1rù j n gutr 4,. I - - "r ?'l5S .......,i Bord€r ('tr.[ltr ÂiClfcula a Bi Clrcüia B qi(:ircùti C a)?l:arrotqd t,TrÊrled IGY - e;- 05t: ,. ) l'.i \ \ D !. Fiq.9 Fiq.10 54 Tukuyu Focus vector elimination proiect lnsecticide dosing points HOUNTAINS MT. RUN6\üE .,' WEEK 02 to 06 kÊY fu4ars ÿlftE â* l$ re = 8Lr+Jb Rr. ru 6o ' rltttllhFrÊ suL!7@: krÊ{t{ânâxg ft 14, too = Fl!urxû(&.r^ Êu[r lor : nltrlr{-tJdgE'rr Ê! t<r So: NCqS Êÿ. kT 1ü . luYÂnltf ev ,Yf 5ôo = kt(,trr{È.Rv,Lu ls r khue{ Êu.w î1@: HgUlJ Rt. !- .: =E ! M n (é _,_,- e.t5.!. ç t I ',--..-,. Bordrr Clrtult{ AtCirs!il,A-. gl Ctrcr( I (1. Circull C Ç l-lnlrcrte* ' J O : TretcaY ___ _ 1"r5' j t_,: A\{l ..:.,r ,----,lcL. 05 Tukuyu vector elimination proiect Prospection map Hï. RUr,r6V/E POROl Y{EE(01 __- - KEL 0 id: iîftE R\t i!'IÉ ' BuiNiD q!. ru 6F' -r^!JrylÈÊ. t L, Ta : klPÀ^,${mM e l-, 9s. = IiHzrPÀ6aU Ê L! 9É! : i1BLt,-|,ltsËH k: ID : Nûo;b Ru r q@ = iiyênsl Rr ,!i s+ = i«êeriét çvLv iq, : (trLE6+ Ê,r! .1È: :âL.]l, â1 V)l-I 5 !' è = .,.) Â1 ri Cirsuli A Cirrüll B Bo.dcr Clraùltr ':Ç C, Cirsull C - , Poriti!'e S{tt§ r ! NtBatiÿc §it€t t'I ,t_.\t ( l\ - n[, -r> ed,itrx"Èr.rrüi mfi.&ù ..Él0 lS l0 (ao ttsrora*Èr{f' -l i'15 D a kEY 'r. i -- Rird ( æ P*l-qrv" SÊ.,Eni :mtu{r0À ts-......-..+o s to ts lbxa O hraoox m.,,* Airr , ,!t Fis.11 Fie.12 55 Tukuyu Focus vector elimination project Prospection map ,t'1PoR Sr WEEK 02 !o 04 kEY L r*s ttEL8 Êv p 5æ " 6rrAV!6 Rv. Lu é@ , iw*(LIâAFr a r ù T§ = ktR^ ilüârsno Pr L.r Eæ = llur{r,Êa5^g ç irJ îtu -- n$A[r,J-ü{cÈ!. i,ü tæ: ÏuieE Rv. aÎ tJ = lÿYêrlrft Êÿll8 }oo = h&4il6Ë ÊvLu 1æ = l(À{16+ Êv.u lrôo = È1&(U ft. I MÏ. EUNGWE .,v1 FE 5 E = 1 I @ t!F Ç ,,...., i ÛôrdfiClrculs ef cttcor ,1 sf circut tl ci ctr(ult C -i Poslrh'cslric - ; NeSstiva Slln e'Jc 5 t a. KEY 0 t r0 r5 ?0,(n \_- ! rui -1, A\{rHA - Pif, :-.t Êal"iatænSrrrun WEEK 05 to 06 ,. t.. ' ,',,, L: -kÊ Y Lu +*,= lilttÈ Pÿ, t!,-ê = SLjJ4{§ü Êh!, éæ : i-i 4[srl(lÊfr I r. fd-- krPatl{tÂnÀtr, P L æô: i]Ar)fAÉaU tr l{r ,.r : l:utl')4-/û9&'a !f, gco . lvÉ?J-§ pv ^3 (7'i . t-,YÊnrJt R!ÿ t'o = kl6A,tlrs Fr. L" rS'I I .É' Tukuyu Focus vector elimination project Prospection map HÏ. (ô n POROl I V) FE 5)ÿ = Lu ts: kuLÈC^ t a ...,.,. : 8ôrdtr Clrcqllr {:CircÙit r\ rtl Circvlr I C: Cir.ull C : - : Polrtirù sitÈs -:NrgrtircSitcs c'i; 4 Ç) IGY JtÉ9fl'ta&i 05 r0 15 l0 Ko ,: MAIAWI '"t. 56 Fis.13 : Monthly rainfall (mm) at Malabo in 1991-95 & January-June 1996 Jen FËb liar AD.ll May Junê July Aug MONTH OF YEAR Sept Oct Nov Dec Fie.14 : 700 000 F00g J lloo 2 E*o J F P.oo t00 +t8rt +1992 +1903 +1914 +10e6 - o- 1906 0 Bioko Island ri,, ... f," i l I I B t , a i',: ) I ri' 57 tr'ie.l5 : Monthly biting rates (MBRs) at the River Sampaca in1992 8000 70oo 6000t!( EBooo(, zÊ Elooo à Êsooozo =2000 1000 0 &1É-: Monthly biting rates (MBRs) at the River Timbabe in 1992 lu)00 3500 Jan Feb MalApril Msy June July Aug Sept Ocl Nov Dec MONTH OF YEAR May June July Aug MONTH OF YEAR I ! I 3000 u,l Izeoo2 82000 a{!eB 16100 1000 600 t zg 0 Jan Fcb illar April Sêpl Oct ilov Dec I r [Bâr F 58 Fie.17 Onchocerciasis foci in Kabarole district B sffimFÉs : ? First treatmentÊ of the Sogohi river p ..,,., 8tref d(.ôq@a.M zAl'nE !:.29 Fiq.18 : Number of ,Sinulium neavei caught per day (1994 to 1996) at four catching sites t 1an = ruu =eo (dü rÂno ,r" û O ,^ = o -. ?a) VY V xt I lll v vll ix xi I I;l Months January 1994 to December 1996 ilvvll lx V VII IX X; Catching site: -.-e- Busega a Kijura '- Sogohi r I ____t -æ I, ! ....' a I t

It AFRICAN PROGRAMME FOR ONCHOCERCIASIS CONTROL (APOC) ORIGINAL: FRENCH OVERVIEW OF THE STATUS OF VECTOR ELIMINATION PROJEGTS Prepared for APOC by Prof. S. Traoré Temporary AdvisorMHO/APOC t APRIL 2OO2 PLAN EXECUTTVE SUMMARY........... .................. t 1. TNTRODUCTTON .................... 1 2. NOTES ON ONCHOCERCIASIS lN AFRICA: VECTORS-DISEASE-CONTROL. 1 3. FOCI SELECTION CR1TER1A............ ....................4 4. PANORAMA OF SITUATION IN FOCI... 4. l. TUKUYU FOCUS................. 4.1 .l . Presentation of focus 4.1 .2. Nature of works 4. I .3. Results obtained 4.1.4. CDTI status in the Tukuyu focus......... 4.1 .5 . Budget for vector elimination activities 4.1 .6. Discussions - Remarks ................ 4.1 .7 . Conclusions-Suggestions .............. 4.2. BrOKO FOCUS.... 4.2-1. Nature of works.... 4.2.2. Outcomes obtained.... 4.2.3. CDTI status in the focus......... 4.2.4. Budget for vector elimination activities 4.2.5. Discussions - Remarks 4.2.6. Conclusions - Suggestions............. 4.3. ITWARA FOCUS 4.3.1 . Presentation of focus 4.3.2. Nature of Works 4.3.3. Results obtained 4.3.4. CDTI status in the Focus........ 4.3.5. Budget for vector elimination activities 4.3 .6. Discussions-Remarks 4.3 .7 . Conclusions-Suggestions .............. 4.4. FOCUS OF MPAMBA-NKUSI .............. 4.4.1. Presentation of focus 4.4.2. Nature of works 4.4.3. Results obtained 4.4.4. CDTI status in the Focus 4.4.5. Budget for vector elimination Activities... 4.4.6. Discussions-Remarks 4.4.7 . Conclusions-Suggestions .............. 5. OVERALL CONCLUSTON ....37 6. AKNOWLEDGEMENT 7. BIBLIOGRAPHICAL REFERENCES 4 4 4 5 5 ) I ............ t0 ............ 10 ............ 1t ............ 13 ............14 ............14 ............15 ............2t 22 22 24 26 26 27 27 29 29 30 30 32 32 32 33 34 35 35 36 38 39 t It EXECUTIVE SUMMARY I. INTRODUCTION In most of tropical Africa, human onchocerciasis or river blindness, a dermalfilariosis, caused by the parasite, Onchocerca volvulus, is still a serious public health problem. The parasite is transmitted to humans by the black fly, Simulium damnàsum s.l . The AfricanProgramme for Onchocerciasis Control (APOC) was established to control the disease through control of the parasite populations, in African Countries, outside the operational area of another onchocerciasis control organization, the Onchocerciasis Control programme (OCp) in West Africa. APOC's Strategy is Community Directed Treatment With lvermectin (CDTI).However, in some isolated foci at Tukuyu in Tanzania, Bioko in Equatorial Guinea, Itrvaia and Mpamba-Nkusi in Uganda, APOC has also initiated vector elimination activities duringthe past least three years. Following recommendations of a mid-term external review ofAPOC's Programme, principally, the action plan for phase II and a phasing out period, theManagement of APOC has decided to convene a meeting to critically .iri"* the vector elimination activities at all foci. As part of preparations foi the meetiné, *" provide here a synopsis of progress made at each of the vector elimination considered focus. 2. TUKUYU FOCUS The Tukuyu Focus located between the Tanzanian and the Malawian borders covers an area of about 3000km2. It is watered by three river basins: Kiwira, Mbaka, and Lufilyo. TheSongwe river, a main river bordering Malawi lies outside the focus. From WHO estimates in1995, about 650, 000 people in the focus have onchocerciasis; but the exact figures of endemicity are yet to be known through a survey. Ivermectin distribution started at the focusin 1994 and the CDTI, with a therapeutic coverage of 660/o, is going on satisfactorily. A synthesis report of Maegga (1991) indicated that between 1976 and 1997 several random transversal entomo-parasitological surveys were conducted in the Tukuyu focus. However,Since October 1998, the surveys have become regular with technical and financial ,uppo.tfrom the APoc programme. The results obtained are as follow: Breeding periodicity of Simulium: Studies conducted during the l9g0s and 1990s(involving Walsh & Maegga) agree with earlier ones, conducted in the 1970s and early 1980s (by Lebene and Guillet) that ; there are larval stages of Simulium stages of Siruuliunt damnosum s./ in the three major river syste.nr i, the Tukuyu focus. studies carried out by a national team during late 1998 and early 2oo2 revealed that; out of 85 breeding sites visited, simulidae were present at 46; 34 of which had S-damnosunt s.l. Observations made in 2002 also indicated that ZZ of 49 river breeding sites visited had aquatic developmental stages of Simulium while 9 out of 21 tributaries were also positive. Cytotaxonomic identification has confirmed that the Simulium c{amnosarrn species in the three main river systems within the Tukuyu focus is S.damnosum kiwira type(l 419 I 1479 Simulidae). Onchocerciasis transmission in the area has been indicated to occur during tlie dry seasoll based on occulrence on high populations of bitting females during the period. However, this observation must be treated cautiously b""ru." it is not certàin fly catchers have followed the standard protocol exactly. I ! uSensitivity of S.damnosum s.l at the Tukuyu focus to 2O%o temephos was put forward by Guillet (1981) and later confirmed by Barro (1999-2000). The LC95 has been determined to be 0.66 mÿl and 0.384mÿl îor low and high mortality rates respectively. Tests in rivers indicate that for a discharge of 4.3m3 /s and a dose of 0. I mg/l, the effective carry for (100% of déchrochement) of temephos was 7,060km. Bt had a maximum efficacy carry of one km. Analysis of annual distribution of simuliidae populations and density enabled Pederson and Maegga to conclude that tlie dry season (June-November) would be the ideal period for larviciding, as accessibility to breeding sites at that period would also be easier. The first ground larviciding took place between December 2001 and February 2002. The three main basins of the focus were subjected to a weekly larviciding using temephos at the dose of 1.33mÿl for 6 weeks. After the first week, no breeding site on the main rivers visited proved positive. Geographically, the natural barriers surrounding the focus (Lake Nyasa , mountains), initially, created the impression that the focus was isolated. Then in 1981, following a series of surveys including that of the Lumbira and Songwe rivers, Guillet concluded that the focus was not as isolated as previously considered. However, based on cytotaxonomical, entomological and epidemiological studies, the Tukuyu focus was declared isolated. Nonetheless, the data obtained in 1996 showed that ,S. damnosum s./. thrives downstream of river Songwe, the natural border between Tanzania and Malawi . Moreover, in the south west of the focus, a few kilometers from Lumbira, is the large and perennial river Kilando which could also harbour S. damnosum s. l. With the Kilondo and Songwe rivers located outside Tukuyu focus, it is not likely that the focus is isolated. Based on the different results, it could be deduced that tlre present distribution oî S danmosuru in the Tukuyu focus notably during low water level period is yet to be established. Some authors assert that the Tukuyu focus is isolated . Others, based on the proximity of the river Songwe and its tributaries and the presence of S. datnnsum s.l in some of them are cautious. It is therefore important to conduct an entomological re-assessment in the Songwe basin in Tanzania and Malawi. In addition, to accept or reject the hypothesis of potential reinvasion of the treated area by S.damnosurn from outside the focus, it would be necessary to undertake a vector identification in areas concerned. 3. THE BIOKO FOCUS The Bioko Island, a massive volcanic land covering20lT km2, is situated in the Gulf of Guinea off the coast of Cameroon and Gabon. Its watershed is made up of small rivers with Iow discharges which take their sources from mountains. The epidemiology of onchocerciasis is the forest type with an average prevalence rate of about 75oÂ. For CDTI, the target population is estimated at 60,000 people and the therapeutic coverage was 42Yo in the year 200 1. Studies on the onchocerciasis vector on the Bioko island starled in 1989. A TDR feasibility study on vector elimination in this focus was carried out in 1996. In 1999, various additional studies were conducted through APOC funding. The results obtained led to the following : - The southem part of the island, about 40% of total landarea is inaccessible. However, many surveys have been carried out in the accessible zone. The results indicate that the '5. darnrtosuttl complex is represented in the Bioko Island only by the Bioko form t a ? )ul oî S. yahense. The rivers are many, short (7km long on average) and protected by aluxurious vegetation, rendering the numerous rivers inaccessiÙlé. In tt " dry season, the discharges of the rivers generally fall below lm3/s and they are cleanind cool(turbidity < 5JTU) ; (l9oc<temperature<26oc) water. No piéimaginal stage ofS.damnosum was collected above 500m altitude, while, some aàult, *è.. captured at altitudes between 55Orn and 1250m. The authors were unanimous on the fact that the Bioko focus is isolated. In fact, it is an island where weather conditions including wind movement: have been considered to negate re-invasion of the focus. Additionally, cÿotaxonomical, morphological and cÿogenetical obviousnesses lead to the recognition of the fact that th; ^S. yihens" inBioko is different from the standard type. There is therefore a consideied genetic isolation compared to the known simuliidae species and those found à, tl.reCameroonian coasts. - It has been observed that apart from the dry season (January to April), the simuliidae population densities are not significant. On the contrary, MBR betwéen 1305 and l1 475 has been recorded in April- May and between 2970 and l0 380 in February. This means that even in the dry season , the simuliidae population density can be high. - In 1996 the dissection of 56 females helped to record up to 14.6% of infectious females. In 1999, the dissection of 878 femates revealed 44yo infected and gyo infectious females. Despite the fact that, the ATP has not be established for the year 2002' the MTP obtained in April and May at the various collection points *".. Àigh(MTP minimum :130 in Balacha; maximum : 473 at Musola ;. it tras also beenindicated that apart from collection points located at high altitudes (0<pMT<72), alt the others MTP are located between 319 at Sampaka and, lZ75 at Musola. Various studies of agree and indicate that transmission is significant on the Bioko Island. - Results recorded in 1989 and 1998 show that after 9 years of ivermectin treatment, prevalence has drastically changed from hyperendemicity (74.6%) to hypoendemicity(38.6%). Such a shift should be reflected by simulium infestation.'Thus, from 1993 to 2002, the number of infecting larvae for 1000 pares droped from 400 to 74 and MTpfrom 1600 to 15. However, the infestation rate recordedàuring 2001 does not seem tobe affected by the use of lvermectin: MTP between 319 i;Sampaka and 1275 at Musola. - The first ground larviciding compaign took place in Bioko during 2001 dry season. During the period of the exercise, only 30 rivers had enough watei flowing to enable treatment. Hence, out of 248 proposed treatment points selected, onlÿ 92 were retained. The selected insecticide for ground larviciding was temephos at the operational discharge dose of 0.4 litres/m3/s. The treatment, which lasted five weeks was carried out once a week from February l}'t',2001. From the numerous data collected, it can be retained : ' The carry of the insecticide was between I and 3 km for discharges ranging from 0.05m3/s to 0.2m3ls. I'hc life span of tlie preimaginal stage of Sirnuliurr was rather long (rnore than two weeks) becausc water temperatures were usually low ( from l9"C to 24"Ci. The recolonisation ofbreeding sites after each treatment was therefore very slow. t t lv Adult population density feel sharply after the commencement of the treatment. Fly catching was nil at some points after only four weeks of treatment, although rivers were not totally treated. At the structured operational dosage, the number of chironomides was reduced however, repopulation was relatively fast. On the other hand, fish and shrimp populations were not undurely affected ( no mortality, normal behaviour ) by the larviciding. At the end of the first exercise which took place in the north of the island, expert consideration indicated that due to inaccessibiliÿ of some rivers, ground larviciding alone cannot eliminate the vector from the Bioko focus. This objective could however, be achieved in a one single season through combined ground and aerial larviciding. However, as authorities stated, the use of helicopter for the exercise should be indicated by proper answers to some questions. Such as : what is the impact of twelve years of ivermectin distribution on the simulium capacity to transmit the disease? What is the cost of the aerial operation advocated ? How many people will be protected through this operation? Reference to the target objective, which is to eliminate the vector, various results obtained in Bioko, indicate the following : The geographical location, weather conditions and cÿotaxonomical, morphological and cÿogenetic criteria confirm that the Bioko Island is isolated. Based on the distribution of the rivers and prospected breeding sites, it is evident that each survey, would reveal at least a new breeding site (discovered in a river already itemized or not). Moreover, the presence of the adult vector in high altitude is a reinvasion risk factor for a treated zone. This situation impedes the total coverage of breeding sites by through larvicidings as a must for the vector elimination. 4. Itwara Focus At about 25 km north of Forte Portal, Iies the Itwara focus surrounding a forest reserve that bears the same name. Hydrological conditions are generally conducive all year round for the development of the Pré-imaginal stages of S. neavei. The breeding sites are mainly located on rivers Sogohi, Siisa and Aswa. Onchocerciasis is highly endemic in that densely populated zoîe. The Itwara focus community and its sub-foci (Siisa, Aswa) are isolated from the other onchocerciasis foci. The nearest focus being about 100km away and mostly infested by S neavei whose flyrng range does not exceed 10 km (Garms, 1997.) ln the 1970s, the use of DDT, emulsifiable concentrate at 25o of active ingredient disrupted the transmission of onchocerciasis in the ltwara focus (Garms et al., 1994). Due to lack of funds and insecurity, the control was interrupted from 197 5 to 1977 . However, in 1990, a new funding jointly provided by the German Cooperation Agency (GTZ) and the Ugandan Ministry of Health made it possible for data collection to continue. In this connection, all the rivers likely to harbour S. neat'ei s.s were surveyed and the adult population of S. neavei studied through fly catchings, dissections and determination of infestation rates.'fhe larviciding of temeplios carried out from August 1995, proved to be effective with promising results after only three larviciding cycles. In fact, between I994 and i i a Iv 1995, the simulidae density dropped from 481 to 0 at the Kijura bridge and from 365 to 2 atBusasa. Considering the results obtained, larviciding were extended to the major breeding sites for S. neavei in the focus. The entomological data collected between 1991 and 1994 prior to the treatment withtemephos indicate that38.90 of crabs captured in the river Sogohi 1lt*u.u focus) carried thepréimaginal stages of S. neavei. Results of various surveys tally and show that treatment of breeding sites withtemephos drastically reduced the S. neavei preimaginal population irrespective of the focus orits sub-focus (Siisa, and Aswa). Even when treatments weie discontinuàd, low densities were recorded' Post-treatment controls in the Itwara focus revealed that since i997, infested crabs are nearly absent. The same is true, since year 2oo}, in the Siisa sub-focus. Be'rween January and August 2001, surveys conducted by the national team have made it possible to catch 4656 crabs in the Itwara focus, with the breakdown as follows: 948 in Itrvara, 630 in the Siisa sub-focus and 3078 in Aswa sub-focus. No préimaginal stage was discovered on the crabs fromItwara. Only a larvae was detected on on. "rib 1i.e. o.zN of population) from Siisa. Thehighest percentage (0.4%) of crabs showing positive were noticedin Aswa. ' From the beginning of treatments in 1995, the S. neavei population density hasdropped, reaching the zero mark in 1996 atKijura and Sogohi. As the tàatment went on, thetendency has intensifted because no biting female *"r "uptu. ed in ZOO2 in the entire focus(ltwara, Siisa, Aswa). Results recorded in 2001 confirmed the absence of bitint females in the zone' It is worthy to note that prior to the treatment with larvicides, the simuliidae populationdensity was 19,000 bites per person and per year. With the current situation, vector elimination activities in the Itwara focus and its sub-foci (Siisa, Aswa) can be called a success. It is likely that children bom since the beginning of operations would no longer be carriers of the micro-filaria. However, ivermectin distribution should continue due to the longevity of the adult O. volvulus worïns carried by old patients. 5. The Mpamba -Nkusi Focus The concemed vector elimination area, covering a landarea of 100 km2 lies in theNorthern part of the Kibaale District. The district is madi up of 3 prefectures but it is only inBuyaga prefecture that onchocerciasis is endermic. The population at risk is about at 70 000with a prevalence rate between 58o and 80%. Therapeuiic coverage was 74yo in 2001 in theKibale District. Perennial rivers with breeding sites fàr S. neavei all the year round constitutethe hydrography of the focus. During surveys for larvae carried out in Lgg9,28 (41%) crabs out of 6gg were carriers of S' neavei Pre-imaginal stages. The same data for the yeàrs 2000 and 2001 were respectively s06t 623 (8 1 %) and 393 t 642 (s3.4%). Characteristics of female vectors recorded at Sioni were as follows: 33.9% pares; 14.7oÂinfected, 2-7o infectious; MPT from 13 lo 50 Lil1000 pares. At Rurembo,26.50 pares20A% infected,0.6% infectious,2lLil1000 pares and PüT value of 2g were obtained. AtNyabugando, transmission rates were'. 27,8o/o ienrelles pares, 18.3% infected pares, 6l Lil1000pares and a PMT value of 86.2%. A pilot treatment exercise was carried out on Mpamba river ip November 2000. This rcduced tlie infestation rate of crabs tiving in the river lronr about 66,1yo to 92.50Â. VI The same was true for crabs confined in experimental cages and placed at river beds where reduction rate ranged between 98.5% and 100%. S.damnosum and other simulidae breeding sites were all negative after larviciding. The non-targetted fauna (trichopterre, bloodsuckers, water scarabs) were not affected. During the experiment, the dischaige of Mpanrba river was 1126m3/s, with water temperature reading lg.2"C and insecticide-carry estimated at 5km. The experimental treatment carried out in 2001 on Mushandikwu ,nà Rwabutuji rivers also showed a drastic reduction in crab infestation (100% mortality rate over 2km.). To conclude, the following must be noted ; Sampling conducted indicates that the simulium flies in the Mpamba- Nkusi focus are ,s. neavei and S damnoswn, Nkusi type. Even though considered non_ anthropophile, the latter species' characteristics and its vector status must be well- defined. The biology of S neavet, success chalked by the experimental larviciding, extent of the focus, ecological and geographical isolation of the focus and the all-weather accessibility to rivers are factors indicating that the vector elimination exercise in Mpamba-Nkusi focus can be carried out with good chances for success. The problem of insecurity which, at any moment could slow down or even impede the conduct of anti vectoral activities is yet to be solved. Despite the efficiency of larviciding and probable etimination of the vector from the Mpamba-Nkusi focus, Ivermectin distribution should continue considering the longevity of the adult O volvulus worrns present in previously infected persons. GENERAL CONCLUSION The presentations on vector elimination in different foci of Tanzania, Equatorial Guinea and Uganda provided the opportunity for assessing the progress made in each project. It is very clear that the projects were implemented on the basis of factors such as focus iize, its isolation and the availability of baseline data. However, project feasibility was not given enough consideration and some factors (actual limits of the focus, accessibility to breeding sites, reinvasion risks) were sometimes underestimated. With the S neavei vector, the factors enumerated above do not always pose problems due to the bio-ecology of the vector. However, with .ÿ damnosum s. /., the limiting factors keep on increasing: many supports, difficult accessibility to all breeding sites, generally high simulidae population densities, high flying capacity. Total coverage of breeding sites is a sine qua non condition for the vector elimination. Moreover, it was understood that in the selected foci vector elimination would be complete, definitive and fast. This objective remains achievable in the Itwara and Mpamba-Nkusi foci. On the contrary, what actually comes lrom the field compels us to admit that the vector elimination in the Tukuyu and Bioko foci could have been a very ambitious objective. We should be mindlul of one of the recommendations of JAF6 that if the meeting decides to stop the vector elimination activities in the focus, recommendations should be made to the countries concerned to enablc tliem to continue fighting the vector in a national or bilateral(cooperatiott) context. In thc case where activities should be pursued, some conveniept arrangenlellts sllould be taken at the APOC level to execute, supervise and evaluate the larviciding activities. t ! 1. INTRODUCTION onchocerciasis is a human disease caused by a nematode filarial worrn, onchocerca volvulus,transmitted to man by the Black Fly Simulium. 'Ihe disease which is manifested by skin lesions, visual imperment and blindness is still a major public health problem in most part of tropical Africa.As at 1996, this endemic disease affected 17,5 million people, out of whom tS mittion (gSyr) lived in countries outside the Onchocerciasis Control Programme (OCP) area in West Africa. The AfricanProgramme for Onchocerciasis Conhol (APOC) was therefore designed to control this criticalparasitosis in regions that were not covered by the OCp. The overall objective of onchocerciasis control is, usually, being able and in a sustainable manner' control the endemic disease, though the final objective set by APôC is the elimination of thcdisease, as a serious public health problem, and an obstacle to socio-èconomic develofment in Africa.The strategy adopted is the Communiÿ-Directed Distribution of [vermectin (CDTI). However, since the launching of APOC, vector elimination projects have underpinned theCDTI in some countries. These projects, which are approved by ihe-Committee of Sponsoring Agencies (CSA) and ratified by the Joint Action Iorum (JAF), are ongoing in Uganda (in the foci ofItwara and Mpamba-Nkusi), Tanzania (foci of Tukuyu), and in Equatoàat Cui.,"u"1foci of Bioko). The control strategy applied in all these foci has been control of pàpulations of thè disease vector byground larviciding aimed at elimination of the vector, and consequently the disease. The APOC programme undertook these vector elimination activities on the basis of elements such as the size and extent of isolation of foci, base data available, and the cost of operational campaigns. Besides, it could be said that this ÿpe of control has several positive aspects: rapidintemrption of transmission, no consequences for the environment, and in principle, and the definite nature of control effects. At the outset, therefore, the understanding was tirat th! eiimination of the vector in the foci would be total, definite and fast. The acceptance and financing by the APOC progmmme of the various vector eliminationprojects were spread between 1996 and 1998. To date, at leàst three years have elapsed, and it is worthknowing where these projects stand. This concem was expressed in 2000 by thË faÉO lf.ogrammeexternal review), which, in one of its recommendations, authorized the manage-"n, of ApOC to organize a meeting charged to determine the Programme strategy for vector efmination fo. tt e ziùphase of the said activities. This meeting was to call on all the expertise (namely, participating countries, APOC OCP, TDR, TCC and all resource persons). Besides, in the àir"r..-io.,., particular attention would be accorded to the impact of ivermectin (CDTI, CBTI)) on the epidemiology andtransmission of onchocerciasis. The JAFT came to determine that no new vector elimination lioiectwould be undertaken during phase 2, and during the withdrawal phase of APOC. It also confirmed that the current activities would be cntically reviewed at the beginning of phase 2, in order to decide on the continuation of the projects. In line with the recommendations made after the mid-term External Review of the APOCProgramme, as well as on the basis of the Plan of Action for phase 2 and the gradual withdrawal ofAPOC, management decided to hold the vector eliminatron review meeting in ApOC countries in May2002' It is, therefore, wtth respect to the preparations for the said meeting, that this surrrmary tries to note the progress made, since the start-up of activities in each of the foci. 2. NOTES oN ONCHOCERCTASIS rN AFRICA: VECTORS-DISEASE- CONTROI,. The disashous consequences of ocular signs of the onchocerciasis disease are well known.However, unttl recently the suffering caused by skin lesions, due to onchocerciasis, and the attendantintolerable Itching had been under esttmated. It is asserted today that onchodermite refresents a heavy 2burden and that its manifestations bring about serious psychological repercussions, not only on patients, but also on their families and communities. In addition, the itching is the most painful effect of the onchodermite. [n some communities, however, 80% of the population suffers from this affectron. In Africa, the onchocerciasis vectors that are known are Similium species complexes (S.danutosunt complex, S. neavei group, and the S. albivirgulotum group). In the peculiar case of Central and East Africa, the following could be noted: The vectors of the S. damnosurtt complex have tendency of confining themselves to areas that are surrounded by either non-anthropophilous black fly populations, or in ecosystems that don't suit them. The species, therefore become "stationary". As they generally reproduce in big watercourses, their breeding sites are relatrvely accessible for larviciding. Punctual operations of vector control could, therefore, be carried out in these foci, with a good cost- effectrve ratio. ln several foci, the vector found is the S. neavei, the species that require the presence of fresh water crabs, which the pre-imago stages use as support. Because of this, the §. neavei population does not generally attain the high densities that characterize the S. damnosum. In addition, the bibliographic data indicate that this group of species has problems in reconstituting its populations when they are greatly reduced. Until 1987, onchocerciasis control in West Africa was solely based on vector control. The latter continues to be the mainstay of control, but with the advent of ivermectin, there is a new tool that has radically changed the control strategies. The latter are mostly determined on the one hand, by the geographical location of pathologies, and on the other, by the existence, efficacy and cost of intervention tools, which are as follows: lvermectin, which is a microfilaricide, administered orally to man; Vector control: thanks to insecticide spraying, this method enables the transmission sequence to be broken, by destroying the vector at the most vulnerable stage, i.e. the larva stage. The frequency of treatment depends on the duration of development of the pre-imago stages, and especrally the time that separates the hatching of larvae from their nymph stage. In the OCP area, the control of the disease was essentially based on vector control. In APOC zone, this strategy often proves to be technically impossible or less profitable. It is for this reason that the main method used by APOC is the communrÿ-based distnbution of ivermectin. However, in some rsolated foci, it has been decided to undertake vector elimination. ln West Africa, there are no cases of onchocerciasis vector elimination, for the black flies of the S. dmnosunt complex move over long distances. On the contrary, in East Africa, the use of ground treatment of larvae breeding sites has enabled the elimination of vectors in six small foci, found in Kenya (Mc Mahon et al, 1958), in the Democratic Republic of Congo (Walsh, 1990), and in Uganda (Prentice, 1974). This success indicates that a vector elimination operation could be undertaken in any focus that has similar characteristics as these six foci. Expenence has shown that smaller-scale operations, which don't conveniently cover the entrre focus, may, nevertheless have palpable effects on the S. neavei vectors, if they are continued over several months or if they are carried out intermittently over 6 to 8-month cycles. In these S. neavei foci, eliminatron is the solutton to the onchocerciasis problem. The latter is so advantageous that: Risks of resrstance and environmental degradation are low; Costs of insecticides are reduced, since control is rntermittent 'fhc fact of regularly ustng insecticides is a potential nsk factor to the aquatic environment. [n vtew of thrs rrsk, a lot of attention needs to be paid to the surveillance protocol of the aquatic environment, and to the choice of larvrcide. This choice is linked to the product (cost-effective ratro, toxrcity for non-target fauna, formulation characteristics), to the watercourse (hydrologrcal pattem, 3characteristics of breeding site), and to the black fly population present (level of sensitiüÿ to the recommended product). Whichever insecticide used, the concentraiions must be imperatively have a100% lethal effect on the black fly larvae population, through the insecticide, and aiegligible and/or zero effect on non-target fauna. with respect to ground treatment, various works have shown very good performances ofTemephos, with an active matter of 20%o emulsifiable concentrate. It is an organophosphorous biodegradable compound, with no toxic effects on mammals and fish. Its impact Ànîon-tu.get faunais moderate. In addition, OCP experience helps to know that the Bacillus tlruringiensis I{14 (Bt) could equally be used. This product is a biological insecticide. It is to be noted that an error of appreciation in the quantity of insecticide to be sprayed may have multiple repercussions on a vector control programme. In the event of overdose, the srirplus insecticide consumption has senous financial and/or ecological consequences, if the chemical u.àd i, expensive or relatively toxic. on the contrary, overdose may, on the one hand, favour the apfearance of resistantblack fly populations, and on the other hand, cause an increase in biting.ates, anàïen"" un increase intransmission. That is why a hydro biological surveillance netrvork ,nrri b" pri i1 place at thebeginning of the Programme on all the treated rivers. The impacts of the insecticide teatment on the vector populations and parasite transmission are appraised through entomological evaluation. The latter starts prior to control operations, through a complete inventory of larvae breeding sites, and the collection àf b"." data on thl identity of spiiesof the complex, the rate of bites and transmission potentials. During the operations, entomological surveillance makes it possible to detect a sizeable local production if blact flies, àL" ,o trearment Iapses or to resistance, and to detect an exogenous input of vectors. Treatment maÿ, then, be reduced or stopped in the regions where there are no black flies. By enabling the verification of the efficacy oftreatment at the pre-imago (prospecting of rivers) and imago stages (capture, identification, disseciion of females), entomological evaluation constitutes the mainslay oith" cont ol operations. Data collected during the entomological evaluation allows for the establishment of entomological indices of transmission, which are the Annual Biting Rates (ABR), and the Annual TransmissionPotential (ATP). They quantify black fly aggression and parasite transmission respectively for a subject placed at a given point, because it is representative of the most dangerous situation thatprevatls in the region. The ABR and ATP are good comparative indicators àr tn. entomological situation. They usually constitute the basis of evaluation of thà vector control results. 43. FOCI SELECTION CRTTERIA Vector elimination can only be undertaken in a focus that has a number of criteria The focus must be isolated (not at the mercy of re-invasion by exogenous black flies). The vector must be identified in order to adapt control to the species. The vector elimination activity must be easy to manage, and must guarantee a quick investment turnover for an increase in productiviÿ, and a reduction, in the long term, in the need for CDTI. 4. PANORAMA OF SITUATION IN FOCI 4.1. TUKUYU FOCUS The bibliographic data on onchocerciasis in the Tukuyu focus are relatively abundant: FISHER (1932), HAWKING (1940), Anonymous (1976, 1977), LE BERRE (tgzg), wALSH et al(1981), PEDERSON and MAEGGA (1985), V/ALSH et al (1985), PEDERSON and LOLSTROp (1986), MAEGGA (1992), MAEGGA and CUPP (1993, 1994), WALSH and MAEGGA (1996). The authors especially dwelt on the entomological, epidemiological, cytotaxonomic components, and vector control, using insecticides. These different works help to characterize this focus. 4.1.1. Presentation of focus The focus of Tukuyu (fig 1), located at the frontier between Tanzania and Malawi, spans an area of about 3,000 sq km. The region under review is found between 905 - 9045 of West longitude and 33020 - 34024 of West latitude. It extends from Lake Nyasa (south) to the Volcanic Mountains in the north and has to do with two districts (Runge, Kyela), two administrative regions (Mbeya region, Iringa region). The focus, thus demarcated, was declared isolated, since it is surrounded by natural barriers, namely Lake Nyasa and the surrounding mountains (Livingstone, Rungwe, Umalila, Undali, Mporoto). The climate rn the region is characterized by a dry season (June-October), and a rainy season(November - May). However, rainfall is all year round, with the peak in March, April and May (fig. 2, 3, 4). Rainfall figures in some areas are regularly around 2,000 mm per annum (fig. 5). The weather is relatively cold at the summit of the mountains (average 60C). On the other hand, in the plains, the weather is hot and humid all year round. This situation is due to the mountains, which annuls the influence of seasonal winds. The focus of Tukuyu is watered by three river basins, whose main watercourses are the Kiwira, the Mbaka and the Lufilyo. They take their source at a high altitude (2,400 - 2, 800 m) on Mount Rungwe. Then they descend to the plains, flowing over the slopes of the mountain, creating of rapids and favourable conditions (especrally in the dry season) for the installation of pre-imago stages of S. damnosum s.l. On their way, the Kiwira and the Lufilyo receive some tnbutaries (Luswisr, Mwalisi, Rumakali) from other mountains (Mporoto, Undali, Kipengere, Livingstone). Songwe, located in the west, and outside the focus, is a watercourse on the frontrer rvrth Malawi. Vegetation varies from savanna to dense forest and degraded forest. The latter covers the largest part of the Tukuyu focus, with Savanna and dense forests covering the slopes of the mountains. Thc populatton of the zone under study is broken into the drstncts of Kyela and Rungu,e, whrch have thc hrghest human population figure in the focus (about 69 rnhabitants/sq km). The ma;ority of inhabitants are engaged in intensive agriculture, which rs undertaken on fertile volcanic soil. The forest has, partly, been cleared for agro-industrial plantations (tea, coffee, cocoa, banana. 5rice, cane sugar), and for market garden produce and fruit (tomatoes, mangoes, pears, oranges). Fishing is undertaken along the watercourse and on Lake Nyasa by some of the ùhabitants. The identification works of PDERSON and MAEGGA (1985) and of MAEGGA and CUpp(1993, 1994) indicate that the black flies that are responsible for transmission in the focus of Tukuyu belong to the S- damnosum complex. It is, specifically, the S. damnosum, Kiwira ÿpe. The other blackflies found in the area are the S. nyasalandicum and S. bovis. Thc highest onchocerciasis prevalence rate (62.8%) was recorded at Kilugu, a village located at an altitude of 760 m on the Lufilyo. The human settlements upstream or downstreu* àf Kuluguhave much lower prevalence rates (20 to 5l%). In the entire zone, skin lesions are severe, and constitute the real onchocerciasis problem. With respect to prevalence, the area has been covered by the of rvcrmectin distribution programme, since July 1994. 4.1.2. Nature of works Several ad hoc surveys were carried out in during lg76-tgg7the Tukuyu focus prior to the start-up of APOC activities. The summary of them indicates that they dwelt on the followin!: - The determination and distribution of levels of endemicity; - The location Simulium breeding sites; - The identification of vectors; - The dynamics of pre-imago populations; - The dynamics of adult populations; - The behaviour of adult populations (namely, the rate of aggressiveness) - The vector characteristics of females of the S. damnosum (rate of parnr.ition, infestation ofblack flies, transmission of onchocerciasis) ; - The determination of the duration of larvae life; - The feasibiliry of vector elimination activities. The protocol approved by APOC in 1996 also made provision for the follorving: - The location of main breeding sites, namely those found at a high altitude; - The collection of larvae of the §. danmosums./. in the Carnoy on an positive breeding site; - The capture and dissection of black flies coming from pre-selection points (Lufilyo crater on the Lufilyo river, Lwanga Masoko on lower Krwiri, Tapio Bridge on the lower Lufilyo, and Kambasegela on the Mbaka); - The collection of rainfall and hydrological data; - Training of personnel. Finally, for the elimination of the oncho vector in the Tukuyu focus, the spraying of Temephos, as an anti-black fly larvicide, was recommended. Before any operation, u ir*"/will have to be conducted to: - Determine the actual impact of Temephos; - Measure the sensibilrÿ of the larvae of the ^s. damnosurtt s./. to Temephos; - Train local personnel on the management of nver trials and sensibility tesis 4.1.3. Results obtained The presentation of outcomes takes account of the data collection period, erther before or after thebegrnning of APoc activities rn rhe focus. This distinctron should enable: - The apprarsal of elements that allowed APOC to engage in vector elimination activrtres rnTukuyu; - stocktaking of the progress made in vector elimination in the focus. I; t Ii I 6 4.1.3.1. Data collected prior to APOC a) Prospccting breeding sites ln the 1970s and 80s, the pre-imago stages of the S. damnosuttt s./. were harvest in the dry and wet seasons on the Kiwira, Mbaka and Lufilyo rivers (Le Berre, 1970; Guillet, lggl; WalshLt al, r98r, l98s). The works of Pederson and Maegga (1985), then Walsh and Maegga (1996) confirm that thelarvae breeding sites of the S. damnosutn s.l. exist in the Tukuyu focus. fn tnè dry and rainy season, the three main rivers (Kiwira, Mbaka, Lufilyo) and some tributaries shelter pre-imago stages of the S. donurosurtt s./. The production of black flies is, nevertheless, the most important in ilw water periods, and on breeding sites at mid-altitudes (600-700m). Dispersron is important in the rainy season. On the contrary, in the dry season, the productive breeding sites are located on the middle tou..", of major rivers. ln addition to the latter, the Songwe River and its tributary (the Mwati), shelter some pre-imago stages of the S. damnosum s./. during the dry season. The same goes for the Lumbira River, whoielower course is an important source of black flies (§. damnosum s./., especially), due to the high number of breeding sites. The cytotaxonomic identification (Maegga, 1992;Maegga and CUPp, 1993, 1994) indicateD that the S. damnosum species, which lays its eggs in the main three rivers of the Tukuyu focus is the s. danutosum, the Kiwira ÿpe.kr actual fact, out of the 970 identified larvae, 910 (about 94%) were of the S. damnosum, Kiwira type. Besides, 509 larvae from the hatching of eggs laid by 7'0 gorged females on captors, were all identified as being of the Kiwira spe. Thrs vectàiis different fràrnite other ÿpes of the .S. datnnosum found in the neighbouring foci. b) Captures-dissection-transmission. Between 1979 and 1981, adult captures for determining the activity cycle of the S. damnosttnt s./., and for specifying the vector characteristics, were carried out on 9 sites, spread over the Tukuyu focus. In each of these points, two consecutive days of capture took place every two weeks, i.e. 4 days per month. The capture was spread over the whole day. Dissection of these flies and the search for O. volvulus helps to determine that onchocerciasis transmission was mainly a dry season transmission(low-water period), due to the high density of biting females, and to their beit contact with human populations. This was partrcularly high near villages of high prevalence. The rainfall figure-temperature-biting rate correlation was confirmed in a study conducted in 1987 and 1988 on four of the nine previous sites. It indicates that the ABRs were low, and did not go beyond 20,000, except on the middle course of the Lufilyo. The highest black fly densities in the dny season were obtained at between 500 and 800 m altitrude. The rates of parturition were low (22%o), and ATP was generally lower than 1,000. On the conhary, the rate of infective parous females *ui nign(38.3%). Pederson and Maegga (1985), after examrning a population of 19,500 of the S. damnosum, Kiwira §pe, confirmed that the annual biting rate fluctuated between 2,000 and 23,800. The dissection of 13,200 females (68% of capture) enabled 7.6%o of infected ones, 1.5%o of infecttve ones, and an ATP fluctuating between 0 and 1120 to be recorded. The latter rate was observed in an area, where the average prevalence of carriers of microfilaria was 54.60/0. At the end of this study, the authors confirmed that transmisslon was a dry season phenomenon. c) Larvicide treatment Bascd on cxperiences from the Kenyan and Ugandan foci, Walsh, in 1990 indicated that it was technrcally possible, ustng tnsectrcide treatment, to elimrnate the vectors (5. damnosunt s.l. and.S. treavei), from the onchocerciasis foci of Tanzania. The cost of such operations would, to a large extent, depcnd on the nature of thc tcrratn and on thc srze ol the larvae breeding sites of each focus. a 7Given the very'' gôod performances of the Temephos, with an active matter of 20oÂemulsifiable concentrate, it was recommended for ground treatment in the Tukuyu focus. Thisinsecticide was successfully used in several foci (eipecially Sogohi in uguna"J, but was neverexperimentcd in Tukuyu. However, Guillet (1981) indicateditrut À. sensibil"§ orirr" larvae in thisfocus was normal. In addition, the duration of pre-imago laboratory developm-ent (egg - adult) was190.5-210c, (three weeks), with two weeks being for the duration of larvae tire. on Àe contrary, the various field tests for determining the duration separating egg laying from adult hatching were notpositive. The operational efficacy of Temephos in the Tukuyu focus was estimated, taking into accountthe expenence acquired with oCP (Walsh, 1985; wash Ét al, l98l; Kurtak, lgsoy, and the results obtained in westem uganda (Garms et al, 1986). Thus, under the hydrological conditions of Tukuyu, it was established that the doses to be sprayed would be 0.33 I and 0.4 l/m3 lespectively ior output higher and lower than l0 m3/s. With respect to the period of treatment, the analysis of annual distribution of black flydensities enabled Pederson and Maegga (1985) to decide thai the dry season 11r". io November) wasthe period when access to the breeding sites is easiest. Besides, the flow rate of watercourses isregularly low and gradual, a larvae breeding sites are confined to some places of the watercourse. Forthese reasons, it was decided that insecticide teatments would take place in the dry season. Eachbreeding site would be teated every two weeks, and in principle,8 trlatmenf "y"t.. .p."ad over 16weeks, should be enough for eliminating the vector. As fàr the spraying points, u a.tuitéa prospecting of the main rivers and their tributaries enabled a selection of 26 oithem. - d) Prevalence The first report on onchocerciasis in Tanzaniahad to do with the Tukuyu focus (Fishe r, 1932).Hawkig (1940) confirms the presence of onchocerciasis in the focus. The distribution of this disease was, therefore, established gradually (woodruff, 1965, wHo 1966; wegesa, 1970). ln 1995, wHo estimated the number of people affected to be 650,000, but the exact extent of the endemic disease remained to be determined through investigations. Granback (1913) determined that640 of the 260 people that were examined in the village ofLufilyo were carriers of the o. Volvulus microfilaria. pedè.son and Kolstrop (r9g6j examined 2,349people aged between I and above. This sample, coming from 2l villages,i.'r.al.â that the highestprevalence rate of 62.8%o was recorde d at 7 60 m altitude ln the village oifritrgu. rn. iutt". is located on the middle course of the Lufilyo. In the other 20 villages, prevalence fluctuated between 20T and5l%' Dermatological affections constitute-the. most criticai problem, for even lorv parasitic loads cause lesions in some patients. And yet Mwaiko et al (1990) estimated that about 120,000 people were affected by onchocerciasis in the focus. Ivermectin distribution started in 1994, and until 1998, 20,000, 25,000, 40,000 and 42,000persons had benefited from treatment. d) Isolation of the Tukuyu focus The geographical siting of the focus, surrounded by natural barriers (Lake Nyasa, mountains), naturally led to the idea that the focus was isolated. This peculiar sihration, if verified, would make vector elimination feasible. In 1981, following a series of prospecting, includrng that of rivers Lunrbila and Songrvc.Gurllct concluded that the focus was not as rsolated as thc geographical environment made it look.Conseqrrently, vector elimination became hypothetical Cytotaxonomic studies (Maegga, 1992; Maegga and CUpp, 1993 and 1994) waived thedoubts of Guillet (1981) as to the isolatton of the Tukuÿ, fo.ur. In effect, apart from the s. dtnrto.strttt, 3 8Kiwira t)Pe, no other cytoÿpe could immigrate into the focus. In other words, from the cytotaxonomic point of view, this was an isolated focus, which only contains the S. damnos;u,n, Kiwira ÿpe species. The extent of isolation is, however, very high, otherwise only one ÿpe would not be so predominant in the area. It is therefore, on the basis of these works, the entomological studies (pederson and Maegga, 1985) and epidemiological studies (Pederson and Kolstrop, 1986) that the Tuduyu focus was dectààd isolated. Vector elimination of the said focus could be undertaken with success (Walsh and Maegga, 1996). 4.1.3.2. Data collected after the start-up of APoc activities a) Prospecting breeding sites This was mostly done by the national team. Between October and December 1998, the productiviry of breeding sites of the main rivers(Kiwira, Mbaka, Lufilyo) was regularly monitored. This study aimed at determining the upper limit(altitude) of the distribution of pre-imago stages (fig.6).Thus,31 breeding sites were geo-rllerenced and prospected for harvesting pre-imago stages in the regions of Mbeya (Rungwe, §ela, lleye,Mbarali), lringa (Ludewa) and Rukwa (Sumbawanga, Mbeya). Out of l8 positive breeding sites, only 9 shelter the S. damnosum s.l. In the districts of Rungwe and Kyela, only a breeding site was found tô be positive, out ofthe 17 prospected. In September-October of 1999, the S. damnosurn s.l. was found in the entire breeding sites(13) on the main rivers (10 breeding sites), and on some tributaries (3 breeding sites). Therà was, however, some dispariÿ between the plethoric imago population and the scarcity of pre-imago population in the breeding sites. In 1999, 24 breeding sites were prospected and 14 were found to shelter larvae and/or nymphs of the S. damnosum s./. All the positive breeding sites were geo-referenced, and larvae were sampled in the Camoy. This activity continued in February 2000 when two breeding sites were found to be positive, out of the 11 prospected. Between July and September 2000, the prospecting undertaken by Barro, apart from the pre- established limits (Walsh and Maegga,1996), made it possible to visit 28 breeding sites, l3 of which were positive on the main watercourses (Kiwira, Mbaka, Lufilyo). In addition, out of the 2l breeding sites prospected on the tributaries, 9 sheltered pre-imago stages of the S. danmosum s.l. From the altitude point of view, the distribution of the S. damnosutn s.1., was between 412 m and 1,000 m approximately. This distribution was variable, depending on the river basins. b) Captures-Dissection-Transmission These activities were carried out by the national team. The analysis of capture and dissection sheets indicate that the captors did not generally apply the usual standards for capturing black flies(Barro, 2001). The following results are therefore to be considered with caution. Between October and December 1998, a day of capture per month, was undertaken at Tapio and Kambasegela, as against two days at Luhlyo-crater and Lwangwa-Masako. These capture points tally with the various levels of prevalence in the area that is under treatment with ivermectin. Thus, 225 females were captured and dissected. These dissections enabled the recording of 99 parous females (44%),19 infected (19%) and 7 infective females (7%). Between January and December 1999, tables 1,2,3 and 4 indicate that 144 days of capture enablcd a harvest of 1,362 females at Lufilyo-Crater (499 females), Lwangwa-Masako (635), Tàpio- Brrdge (149) and Kambasegela (79). The dissection of 1357 females revealed 390 parous femàles(28.7%),40 infected (10.2%) and 3 infectlve ones (0.76%). The ATP was 83, for MTp was 23 in June, 60 in August and zero for the other ten months. The average black fly density was 9 bites/man/day, but e t -v 9 taking into account a distribution per capture point, it was 3, 13 and 6 at Kambasegela, Lufi lyo-Crater,Lwangwo-Masako and Tapio-Bridge respectively. The entomological evaluation undertaken between January and December 2000 (tables 5,6,7 and 8) indicate than in 144 days, 6240 females were captured at Lwangwa-Masako ( I 815), Taplo n.iage(1893), Kambasegela (300), and Lufilyo-crater (2230). out of these females, szjo were dissected, ofwhrch 176l were parous (30.5%), 144 infected (8%), and l8 infective (lyo). The MBR flu*uatedbetween 8 and 3930,465 and 3810,30 and 1695, and between 98 and 3068 àt Lwangwa-Masako, Tapio-Bridge, Kamasegela and Lyfilyo-crater respectively. For these same capture points, the MTp was nil forsix months of the year: January, February, March, April, May and November. In 2001, 9923 females were captured in the Tukuyu focus (fig. 7). The average densiÿ was 4gbites/man/day. Besides, females were more abundant on the Lufilyo (66 bites/maiday;, then on theKiwira (38 bites/man/day), and finally on the Mbaka (14 bites/mar/day). For these same watercourses, the MBR fluctuated between 430 and 5880, between 38 and 4073 andbetween l5 and 2550 respectively.Data on dissection are not available. c) Larvicide treatment The sensibiliÿ tests, river trials and the first ground treatment of the focus were entirely carriedout by the OCP team under Mr. Barro. It is worth noting that the national team took part in these operations- An APOC employee also participated in this first ground treatment operation. The sensibiliÿ tests that were carried out in October 1999 indicate that the larvae were subjectedto a series of concentations: 0.00975 mÿL0.039 mg/I,0.156 mg/l, 0.3125/1,0.625 mg/|,1.25 mÿl and2-5 mgfl- At a temperature of 2O-22o.C, mortaliÿ rates of 5O%, gO% and 100% weîe recorded, with concentrations of 0. I 56 mg/I, 0.3 125 mÿl and 0.626 mgll and above respectively. These results indrcatethat the sensitivity of the larvae to Temephos is excelleÀt. In effect, the CL 95 oi the low mortaliÿ (onlydead larvae) is up to 0.66 mg/I. Two river trials of the Temephos were conducted in 1999 on the Mbaka and the Lufilyo. Forthis latter watercourse, the section chosen was about 15 km long. This stretch was treated at a dose of0'41/m3 i.e. a concentration of 0.33 mg/I. Due to the probleÀ of inaccessibility, no evaluation was carried out before and after treatment beyond the Lufiiyo-Rumakali confluence. As for the results obtained on the Mbaka, they indicate a good carrying capacity of Temephos. In effect, for a floiv of 4.3 m3/s and a dose of 0.1 mÿI, the effective carrying capaciry (100% oiuncoupling; *as 7,060 km. Itmust be noted that the clear nature of the river water (turbidiÿ lower or "quà'i to 5JTU), and itstemperature ( 18- 190C) contributed to lessen the effect of the Temephos. The latter first of all settles onthe .p-articles in suspension (need for a high turbidity rate), which are then injected by the larvae.Besides, any temperature lower than 2l.c becomes u ii*iting factor for toxiciÿ of organophosphorous compounds (particularly Temephos). Between July and September 2000, two sensibility tests were conducted on the Kirvira andLufilyo rivers. with a CL95 of 0.384 mg/l for a high mortaliÿ rate, the results indicate a good sensibiliry to Temephos on these two watercourses. A mortality rate of 100% is observed at 0.625 mg/I,but some moribund_subsist at doses of 0.625 mgand I.25 mg/I. The river tests of the Bt H14 Tecknar on river Mabaka show that at the normal dose of 0.72 mgllby m3/s and a flow of 2.5 m3/s, only 4l .3%o ofdetachment of older larvae at 4.5 km from the point ofspraylng were recorded. The maximal effective carrying capacity-observed is about I km. Besides, onRiver Lufilyo, at a dose of 0.54 I per m3/s, and a flow o1s,sso m'/s, the nlo.tuiiÇ orold Iarvae rs only16.2%. The efficacy of Tecknar was almost zero at 6 km. The first ground treatment campaign meant to eliminate the S. damnosum s.l. of the Tukuy,r:focus through Temephos spraying, tookplace from December 200lto February 2002, The three basinsof the focus (Krwira, Mbaka, Lufilyo) were submitted to weekly treatment with remephos for six weeks,at a dose of l'33 mg/l. Each week, the insectrcide *u. .p.uy.d at 53pornt, and a total of ggl lrters of v- 10 Temephos was used for the entire campaign (fig. 8,9). The results indicate that prior to treatment, 35breeding sites prospected sheltered all the pre-imago stages of the S. damnosum ..i. Aft". the first week of treatment, no breeding site visited on the main rivers was found to be positive (fig. 10, l l, l2). On the contrary, two positive breeding sites were found on the tributaries (on the «asyaÙÀa and a triÉutary ofthe Mbaka (Mb300). The total absence of nymphs indicates, however, the excellent efficacy oith"Temephos. d) Isolation of the focus The data acquired after the works of Walsh and Maegga (1996) indicate that the Songwe River, a natural frontier between Tanzania and Malawi in the downstream section, shelters the S. damnoru... l. (NOTF, 2000). Besides, tributaries of this watercourse take their source from the territory of the focus, mainly along the Mwalisi. The latter is the main tributary of the Kirwrra River. It flows into the section that shelters the S- damnosum s.l. (Barro,200l). In addrtion, a number of tributaries of the Songwe may, from this nver, constitute the contamination corridor of the Mwalisi River. Finally, the Son[we and Kiwira rivers are close to each other, near the border post at Lake Nyasa. It is also worth noting that in the South Eastem part of the focus, some Km from Lumbira, is theKilondi River. It is big, perennial and may also shelter the S. damnosum s.l. Since this river and theSongwe River are located outside the Tukuyu focus, could the latter be isolated? 4.1.4. CDTI status in the Tukuyu focus The CDTI project in the Tukuyu focus within I year. The data collected between May 2000 andApril200l may be summed up as follows: ' The population of the Tukuyu focus is broken down into 46 villages, 38 of which are in the Rungwe distnct, and 8 in that of Kyela. These districts are located in the meso and hyper- endemic onchocercal areas. ' In November 2000,261 boxes of mectizan, representing 130,500 3 mg tablets were supplied to the NOTFs. For activiÿ implementation, 82,635 US dollars (of which 47 dollars was transferred to the NOTF) was put in place by APOC. This funding was used to procure material and to cover expenses relating to fieldwork. 87 to 100% of the training objectives for technrcal personnel involved in the CDTI were attained. The inhabitants around the Tukuyu focus are estimated to be 84,310 persons, 65,2ll of whom were treated with 123,000 ivermectin tablets. The rate of coverage is 66%o. Non-eligible persons (children below 5 years, expectant women, patients), and absentees represent l7o and 9.7%o respectively. This means that the coverage rate of 660 îs excellent, since the number of people who refuse treatment represent only 0.3%. In conclusion, it could be said that CDTI is going on satisfactorily in the Tukuyu focus. The arrangements made (namely undertaking treatment in the dry season, providing financing, and acquiring tvermectin in time) should contribute to improving the therapeutic coverage rate of the next CDTI campaigns. 4.1.5. Budget for vector elimination activities For thc stafl-up and conttnuatton of eltmrnation activrties. AIIOC provrded regular financral asslstance on the basts of letters of agreement (contracts). Thc table belorv suuts up the budget component of the project. I I a11 Period covered Cash transferred to ficld Amount spent US$ Purchase equipment o Total cost Oct 99 25,01 I I1,880 100 35 Oct.99-S 00 50,717 32,518 92,455 124 973 Oct. 00-Scpt 0l 43,199 29,216 8,000 37 216 Oct. 01-Scpt 02 48,983 NA t7 940 t7 940 Total t67,gl0 73,614 206,750 290,364 4.1.6. Discussions - Remarks Given thc various results presented above, it appears that prior to the start-up of the activities ofAPOC, several pieces of technical information were available, due to regula6u*.ÿ. carried out in theTukuyu focus. This data helped to select the focus for vector eliminatiàn activitie;- However, before starting control, APOC assistance helped to cristalise some points. These included mainly: choice ofcapture points, determination of the duration of larvae life on the field, determination of vector characteristics on the entire focus, the sampling and distribution of all blaci< fly species found in thefocus' the determination of insecticide spraying points, the effective carrying "upu"ity of the fe*ephosand the sensibility of larvae to the chemical on the main rivers and tributariei, una nütty tte t ainirg àipersonnel on all aspects (technical, practical) of entomological evaluation. These results are analyzed inthe paragraphs on the distribution of the S. damnosurn s./. in the focus, isolated from the focus, vector control and entomological evaluation. a) Distribution of S. damnosum Vector elimination is the result of total efficacy of larviciding of all vector breedrng sites, which had been recorded over a sufficiently long period. But the spraying points meant to cover the entirebreeding sites went from 26 (Walsh and Maegga, 1996) to sf (earro, z}oz), Thus, follorvingprospection, it appears that the main tributaries of the Kiwira and the Mbaka a.e almost all colonized bÿthe S. donutosum s.l- [n addition, the small streams, which enter the watercourses (main rirers anâtributaries), rvhose stretches shelter the S. damnosum s.1., are also colonized by their embouchures. The resultsof theprospectingcarriedoutin 1998, 1999,2000and2001 indicatedti,attneaistibutionof theS' dantnosurn s./. in the Tukuyu focus is more important and more extensive than the limits mentioned inthe Walsh and Maegga report (1996). The onchocerciasis vector is found both upstream anddownstream of the said limits. Besides, given the great number of secondary tributaries, it is probable that some flow during a part of the year (even all year round), hence the pâssibility of breeding sites sheltering the S. damnosum s.l. (Barro, 2002). This means the current distribution of the S. damnosum in the Tukuyu focus, is perhaps notdefinitely established. However, it is of utmost importance to identiÿ the S. daÂnosum s.l. found on the various watercourses. In effect, Maegga (2001) notes that for the pu.t tt.."l*.., tto larvae harvested have not undergone any cytotaxonomic identification. And yet, some bieeding sites (for instance Mwahsi on the Mbaka) shelter several pre-imago stages, rvhereas the number of bies/man/day remainslow. This contradictory status poses a problem of the identity of species, rvhich are so anthropophilous. Bcstdes, thc identification will have to do with the tnbutaries (namely Rivers Mrvati and Mtumbrviz), River Songwe in Tanzania and in Malawi. For the latter, Maegga (2001) proposes that a joint missiop of Tanzanian and Malawi entomologtsts should prospect the Chipita and Misuka mountains in the northernprovincc of Malawi, which is adjacent to thc Bundah and Umalrla rnountarns of the Tanzanian drst'ct oI lle1e. b) Isolation ol thc focus -l'he hrst condition requrred for unde(aklng vcclor clrmrnatiol rn a focus rs that rt must bc rsolatcd. [n thc case of the l-ukrryu focus, the essentral geographical criterra (presence of naturalbarrrcrs), arrd cytotaxottomic rdcntrfication of tltc vcctor antl rts urlrqucncss to thc focus (S_ 4ttttttt.-st,tt. 88,3 55 T2 Kiwira ÿpe), made some authors (Walsh and Maegga,1996; Le Berre, 1970) conclude that the saidfocus was isolated. On the contrary, other works (Guillet, 1981; NOTFs,2000i Barro,2000 and 2002) reported the presence of the S. damnosum s.l. in the middle course of the Songwe Riu"r, which is a natural frontier between Tanzania and Malawi. Besides, the numerous small tributaries of the Songwe,during the period of flow, could be sources of replenishing of the S. damnosurz s./. Of course all thesé watercourses are found outside the Tukuyu focus, but the flying ability of the S. Damnosum s./. is such that it can get to any breeding site of the focus. It must be noted that iome watercourses are so close tothe focus that simple dispersion would be sufficient. These last results call for another entomological evaluation of the Songwe basin, located on the western side of the focus in Tanzania, but also in Malawi. The same might go for the Kilondo River, located in the southem part of the focus. This river i. Uig,perennial and could shelter the S. damnosum s.l. Meanwhile, there are doubts as to whether the Tukufr-r focus could be called an isolated focus. c) Vector control The sensibility tests conducted in 1999 and 2000 by the OCP team (Bano) underpins the observations made in previous works (Guillet, 1981; Walsh et al, l98l; Garms et àt, t936y, and confirm the very good performances of Temephos with an active matter of 20%o emulsifiable concentrate. Not only did the river tests help to solve the problem of carrying capaciÿ of the Temephos, but it also showed the superiority of its performances, as compared to those of the Bt H14 Tecknar. Thus, the first vector elimination campaign proved to be efficacious, for after only a week of treatment, no positive breeding site was found on the main rivers. Additionally, the total absence of nymphs also shows the efficacy of Temephos on the breeding sites around the tributaries. This chemical rémains the selected insecticide for conkolling the S. damnosum s./. in the Tukuyu focus. For each series of spraying, there is still a problem relating to treatment cycles, accessibility to spraying points, and the dttermination of insecticide quantities to spray (especially in the_absence of a spate gauge). Treatments was weekly, this time lapse between two teatment sessions sufficiently covers the duration of larvae life, which in view of the water temperature (180C-190C), is at least two weeks. d) Entomological evaluation The entomological evaluation is the tool for appraising the results of insecticide treatment on the vector population and parasite transmission. The data collected, though has information that may differ from a document to another, may be characterized by some traits as follows: the captures have great variation in the number of females harvest from one year to another. Thus, for the same capture point, the same month (practically the same conditions), and the same number of days of capture, the MBR recorded in 2000 at Tapio-Bridge is 3 to 607 times higher than that observed in 1999 at the same capture point. The same goes for Kambasegela, Lufilyo crater and Lwangwa-Masako. It is generally agreed that, apart from the periods of re-invasion, when the black fly densiÿ lowers, the physiological age increases, and üce versa. The results obtained àt Tukuyu do not tally with this rule. The dissected black fly population seems, in all periods, to be made up of young females. It must be noted that this part of the population is usually captured in the first hours of the morning (7.00 a.m.-9.00 a.m), or in the last hours of the aftemoon (1600-1800). No infective female was captured in 1999 at Kambasegela, Lufilyo-Crater and Tapio. And yet 527 parous females were dissected, of which 55 were infected. Even at Lwangwa-Masako, only 3 infective females were recorded. Certainly, the MTP is nil for some months of 2000, but each of the ATp obtained at the different capture points is high (minimum ATp=l12 at Lwangwa-Masako; maximum ATP:282 at Tapio Bridge), wtth a tolerable limit (threshold) of 100 Lilmarÿyear in the savanna zone of West Afnca. â , et3 4. 1.7. Conclusions-suggestions Thc "vector elimination project" in Tukuyu now has weak point, which must bc underscored inordcr to make control activities more effective. For the attainment of the s"t ot,,""iire, r,ue would likc tolist sornc elements on which it would be necessary to dwcll. - vector elimination requires total efficacy of larvicidrng, which is undcrtaken on all brccdingsitcs' Given the topography of the terrain in the Tuku-yu focus, it is of absolute necessity tocontinue with prospecting, especially in periods of low water when thc carrying capacity ofTemephos is considerably reduced. - The need for larvae controls to evaluate the efficacy of larviciding, the probable increase in thenumber of watercourses to be treated, and the topography of the tîrrin'r"qure, rvith respect toscrvice quality, thc recruitment of temporary staff durrng Lach control "o*pàig,- The water levcl gauges in the focus now are generally làcated at the extrcm. Jno. (upstream anddownstream) of the watercourses. Due to this, their exploitation is difficult in the middlecourses' which prove to be the areas with the highest black fly densities. Àesides, there is nowater level gauges on the tributaries. This situation needs to t" "o..."i"a t.rouing gauges,updating of tarase graphs), in order to make for good projection of doses and quantisr oflarvicides to be sprayed. - In order to monitor the evolution of the settlement of lotiçal organisms, apart from black flies,under the effect of black fly larviciding, it i. n""".r"ry toÏui".".r"*."Lïyaro-biological data.It is therefore of utmost necessiÿ to collect the maximum of data À'n-.n,on,ofauna andichtyofauna. - some authors affirm that the Tukuyu focus is isolated. others, however, given the proximity ofthe songwe River, its tributaries and the presence of the s. dantrtosurttr.l. In .o*. *u,..courses,have reservations on this. It is thereforsnecessary to rna..tut. u.,..,to*oiogi""r re-evaluationof the basin of the Songwe in Tanzania and Malawi. In addition, and in or-der to conflrm orinfirm the assumption of a re-invasion of the treated zone by the exogenous -5.-clarrtnosuru in thefocus, it is necessary to identiÿ the vectors, with precision. - The results of insecticide treatment on the vector population, and the transmission of the parasiteare appraised, thanks to the entomological evaluation. But the current data on captures shorvsome serious disparities. It is imperative that vigorous action is taken (sensitization, supervision) in order to make these data more reliable. In actual lact, the capture and dissectionresults raise some issues: * were captures carried out according to the standards (7 a.m. - 1800), or only at certain timesof the day (namely in the morning, given the physiological age)? * Is the search forstages of o.volvulus inparàui femJes sufhciently done *,ith precision? - The implementation of the "vector elimination" project at Tukuyu .rppo... matenal means andlogistics. The latter, which are made availabie io the prolett by Apoc, are not parriallyallocated to the said project. A solution will need to be found, so that atL tne logistics madeavailable by APOC will be actually devoted to the implementation of the project. ln view of the various points above, which sum up the various difficulties that camc up during thepractical implementation on the field, the eradication oithe s. danmosurr s.l. b1, ground treatment rn theTukuyu focus, risks to be an objective that is too ambitrous. on the other hand, tlî therapeutic coveragerate (66%o) and that of persons (o-3%) who refuse treatment with ivermectin, indrcate that cDTI is gorngon sattsfactorily in tl-re Tukuyu focus. The measures taken (namely, undertakrng i.àu,-"n, rn thc dryseason, fir-rdrng financing, and procuring ivermectin in trnre) should contnbfte tà rmprovrng thethcrapeutrc co\/erage rate of each of the neit CDTI campaigns. l4 4.2. BIOKO F'OCUS The island of Bioki rs a nlass oIcarth of volcanic origin of 2,017 sq km (72 kn-r long and 35 km widc). I1 is located in the Gulf of Guinca, on the coast of Cameroon and Gabon, Ùctneen lultude, :o+giN and 30l2'N and longitudes 1207'E and 12040'E. The island is characterized by a very rugged relief, made up of mountains, some surnmrts of whrch arc partrcularly high (Basile p.rt, :Ollm; Caldcra daLuba:2661 m; Biao peak: 2009 m). The chmate of equatorial type, with rwo scasons: a dry season (November to March) and a rainy season (Apnl to Octobcr). Thc annual average temperature is 250C. Rainfallvaries from l930 mm in thtNorth to 10.990 mm rn thc South (fig. l3). The island of Bioko belongs to the tropical forest belt. About 90% of the territory is covered byforests- They are particularly dense and entirely cover the rivers, which are very difficult to access. In the upstream and downstream parts of the only main road, only paths link cocoa farms, which provide access to the rivers. The hydrographic network (fig l4) is made up of small low-output rivers, which descend from the mountains. Some watercourses don't have buffer zones (estuaries, iagoon)); They flow directly in the sea, hence the influence of the seawater on their aquatic fauna. Due to the slope, tÉe rivers flow fast(0.3 to I m/s) and the current is turbulent. They are particularly numerous (247),'but short. The average length is about 7 km (maximum: l5 km). Each watercourse shelters several breeding sites. The epidemiology of onchocerciasis recalls that of West African tropical forests (Mas et al,1995). The average prevalence is about 15% (85% in persons aged over l5). For CDTI, the targci population is estimated to be 60,000 persons. Thc Bioko island rs the only tsland knorvn, to date, to be endemic u,ith onchocerciasis. The vector is a member of the S. damnosum complex, identrhed under the name S. vahense, Bioko spe.The geographical location of the island shelters it from re-invasion. This isolation, +O km frorn ihe Cameroonian coasts, led to the thought of vector elimrnation, coupled with ivermectin distribution, which started in 1990. 4.2.1. Nature of rvorks The studies on the onchocerciasis vector on the Broko rsland started in 1989. Then a TDR study on the feasibility of vector elimination in this focus was conducted in 1996. Finally, in 1999, various complementary studies rvere carried out under the pro.;ect, financed by APOC, and entitled ..Vector ehmination of the Bioko Island". The objectives are specific to cach study, and are presented as follows: a) TDR study on feasibrlity determine the productrvrty ol larvae brecdrng sltcs ln the dry season; trace the plans of rnsecticrde lreatntent; cstablrsh thc rdentrty of vectors, tn re latron rvrth that of black flies of the rrearcst zoncs, u,rth a vrel to appraising the extcnt ol- rsolatron of tlicsc vectors; cvaluatc lhc possrbilrty of rc-ruvasron lrour thc coasts; ctlllect all usclrrl ttrlitrtnlttttltr t«r tltc rnrPlcnrcntatr()r) ol'thc "r,ct:tor clrrrrutatrr-rn" pro;ccts. lt) E,lirnirratirrg the vector fronr thc Bioko islln«l lrarn thc natronal tcaur on thc colleclron ol'tlasc cntorrrologrcal clala; coilcct entonroloqtcal basc data, t c ; 15 - establish base data relating to the impact of treatment on the environment (obtain base data onthe aquatic fauna; evaluate the impact of Temephos on the invertebrates and ichtyofauna and rivers of the island); - study the sensibility of larvae population of the S. damnosum s.l. to TcmepS.s; - study the dyramics of rivers and their tributaries; - t undertakc a first ground treatlnent campaign, and cvaluatc its impacl on thc transmissio, ofonctrocerc lasls. 4.2.2. Outcomes obtained Thc vector elimination project is the result of several years (at least l0 years) of preliminarystudies, toward dctcrmining thc feasibility of such u, op"ruiion at Bioko. The varrous results arepresented below, in items entitled: isolation of the island, prospecting, larvrciding and entomological evaluation. a) Prospecting ofbreeding sites The works carried out in April and May 1996 by wilson, indicate that 224 rivers wereprospected, i.e-91ÿo of the entire watercourses of the island. At this period,20 of the rivers prospecteà were inaccessible, 17 of which sheltered the larvae of the S. vahense, Bioko ÿpe. on the contrary, 130(58%) of the rivers showed a flow, and 45 of them (2ro%) were positive riihe pre-i-ago stages ofSimulidae, 23 (10%) of which are of the s-. damnosum s.l. The 2Ô7 prospecting 'sessions carried outenabled a breakdown of the rivers into two categories: those that shelte; the S. daîtnoru,r r.l.,and thosewhose flow was sufficient for the settlement of pre-imago stagcs of S. datrtno.srrrr s./. [t must also benoted that 21 rivers could not be prospected,12 of which rveà capable of sheltering s.dantnosttnt s.l.breeding sites. With respect to cytotaxonomic belonging, the 474 specimens examincd indicated thatthey had exclusively to do with the §. yahense. Since its ikomosome characteristics do not correspondto those oI the standard yahense, it has been baptized the s. yqhsnsc, I]ioko spe . The numerous prospecting activities undertaken rn January-February 1999 (Bano) con{irm thatthe rivers are numerous, short (i k " long in the average), with falls and rapids. Tàeir florv rates weregenerally lorv (lower than 1 mt/s;, hence the insignihcant invasion by the S. datrnosutrt s.l. Even theartihcial supports were not densely colonized in the third week. [n addition, most of the larvae were attntermedtate stages. No pre-imago stage was harvested beyond an altitude of 600 metres or in rvaters whose temperature was lower than22o5C. In March-April 1999, Meyer carried out a series of prospecting of rrvers of the Bioko Island. He concludes that most of the watercourses are protected by a luxuriant vegetatron, hence the difficulry inprospecting. The South, which accounts for about 40% oî the territory, is inaccessrble on the ground. Inthe^dry season, the flow rate of watercourses is generally betrveen 0.2and 1 m3/s. Cool water(190C<T0<260C) and clear water (turbidity generally làu,er than 5JTU), florvs on the rocs ground at an average speed of 0.5m/s (0.3m/s<speed<1m/s). The pre-rmago stages were rare, due to the fluctuationsin water level, following rntermittent rains. Prospectrng on th" Musola and the Eba (tnbutary) indicatethat betwecn 500 m and 800 m, there was no S. damnosutn s.l. Cheke et al. carried out new prospectrng rn Apnl 1999 on I I rrvcrs olthe rsland. The objectrvc was to detcrmine the maximal altitude at whrch thc S. damnosum s.l could colonize thc breeding sites.Prc-irnago stages werc harvestcd on the Trburones rrYers (North), Musola, goofo, Apu, Coo andBaloapr. 'I'he trials conducted at 345 m,554 nr antl 808 m could only cnable the collcction of S.danrtrosut.t.t Srmultdac. It is to bc noted that it u,as thc first tinrc a positrvc brcedinc srtc \\,as disco'erecl on the []ekrlltr ln Dccenlbcr 1999, prospcctrng was on solnc \\'atcrcourses rn the regron of Maluba. -l5e results lrrcscntcd by MCCall (1999) indicatc Lhat24 sttes, rncludrng 8 at altiru<lei:so-r,1gônr) rvcrc vrsited-'l-hc § damnosum s.l. (1lre-imago stages) was encouulcrcd rn fivc rrvcrs (Nalc, Baloapi, -l-oa, Bioco anda rl\/cr wrthout a namc), which do not al)l)car on tlrc lrst drau,n up by \\/rlson f iOlfr; No posrtivc 16 breeding sitc was found beyond an altitude of 600 metres, nor in the waters with temperatures below220bc' on thecontrary, in the Moca region, two biting females were caphlred at 750 and 1,250 m. Atthe timc of the investigation, the flow.ri. *u, 1.05,0.14 and 1.05 m3/s on the Apu, Biala and Malahorcspectivcly. As part of thc studies on the distribution of pre-imago breeding sites on thc island of Bioko,54rivcrs were visited at thc beginning of thc rainy s^eason llunJ-luly). Mas et al. (2000) conclude that outof thcse watercourscs, water tempcrature was 250C. [n addition, out of 52 acceÀsible rivers, g shelteredprc-rmago stagcs of the s- damnosum s.l- It is to be noted that during the samc p..ioà, a Iot of adult Sdamnosum s'l were captured during the prospection. The prospection carried out i., January-February2001 by Meyer et al., just before the beginningof larvicidinj *u. to determine access points to therivers, rivers to be treated, larviciding points und do.., to be ap"ptiea at each ur."Ji"g .ite. 39 sites wereLherclore prospectcd among which 8 were having s.datnnosum at pre-imago stages. fuater temperaturesfluctuated between 1809 and 250c. Flow rates were berween o.r to s*jlr: Tî;:;..;irl,o" *u. sprayedat 40 points, and out of the l0 breeding sites controlled after treatment, 3 were found to be positive. In February 2001, Meyer and 'wilson undertook prospecting of the southern part of the BiokoIsland, between Riaba and Luba. out of 4Orivers, they noàd ôu, *"in basins graav, üoaba, osa, ole).Each of these rivers is a series of falls and rap_ids. At the time of prospecting, the osa River was almostdry, but the other three had good flow. The flow rates were 20-j0m% r;;i-ô;ii o., tr," Moba andole respectively. These flow rates are such that the BT seems to point to the need for treatment ofbreeding sites, except that these treatments, preferably aerial, would take time due to the nature of therelief. Pre-imago stages were harvested in abundance, sometimes, on these watercourses; they usedIeaves and stems that stand out of the water as supports. As for the small tributaries, they were coveredwith vegetation, but due to the topography of the terrain, there are openings that should make aerialtreatment possible. b) Captures-dissection-transmission Right from 1992, the captures made on the Sampaca and Timbabe rivers helped to establishannual fluctuations of the MBR (fig. 15, 16). From January to April, black fly a."tiii., were generallylow (MBR<100). on the contrary, from May through December, the MBR fluctuare between 300 and4,000, and between 1,000 and 8,000 at Timbabe "Àd sr*pu"a respectively. The maximum caprure rsrecorded in October. In 1996, the dissection of 56 females enabled Wilson to observe [4 parous ones (25%) , 2 oîwhich were carriers of infecting larvae. For comparison purposes, 369 females that had been conservedin alcohol since 1993 were softened, coloured and disseàteà. rn" results indicated 42 infected females(11.4%) and 8 infective ones (2.2%) BetweenJanuaryandApril lggg,3146femalesrvereharvestedin2gdaysofcapturecarriedout by the national team at Sampaka, Barley Corn, Musola and Balada Luna ouu. Âmong the g7g femalesdissected, the physiological age fluctuated between 14.8% and 11.3oÂ. The infestation rates rvereparticularly high (infected females: 44oÂ; infecir- e females: g%). In March 2000, Mas and Tirados recorded l4Lillo0o parous females and a MTp equal to 15.Thcse results helped to extrapolate the data of Gcenen (1993), and to obtain a rraxrmum of 400 Lrl,000 Parous and a MTP of l'600. Finally, rn 1997, Mc Call and Mas observed 1,440 Lil1000 parous femalcsin thc dissection rcsulLs. C)apturcs, lbllou'ed by drssccttons, wcrc carrrcd out by the natronal tcanr ln Aprrl-May 2000 o,thc Sarnpaka (Sampaka), Apu (Barley Corn), Musola lMusola) and Ruma (Balacha ol'I{iaba) rivcrs.l'able 9 indrcatcs tltal rn 3l days, 5138 femalcs were captured, 2,890 drssectcd, of which 1,2 l5 rvcrc Parous (42%\,85 infccted (6.9%), and 25 rnfcctive (2%). The avcragc black fly density for thc pc,ocl\\/as about 166 bites/man/day (mrnimum=40, nraxrnrurn:383), hcpce th; usually high MIll{ a T7 (minimum=1305; maximum=11,475). Taking into account a distribution by point of capture, thephysiological age fluctuated between 33.5%o and 53oÂ. With respect to infestition rates, they werebctween l-6Yo and ll.5oÂ, and between 0.5% and 5o for the infected and infective parous lcnrales rcspcctivcly. Transmission was lowest in May at Balacha (MTP=ll), and highest in April at Musola(MTP:270). Thc results of thc captures carried out in February 2001 by thc national team (table I0), duringlarvictding, is as follows: 9 capture points, l7 days of capture 1i to: days per poiàty,3,293lemales captured, of which 1304 dissected. The parous fcmale percentages go from'2i..à% to 64%o, and theinfestation rates are from 5.3% to25%o (infected females), from 0 togo)o(infective females). Apart fromMoca at river Chuba (6 females, MBR = 300), the black fly densities ivere relatively high (minimunrMBII=2970; maxintum:10,380). The trials carried out at thc upstream part olthe watercourses helped to capture 632 females, of which 149,279,198 and 6 were captured at altitude 550 m, 600m, 7g0 m ànd1,250 respectively. In addition to the February results, those of the captures-dissection of the other months of the year 2001 are indispensable for appraising the impact of the first treatment campaign on onchocerciasis tansmission. These elements should be available at the project Coordinato.'s, fo, oi Zô;iNovember 2001' Dr. Mas wrote to the Director of APOC: "J.M. Mba, ento-rnology technician, is sending results of the Simulium catches and dissections, on a periodic basis, to Dr. Wilson". c) Preparations towards the lirst ground larviciding campaign At the end of prospecting conducted on all the watercourses of the Bioko Island, Wilson (1996) concluded that 1,020 km of stretches, belonging to 52 rivers, were to be subjected to larviciding. The "vector elimination at Bioko" started in January 1999. From this date to the end of July2000, the various activities are summed up as follows: In January 1999,a team of external scientists stayed at Bioko. Advantage u,as taken of their stayto train four entomologist-technicians on fieldwork (capture and dissection of Élack flies). Besides thi;,two scientists of the Spanish Cooperation underwent training at OCP, to enable them ensure effecti'e supervision of the collection of entomological data. Two insecticide tests rvere conducted in January-February 1999, and the results shorved thatlarvaeofthe.g. donmosumofBiokowereverysensitivetoTemepÈos. Ineffect,Barro(1999)notesthat with 100% of mortality at 0.3125 mg/I, the results of the insecticide tests conducted on the lanaeharvested in the Musola and Apu Rivers were excellent. These sensibilrry studies indicate that at florv rates of 0.14 m'/s, 1.05 m3/s and 1.6 m3/s, corresponded to the effective carry capacities of 650 m,25 km and 38 km respectively. In March-April 1999, works on the impact of insecticide treatment on the environment rvere carrted out tn thc Bioko focus by scientists from the Museum of Natural History rn London, and from the Water Resources Institute of Accra. These studies were aimed at collecting üase data for an impact evaluation on larviciding of the non-target fauna (namely rnvertebratcs and fishl Meyer (2000) notes that most of the rtvers may be trcated lrom thc bndges that span the main road. Thc latter is locatcd at an altitude of between 100 and 400 m, and 14 km fiom thc sea. The ri'er zonc, wlre re the pre-imago stages of the S. danurosturr arc most numerous, rvould thus, be covcred by treattrlents conductcd from the bndges. I{c also recorunrcnds that aerral prospectrng be undertaken in thc southcm parl of the island in 200 l, in order to collect information on thc acccssrbility of rivers, and theproductrvity of the rr breeding sitcs. At thc erld ol'2000, and alier scveral sclcctrun lests, srx pcrsons \\,erc trarned rn llcldrvor.k: Irarvcst and rdentificatton of larvae, nymphs and adults of the S. dontnostttrt.s.l., harvest oI larvac of thc Sdutnrtosutrt s./. tn thc Carnoy for the cytotaxonomrc studrcs, capture and drssection o1' black flrcs, cleternrtnation of larvac stages of O. volvulus, conservation of parasrtes tor DNA analysis, rarsing ofblack [lrcs ft'onl tlte nynrPh stage, rcadrng of u,atcr lcvcl gauges, usc ol-t5e (]1,S, spraylng olinscctrci6c.IIo$'evcr. Mc-ÿcr (2000) satd tlre lirst p|r<lund trcirtnrcnt rvouki trc prcceclc<l br,'sci,cral rvccks ol r.c- 18 training of technicians on pre-treatment prospecting, experimcntal treatment, insecticidc tests, and hydro-biological activities. Dcspitc thc nunrerous dclays in signatures on documents, and thc late application of ordcrs anddclivery, most of thc matertal and equipment (except a 4 x 4), havc graduaily b".n procurcd and rnstalled at Malabo. Since the first ground treatment was scheduled for 2001, Meycr indicated that all the accessible rtvers bclow an altitude of 500 m be treated every 2 km, and twice a week. All the authors (Wilson, 1996; Bano, 1999; Mas et al, 2000; Meyer, 2000; Cheke, 2000) are unanimous on the fact that the ideal period for treatments is lïom January to April, for the hydrology, rainfall levels and black fly dcnsities arc parltcularly favourablc for a good trcatment exercise. The rnsecticide recommendcd rs Temep6os with an active matter of 20o emulsifiable concentrate, due to its qualities (biodegradable, withoui any toxic effect on mammals and fishes, moderate impact on non-target fauna, and good efficacious carrying capacity). The dose will be 0.3 Um3 of flow rate, hence about 1,200 I will be ,,à..."ry for the "u*puigi(Meyer, 2000). The latter proposes that to lessen costs, insecticide should be negotiaied and taken from OCP stock, which would include the quantiÿ required in its next order. It must be noted that in the event of very low flow rates, (lower that 0.5 m'/s1, it is necessary to increase the dosage, and this requires a greater quantiÿ of insecticide. To address this imperative, a stock of 2,000 I oi Temephos would be a good precautionary measure. Since the Bacillus thuringiensis Hl4 is being proposed ai the stand-by insecticide, in the event of resistance of the larvae to Temophos, Meyer (21000) deems the security stock to be 300 l. Treatment is scheduled to be carried out on the ground, but the inaccessibility of somc breeding sites could enkil the use of a helicopter. From the point of view of expected outcomes, Philippon (2000) notes that the frrst ground treatment operation should, at least, show the feasibility of a control in the norlhem part of the island, and at bcst, its isolation fiom the southern part. The timrng of re-colonization b), adults and larvae rvill have to be carefully monitored. In addition, the analysis of molecular biologl, should allorv lor the detemrtnation of the origin of new black fly populations. On the other hand, this ground treatnlent should not provide a lot of information on a possible aerial treatment. As a matter of fact, it is not obvious that inaccessible breeding sites on the ground could be treated by helicopter, due to the canopy. It seents, therefore, a bit premature to rush into aerial treatment. [t is only after analyzing the results of ground the treatment that a decision could be made. d) Conduct and results of Iirst ground trcatment operation Phrhppon (2000) states that at the end of 2000, base data that are nceded for control rvas available, local expertise was in place, an action plan was drawn up, and the tasks involved in this rvork s,ere entrusted to individuals, who were expenenced in this kind of operations. The first ground treatment operation took place at Btoko during the dry season (January-March) 2001. This was preceded by the collection of pre-freatment data on cytotaxonomy, the sensitiviÿ of the vcctor to insecticides, the drstributron of species (namely at altitude), and the rmpact of larvicidrng on rlon-target fauna. At the ttme of the works only 30 watercourses were flou,rng sufftciently to ntent treatment. As seven (7) of the watercourses have complex basrns (several snrall rnaccessrble tributaries), out ol the 248 proposcd spraying points, only 92 rvere sclectcd. The flow ratcs ol the rivers were lorver than I mr/s, and the water rvas clear (turbidrty<5JTU) and cool ( 190<240C). The personnel in charge of the spraying numbcrcd 10, broken lnto two teams, each of rvhich had a teaur leader, 3 technicians and a driver. lior easc of rnovemcnt, of thc stafl, APOC purchased thrce neu, 'l'tlvota IIrlux cloublc-catrrn vchiclcs lrvo trucks and churns lor lou,rnq vchrclcs In addrtrrtn, thc Spartrsh(.ooltcratton olÏcc put a Landover at tltc drsposal of thc team. In addrtron to the sltrayrng, thrs persor.tncl u'as ttrtegrated tnto othcr actrvrtrcs: capture and disscctron of black flrcs, hydrobrology rvorks, scnsrbilrty tcsts and prospecting o[rivers. Meycr (2000) notes that tlicsc u,orks should conrnbutc to startrng up thc caml)argn, rvhrch would combrnc ground trcatnrcnt u,rth aenal spraying. ! L9 The insecticide for the ground treatment is Temephos, and thc operational dose was 0.4litcrs/m3/s of flow, instead of o.l lÀrls as originally planned. îhis slight i.,crease is due to the prevailing conditions during trcatment: water tcmperature (100C-240C), u"ry lo* flow rates (io*", trrà" r-;i.ll[as[ current (0.3 at lm/s) and fast dispersion of insecticide. The latler was sprayed, thanks to spraycrs (5rn all) Bcrthoud Cosmos l8 type. This sprayer was selected for scveral ."u*n., it is easy to usc, itswcight makes carrying over long distances possible, it allows l-or rapid ,na simpie application ofrnsccticide, the quantity of chemical to bc sprayed could be measurcd with precision, and contact withthc rnsecticide does not corrodc the apparatus. To conduct the entire treatment, a stock made up of 2,000 I of Temephos, 500 I of Bt and 40 I ofRhodamine werc dispatched to Bioko. I{owever, to adàress the problem oi d"loy in stock delrvery, anadditronal I50 I of Tcmephos was sent by air, as matter of urgencÿ. Treatment started on l2 February 2001, and spanned five weeks, at the rate of one treatment perweek' The first two treatment cycles took 4 days to côver all the breeding sites. onlf .iu".s *ho.e flowrates were equal to or lower than 0.01m3/s were not included in the heatment. Tlius, 92 points weretreated each week, with approximately 2l liters of Temephos. of course treatÀni was planned for 12cycles, but it stopped after the frfth application, for technical reasons (mainly i.,r""..ribiliÿ of breeding sites). One of the objectives of the first campaign was to collect a maximum of information, following thespraying with Temephos, in order to appraise its efficacy in the operational conditions of Bioko. Fromthe several data collected, our conclusions are as follows: a) The insecticide carrying capaciÿ was 1 to 3 km, for flow rates going from 0.05m3/s to0.2m3ls- As Meyer indicated (2001), in the event of aerial treatrlred it i, to* carrying capacity will cause an increase in the number of flight hours, and hence an increase inbudget. b) The cycle of pre-imago development was partrcularly long (more than 2 weeks), for thetemperature of water was usually low (190C-240C). The re-colonization of supports after each treatment was, therefore, very slow. c) No pre-imago stage was harvested beyond an altitude of 500 m. On the contrary, adults rvere captured at an altitude of between 500m and 1,250 m.d) Adult population densities fell quickly after the starting treatment. Captures were nil at some points, after only 4 weeks, though no river rvas entirely treated. It should be noted that accessibility to the rvatercourses is very drfficult, and several tributaries cannot be reached. At the end of the first campaign, which was conducted in the northern part of the island, Meyer(2001) and Cheke (2001)' note that due to the inaccessrbrhty of some watercourses, ground treatmentalone may never succeed in eliminating the vector from the Bioko locus. on the other hand, thrs objective may be amved at, in only one season, thanks to an action of ground treatment coupled u,ith aenal spraying. This position was buttressed, follorving the aerial prospecting carried out in the southernpart of the island, and which revealed that most of thc nvers (some of which shelter the S. damnosum s'l') were partially or totally inaccessible on the ground. Thus, Meyer 2001) and cheke (2001) are of the vierv that ae.al operations are feasible for the follorving reasons: t' The stock o[Temephos at Bioko is sufficient for covcring a ground and aerial treatment;ir' An extenston of thc conhact betrveen OCP and the coipanl, in chargc of aenal treatment in Wcst Alrica should be fcasiblc;tir' 'l'he flrght hour, estimated at $1,030, the cost o[the aerial ol]cratror.r. rvould rise to $300- 400,000; tv. .l-[rc protcctcd Populatron rs estrmatcd at 75.000 pcople, rc. About 5 US doltars/,crso,, Irrom thc foregoing, and considertng the cessatlon of OCP activrtres at the cnd of 2002, Meycr and Chckc (2001) are of tlic vrcu' that if thc acrial canrparqn rs not carrrcd out i,2002, ApOC rvrll missthat golclcn opltorluur ty. 20 e) Problems and difficulties encountered at Bioko Various scientists have rcported a number of obstacles to the smooth running of activitics of the "vcctor clirnination project at Bioko". We arc mentioning hcre those that still n"""a to bc addresscd(Mcyer,200l): - The movenrcnt of teams is often difficult, due to pohce and military check points. The securiÿ agcnts don'L seem to have undergone any good sensitization. - Working relations are particularly difficult with the NOTF Coordinator, hence the numerousproblems that might hamper the chances of success of the control effort; - 'fasks are distributed in the national team in such a way that thc absence of an employec(cspccially the NOTF coordinator) may impede thc smooth running of the outht; - The national team may be effective, but it needs discipline and supervision of its activities. These two aspects are, most of the time, lacking. f) Prevalence Mas et al (1995), following an epidemiological survey conducted on the entire island, mention that average prevalence was75%o (85% inpersons of over 15 years). The population at riskwas then estimated to be 62,000 people. Epidemiology is the forest ÿpe, characterizedby 0.g% of blindness, 3lyo of nodule carriers, 29%o of carriers of dermatological lesions, and lympho-adenopathics estimated at42%. Most of the villages are found in the northern part of the island, at )-l km of the sea. Onchocerciasis prevalence is high in all the areas. It is 76.5Yo at Basapu, located at km only from Malabo. As for the highest prevalence (87.1%), it was recorded at Ureca, in the southem parr of the island. An epiderniological survey, conducted in 1989 (Mas et al.) with a population of 1759 inhabitants from l2 r'illages, enabled a prevalence oî74.6% (hyper-endemic) to be recorded. In 199g, after 9 years of ivennectin dishibution to the inhabitants of the same villages, the rate of prevalcnce was only 3-g-2%(hypo-endemic), for a population of 1,167 inhabitants. The same goes fàr the percentages that are carriers of nodules and dermatological lesions, rvhich fell by 2.8o and 7.97o respectively. g) Isolation of the island The vector control activities can only be undertaken ln an isolated focus (Walsh, 1990). That of Broko has a number of criteria for geographical isolation: the closest sources of re-invaston are the neighbourhoods of Mount Cameroon, located in the northeast, and part of the Cameroonian coast in the East. The distances from these paces are 40 kni and 80-130 km respecttvely. The Atlantic Ocean is in the West and South, where thc Principe Island (240 km), Sao Tome and Anabon are found. The latter has never sheltered the S. damnosttm s.l. (Mas, unpublished), and the black flies have not been examined on the other two islands (Santos gracio, 1990). The meteorological conditions severely impede the movement of black flies from the contincnt toward the island. Actually, almost all year round, dominant rvinds, coming from the South or South West, blow across the island toward the continent. Even rn the drrest period of the dry scason, hardly does the rnter-tropical convergencezone (ITCZ) gct to the island (Teran, 1962). I{aving black flies comc from the north or east rs rnrprobable, becausc thrs will be rn the opposrte drrection of the domtnant winds. The cytotaxonomic (Boakye, 1993), cyro-gcnctrcs (wrrson and post, 1994), and Irtorphtllogical crttct'ta (Wrlson, 199(r) rntlrcatc tlrat thc black tll,population ollJrok6 rs cssentrally rnadc up of thc S. vahcnse, Ilroko typc. Arrd yet any possible rc-lnvaslol could orrly cotne fronl thc Calneroontan coasts, rvhcre the .S. Squatnosutn and S dumno"^ttttt s.1. species are found. TI.us mcans tlrat thc Bioko population is gcnetically rsolated. 2t h) Impact of trcatnrcnt on thc cnvironment Brooks and Jackson carried out a survey on the Bioko island in March-April 1999, to determine tlic drstribution of Odonatcs. The results indicate that the l7 sites visitcd are located at altitudes of 1,500nr,600 m and below 500 m. Few odonates (47) at the larvae stage were harvested. This sample(before treatment: 22; after treatment: 25) does not help assess the effect of the Tenrephos on this Sroup.On the contrary, 260 adults representing 24 species, including 6 new ones, were harvested. Distribution is 6 specics encountered solely above 500 m, l7 below 500 m and l3 in both sites. It must be noted that out of the 2l 1 draqonflies recorded on the island, only 7 were found during the sun,ey. A study of the impact of larviciding with Temephos against the S. damnosum s.l. on frshes and shrimps of Bioko, was conducted in the dry season (March-April). Abban (1999) notes that fishes encountered during the survey included 12 families, 21 geneva and 25 species. Ouiof this there were only 9 freshwater fishes whose populations would be exposed to larviciding effects The small-size species made up the majoriÿ of fishes. The shrimps were particularly numerous in all the rivers. Theirbehaviour and reactions were normal. The same goes for the doses of 0.5, 0.25 and 0.125 mÿI. However, a fish, exposed to doses of I and 2 mgll showed disorderly movements, and ended -up becoming stationary in some minutes (2-5). However, the transfer of individuals in a stationary phase in water without insecticide revived them in less than one hour. As for the experiments conducted with high doses, they show that all the fishes exposed to doses of 30 and 15 mg/l ài.d i. less than one hour.At doses of 7.5 mg/l and 3.75 mgll, the time of survival was 12-24 hours and more than 24 hours, respectively. The distribution of the macro-fauna was studied on l0 rivers of the Bioko island (Amase and Amegbe, 1999). The aquatic fauna was regular and generally more abundant belos, an altitude of 500 m. The effect of Tcmephos on the latter, rvas monitored on the Ruma, Musola and Apu rivers located in the east, west and northwest respectlvely of the focus. Out of the three sites, the use of Temephos led to a reductton in the number of chtronomides, but re-colonization is relatively faster. The erthoclamidae were the most affected by the rvave of insecticrde, while the Tanipodinae were less affected i)Training At the end of the vartous missions, it appears that the local staff benefited from theoretical trainrng (background on onchocerciasis), and rvere initiated, on several occasrons, on the use of the technrques applied in the area of vector control: larvae prospecting, capture and dissection of femalcs, estimation of the flow rate of a river (with or u,ithout a gauge), calculation of insecticide doses, using thc flow rate, ground larviciding of black flies, and pre/post treatment monitoring. 4.2.3. CDTI status in the focus Thc population of the Bioko Island is estrnrated at 90,000 inhabitants in 68 communities. CDTI has to do with 61 communrties located in hyper and meso-endemic areas. The target population is about 60,000, half of rvhich lives tn the torvn oI Malabo. Be fore instituting the ApOt i.ogru-*", all thc comnrut]tties \^/ere receiving ivermectrn, based on thc vertrcal approach. But gi'en thc commitntent of the govemment, and the good drsposrtion of the population, the CDTI approu"h .*,u, adoptcd in 2000. Training of the techntcal stafl- tnvolved rn rvennectrn drstnbution was initrated. Sensitizatron \\,as conducted u'rth the populatron to cxplarn thrs neu, rnodc oldrug clrstributron. 'l'hc rcsults ol lhc sccontl ycar of'treaturcllt rn<ircate that out ol 18,22-1 persons, 7.582 rvere trcatcd, r.c. a thcrapcutrc covcrlrqc rate <tf 42o/u. I'hc populatron treatcd is bctr,,,cen thc drstricts of Malabo (2928 persons), Ilanrcy (2270 pcrsons). t-uba (1575), and Rraba (809 persons). For thcse same drstricts, thc gcograplttcal covr'ragc- rs 100%,81oÂ, 100%, and 937o rcspcctively. Abientccism rs high, lor thc trrhabttants are aû-atil tll- llte srclc cflècts <ll' n'crrncctrn. Vcry c[lectrr'.- scnsitrzation shttuld conLrrbtrtc to utcrcasc tlrc varrtlus c()\,cratc ratcs. 22 4.2.4. Budget for vcctor elimination activitics To allow for thc start-up and continuation of vector elimination activitics, thc ApOC progranlme provrded regular financial assistance on the basis of letters of agreement (Contracts). The table belorv surrs up the budget component of tlie project. Period covcred Cash transferred To field in $US Amount expenscs in SUS 0 Purchasc equipmcnt C Total cost March 99-Fcb 00 21,984 I 6,61 8 168,490 185 r08 March 00-Feb. 01 54,776 25,436 124,660 150 096 March 0l-Feb 02 55,390 NA 136,400 136,400 Total 132,150 42,054 429,550 471,604 4.2.5. Discussions - Remarks a) Distribution of S. damnosum s.l. The southern part of the Bioko Island, about 40% of the total area, is inaccessible. On the contrary, several prospecting activities have been carried out on the accessiblc part. These prospecting activities were carried out the whole year, but they were mainly concentrated in the dry season (mainly in January to April), the ideal pcriod for treating larvae breeding sites (Wilson, 1996; Barro, 1999; Meyer, 1999; Meyer eL al; 2001). Despite the great number of rvorks, the results of all the authors aqree on several points: The ,S. darnnosum complex is represented on the Bioko island exclusively by the S. yahense, Bioko ÿpe; Rivers are numerous and short (averaging 7 Km long); Watercourses, protected by luxuriant vegetation, are hardly accessrble; In the dry season, the flow rate of rivers are generally below lmr/s. Water is clear (turbidiry<5 JTU) and cool ( I 9oC<temperature< 260 C); The pre-in,ago breeding sites below an altitude of 500 m, are generally positive, when the tcmperature of the water is higher than 2205C. No pre-imago stages have been harvested beyond 500 m. On the other hand, adults have been captured at altitudes of betrveen 550 and 1,250 m. It is agreed that vector elimination in a grven focus is only possible if all the breeding sites are subject to larviciding. However, thc results of the various prospecting carried out at Bioko indrcate clearly that the rivers arc very numerous and protected by dense vegetation. This means that a number of breedrng sites remarn unknou,n, due to the inaccessibility of u,atercourses. This situation also poses the problem of choicc of spraying points. It must ensure a-100o coveragc of all the breeding sites. Of course , the authors agree that malonty of the positive breedrng sites are located beloq, an altitude of 500 m. I{owever, the presence of adults between 550 and 1,250 m risks undcrmining the chances of success (possiblc re-invasion), sincc the area located bcyond an altitude of 500 m is excluded from larviciding. Besidcs, following the prospectrng undertaken in the southern part of the Island, Meyer (2001) notes that apart from the Musola Iliver, and rts tnbutary, the Eba, no rivcr rvas acccssible beyond an altituclc ol-500lll ltvert ltclorv 50() In, scvtral \\'atcrcourscs tt,cre llartralll,or contplctcll,rnacccssrble T[is 1rcals that no nvcr could bc trca(ccl on tts entlre coursc. :I 23 b) Isolation of the Bioko focus The authors are unanimous in agrecing that the Bioko focus is isolated. In actual fact, it is anisland whcrc meteorological conditions (especially wind movement; Tcran, 1962; Nasti, 1942) hamperthe rc-invasion of the focus. Besides, cytotaxonomic (Boa§e, 1993), morpholâgilut lwitron, 1996)and cyto-gcnctic (Wilson and Post, 1994) evidence make one recognize thàt tn"-S. yahense found atBioko is differcnt from thc standard ÿpe. There is therefore, a geietic i.otrtion,î.'"o*pu."d to the nearcst black fly species, and those found on the cameroonian coasts. c) Vector control Rtvcr tcsts rcvcalcd that the selected insecticide for the treatments in field conditions at Bioko, was Temephos with active matter of 20% emulsifiable concentrate. The experiencJgainea during thepreliminary works, indicate that the vector elimination project at Bioko wàuld i,c.ease its chances ofsuccess, if control operations started in the dry season, and spread over 34 months. At the usual operational doses, the spraying of insecticide is followed by a reàuction in the number of chironomidae,but the re-colonization is relatively fast. On the other hand, fish and shrimp popufurion, are not affected(no mortality; normal behaviour) by the insecticide treatment. This means tËat a t àuon"rrt campaign against pre-imago stages of the S. damnosum s.l. through Temephos spraying in the watercourses of theIsland of Bioko should not have irreversible negative con."quln"., on-the non-target fauna. (Abban,1999), notes that there is a very large gap between the operational doses and the tox"ic doses for fishes and shrimps- However, since the first campaign came off in 2001, it is necessat;;* to undertake apost-treatment collection, in order to assess the impact of five treatment cycles o., ih" aquatic fauna andthe environment. Besides, since some positive breeding sites of the Grande Ruma and Musola Rivers are inaccessible on the ground, their treatment could be subject to aerial treatment. Given the OCp experience, Meyer (2001) and Cheke (2001) recommend the helicopter as the best means for giving theindispensable support to the total coverage of all the breeding sites. This option seems buttressed by thefact that in the south of the island, several watercourses shelter the S. damnosum s.l. which were totally or partially inaccessible. As Seketili (200I) indicates, the fact remains that the use of the helicopter supposes, first of all, responding to a number of questions: - has ivermectin been distributed over the past l2 years? - What is the cost of aerial an operation? 300400,000 US dollars, as recommended by Meyer(2001)? It must be noted that parking rights, and transfer costs of the aircraft are not taken into account in the amounts mentioned above. The same goes for the cost of entomological evaluation, and the cost of tickets, per diem, insurance, etc.. of extemal persons (experts and scientists), who will be involved in the operations; - How many persons will be protected by this operation? For information purposes, the targetpopulation of the island is about 60,000, half of who live in Malabo. There is need to recall that the JAF6 had recommended that the decision to carry out aerial treatments rvould only be after a close analysis of the results of the first ground treatment. d) Entomological evaluation The PAT and ATP are good indicators of the entomological situation, for they quantify the blackfly aggression and the transmtssion of the O volvulus respectivày. On the island of Éiàto, and from the captures made in 1992, Wilson (1996) notes, that apart from the dry season (from January to April), theblack fly dcnsities are high. Thc period from Septembcr to November remains that when the black flics arc most abundant- However, Anonymous (2000) and Cheke (2001) record MBRs between I305 and11,475 in April-May, and bctwcen 2970 and 10,380 in February. This means that evcn in the dry scason, the black lly dcnsr(ics nray be hrqlr. Givcn that thc black fly speclcs involvcd rs the S. claltltrosut.t-t s.l;, it rs probable that thc ralny season rs whcr.r aggressrvencss rvrll be nraximal. Irrom 1996, it has bccn cstablishcd that the fenrales of the S damnosum s.l. captured on the rsland o[Broko had high tnlcstatron ratcs (wilson, 1996). [n effect, the percentage of infectivc females(tlrose susccptiblc lo transnlt thc Parasitc at tlre ncxt brte) was 14.60Â. O.ly th"e numbcr of drssectedIi'rllalcs (56) at thc timc, was arl rrnpcdirncnt to an cnhanced intcrprctation of the results. Thc latter arc, 24 nevertheless, confirmed in 1999 by the dissection of 878 females, which reveal Myo of infected females and 80 of infective females (Anonymous, 1999). Of course the ATP could not be established for 2000,but the MTPs obtained in April and May at the various points of capture arc by far higher (MTp minimum = 130 at Balacha; maximum = 473 at Musola) at the tolerable threshold of tOO LilÀan/yàar in thc savanna zone olWest Africa. The works of Cheke (2001) corroborate the previous results, because apart from the points of capture located at altitude (0<MTP<72), all the othcr MTps are higher than 100(minimum = 3 l9 at Sampaka; maximum =- 127 5 at Musola). The various works of authors agree on this, and indicate that the transmission rate is high on thc Bioko island. The infestation rates recorded recall those recorded on the small rivers of forest areas in West Africa, where the vector is also the S. yahense. From our reference to the results recorded in 1989 and 1998 (Mas et al), it clearly appears that alter 9 years of lreatment with ivermectin, prevalence had gone from hyper-endemic ea.6%j to hypo- endemic (38.6%). Such a change usually tells on the level of black fly infestatron. This assumpti;; is corroborated by the results of some authors. Thus, from Geenen (1993) to Mas and Tirados 1ZOôO1, ttre number of infecting larvae for 1,000 parous goes down from 400 to 74, and the MTp from 1600 to 15. On the other hand, this is not the case, if we refer to the infestation rates recorded by Cheke (2001). The absence of pre-imago stages should mean the exclusion of breeding sites located beyond an altitude of 500 m, from all treatment campaigns. But the adults wee captured between 550m and 1,250 m. The eggJaying points of these altitude females remain to be determined for setting the limits of the area to undergo larviciding. [n effect, these females may come back to lay eggs in the breeding sites located below the 500 m altitude, as prospecting may not have been precise (abundance of brJeding sites, difficult access to rivers, due to vegetation) for detecting the positive breeding sites located beyo.,à the altitude of 500 m. 4.2.6. Conclusions - Suggestions Apart from the feasibiliÿ srudy conducted in 1996, several surveys rvere carried out on the Bioko island between 1996 and 2001. The objective rvas to collect indispensabie data for conducting treatment campaigns and their evaluation. The first campaign of ground treatment took place in February-March 200 1, and the various outcomes, in relation to the set objective for vector elimination, enable the following points to be established: The geographical situation, meteorological conditions and the cyto-taxonomic, morphologic and cÿo-genetic criteria conf,rrm that the island of Bioko is an isolated focus. Given the distnbution of rivers and the prospected breeding sites, it appears that to each prospecting corresponds at least a new breeding site (discovered on a river that is already fisted or not). Besides, the presence of adults at altitude, places the treated zone under the menace of re-invasion. This situation poses the problem of total coverage of breedrng sites by insecticide treatment, rvhich is an indispensable condition for vector elimination. [t therefore, seems preferable to plan the treatment of all the rivers that have sufficient flow to favour the settlement of pre-imago stages of the,S. damnoswn s./. In view of this, punctual investigations should be undertaken to make up for the lapses or the lack of information on the mapping of the breeding sites, the spraying points and the accessibility of breeding sites. The geographical configuration (namely vegetation cover), is such that, apart from a fcrv exceptions, larviciding wrll have to be carried out by ground spraying. Portablc spraying machines (Berhoud ÿpc) would be the most efficacious, for they spray out the mcasurcd quantities of insecticide. 'the ideal period for larvrcidrng u,ould be the beginning of the dry season, whcreas the florv rs still sufficient for a good carrying capacity of the insecticide. The "brccdrng sitc by brecdrng site" treatmcnt could, thus, bc avoided, and thrs u,ill bnng about a nrultrplrcatron ol' sprayrng pornts. l'lie black fly dcnsity on thc Bioko Island rs usually abundant, and transmission rs cxclusively ensurcd by thc S. yalrcnse, Bioko type. The vector characteristrcs (infcstation ratcs, parasitrc loads) rccorded arc hrgh and recall those observed in the forest arcas of Afnca, rvhere the S. yultensa ts also thc r.narn vcctor. t a a 25 The base data and those of impact studies on the environment of the Bioko Island, in relation with the treatment with Temephos, will be indispensable during the evaluation of the control activitics. The collection works must thereforc be continucd. Thus, flor a better knowledge ofl.he non-targct entomic fauna, Yameogo (2001) notes that it would bc desirable to havequalitative sampling of the vegetation (leaves, immerged dead wood), and the under-gravel.Besides, thc high predominance (75%) of the Elmidae on the Lada river, necessitatesinvcstigations on this family and its living environment. On the other hand, the option of organism indicators (namely Odonates), for monitoring thc impact of treatment on the non-target fauna, needs to be reviewed. The same goes for the seleciion of perennial watercourses, which would not be treated to constitute refuge zones. The latter would shelter, not only non- target fauna, but also the vector. Thc local staff, called in to undertake implementation and monitolpg of vector eliminatio' activities' was identified and selected. Staff members had punctual trarlning during the ua.iousinvestigations that were carried out on the island of Bioko. Regular "îutuutiin itechnicalknowledge, professional conscience), followed by re-training, if necessary, is desirable for this staff in order ensures continuiÿ and efficiency of control activities. For example, the results ofApril and May 2000 indicate that the computation of infestation rates (% oi infected parous females, % of infective parous females) and indices of transmission (MÈR, ABÀt;;; still not very well assimilated. It is clear from the various investigations mentioned in the reports that the activities of the local team stop, sometimes immediately it is alone in organizing fieldwork. It u,ould be desirable thatpersonnel be sensitized so that the relational issues involving individuals and/or instiiutlons ao not hamper the smooth running of control activities. To ensure monitoring of routine activities of the national team, it would be proper that the coordinator of the project solicit a progress report, on a regular basis, and be morè pàsent on thefield. 26 4.3. ITWARA FOCUS Uganda is one of the first countries, where onchocerciasis vector control was successful. Thus, thc.S. r/arrurosurn s.l. was eliminated from the Victoria Nile focus, and thc S. rreo,ei temporary kicked out o1'tlre Budongo locus (Prentice, 1974). In the 70s, the use of DDT with active matter of 25%o of emulsifiable concentrate, helped tointemrpttransmissionofonchocerciasisinthefocusof Itwara(Garmsetal., 1994). Duetotheabsence of funding, and the insccurity, control efforts stopped from 1975 to 1971. But in 1990, nerv fundingprovidcd by the German Cooperation (GTZ), and the Ministry of Ilcalth of Uganda, enable datf collcction to continue (Garms et al., 1992). It is under this that all the rivers susceptibte to shelter the S. neavei.s..§. were prospected and the adult population monitored, thanks to the captures, dissections and determination of infestation rates (Garms et al. 1994). The spraying of Temephoi, which as carried out from August 1995, were found to be efficacious, and the results promising, aftLr only 3 treatment cycles. In effect, between 1994 and 1995, the black fly densities went down from 481 to 0 àn the Kijura biidge, and from 365 to 2 at Busasa. Given these results, teatment was extended to the main breedi.,g .it".ii the focus that shelter the S. neavei. The elimination of the vector from the Itrvara focus became an attainable objective. To safeguard its gains, and to contribute to the elimination of the disease, the Technical Consultative Committee (TCC) approved the surveillance and continuation of larviciding of the breeding sites of the focus of ltwara, and all the foci of Siisa and Aswa. This choice is part of-the objectives of APOC, which in some particular cases, is onchocerciasis control, through vector elimination. From 1996, the focus of Itwara was selected, because pre-treatment data was available, and qualified staff and control activities were already ongoing. 4.3.1. Prcscntation of locus The Itwara focus is located around the forest reserve bearing the same name, at about 25 Km in the nofth of Fort Portal (fig. 17). The reserve covers about 20 sq Km, 22o of u,hich are made up of trce vegetation (Howard, 1991). It is bordered by large plantations of tea, subsistence crops and ranchcs along the rivers (Sogohi, Kahamba, Muzizi, Mpanga). This is to say that the original forest has been extensively cleared for the sake of plantations. The rvatercourses are, nevertheless protected by dense forest galleries. The landscape is characterized by rvooded valleys and mountains with altrtudes varying betrveen 1,250 and 1,460 m. Tempcratures are, therefore, moderate. The climate of the area is characterizedby a humid heat, and all-year-round rains. Maximum rainfall figures (1,000-1,400) are observed from September to November. The dn,season stretches from Deccmber to February, but it is never totally dry. Hydrological condrtions are generally favourable, all year round, for the development of pre- inrago stages of thc S. neavei. The larvae breeding sites are found essentially on the §ogohi and its trtbutaries (Wamisc, Nyakrbuguta, Kanaba, Kafunda), the Srisa and rts tributaries (Kyasa, Mohabura) and finally the Asrva River. The area rs densely populated, and onchocerciasis is highly endcmic hcre. [n 1997, 80% of thc 45 lrcrsrlns u'ho livcd in the ncighbourhood o[ the forcst rcscrr/c. \\rerc iufcsrc-d by tftc O t,olt,ulu.s((iar nrs. 1 997). 'fhe black fly spccrcs to cltnrtnatc from the locus rs thc S. neavci s.s., the nrain onchoccrcrasis vcctor (Barnley and Prenttce, 1958; Prentrce, 1974; Ganns et al., 1992). It flyrne capacity is about 6-10 Krll. Thc lrlespan of thc larva is 3-4 wecks, due to the rvatertempcrature, u,hrch bctrvcen l8oC an6 19"C. I 27 4.3.2. Nature o[ Works 'l'he works carried out frorn 1970 to 1997 (cspecially in 1994) in the ltwara focus , dweltcsscntially on - Dynamics of pre-imago and imago populations; - Determination of the duration of pre-imago development; - Vectoridentification; - Distribution of breeding sites with the S. neavei in and around the focus. - Vector characteristics of the S. neavei; - River tests of the Temephos (determination of doses and carrying capaciÿ). - Training of pcrsonnel. As part of the works carried out, with the support of APOC, the national team, in charge of the vector elimination activities, undertook intense activities of surveillance and supervision, in-order to ensure that vector collection is properly done. The activities are summed up as foliows: - Regular prospecting of the main contol points in the main ltwara focus, and in the sub- foçi of Aswa and Siisa; - The capture of black flies at pre-selected points; - The treatment of rivers at intervals of 4 weelcs, in the sub-foci of Siisa and Aswa. 4.3.3. Rcsults obtained a) Prospecting breeding sites The entomological data collected between 1991 and 1994, prior to instituting treatme,t rvitlr Temephos, tndicatc that 38.9% of the crabs captured on the Sogohi river (Itu,ara folus) carried pre- imago stages of the S. neavei. Though treatment rvas discontinued on the rivers on the western side of the ltwara focus, Garms(1997), it must be noted that the latter were not re-invaded. Since the last crabs were found to bepositive at Nyakibuguta in August 1995, the river was treated in December 1995. Nevertheless, the 479 crabs harvested at Nyakibuguta in 1996-1997 were all negative. Besides, none of the l6g3 crabs fromltwara' Srisa and Aswa carried pre-imago stages of the S. neat,ei. The last crab sheltering only one larva of the S. neavei dates back to November I 996, and was harvested on river Sogohi .. The prospecting carried out in May, June and October 1997 in the Itwara focus made it possible to catch 871 crabs, none of which carried pre-imago stages (Lakwo et al. 1998). The same goes for the 50 crabs harvested at Sogohi in February 1998. The Srrsa and Muhabura rivers were also prospected in May, June and October 1997. Out of 614 crabs examined, only 2 carried larvae of the.S. neattei. From N4arch to June 1997, thc sub-focus of Aswa u,as treated with l7.5 I of Temephos. Laku,o et al. (1998) cstabhsh that the post-treatment control conductcd in May, June, August and October enable the sampling oi585 crabs, l5 (2.6%) of rvhich wcre carrying pre-imago sta_ccs Jf tn. S. neayei. In Ivlarch 1997, (Garms), about 900 crabs fronr the Itwara focus u,cre eramined, and all rvcrc ttt'q:lllvc (lttl trllcctrttrr b1'thc S. ncavct). 'l-hc sanrc ucnl for 494 crabs harr'.,srcd r' thc sub-lbcus tll- srrsa. ()n thc- contrary, rn thc sub-lbcus o1'Asrva, tl.rc crabs u,erc infcstcd. In Oclobcr 1991,354 crabs wcrc harvestcd by thc national team in the sub-focus of Srisa (179) and Asrva (175). and 2 (l%) and 4 (2"Â) rcspectrvely, carrred larvae of the S. tteat,ci. 28 From September 1998 to September 1999,7 rivers were prospected in the ltwara focus by thenational team- The 872 crabs captured were all negative. During the same period, only 0.3% of thell84l crabsharvestcdinthesub-focusof Siisacarricdpre-imagostagesof the.s. rteavei. ontheotherlrand, in tlte sub-focus of Aswa,6.l% of the l6l6 crabs examincà were carricrs of the S. neavei. In 2000' the 6 prospecting sessions carried out in the focus of Itwara by the national team helpedto harvesL 5Sg crabs; all were dcvoid of pre-imago stages of the.S. neavei. During t6e same period, 1479crabs harvcsted at Siisa were equally all negative. on the other hand, ne ç7;1"1oi,i,.3674 crabssampled at Aswa were infested with the S. neavei. The infestation rates varied from I .2,yo to l9oÂ. Itmust be noted that before larviciding, 80.4% of the 92 crabs caught on thc Musabira River were positive, whcreas just after 4 treatment rounds, none of the 470 crabs exÀined carned pr"-lnlrgo stages oI the .s.ttctt't,ci. Between January an August 2001, the prospecting of the national team made it possible toharvest 4656 crabs in the Itwara focus (948),630 in-the.ù-fo"u. of Siisa, and 307g in that of Aswa.No pre-imago stage was found on the crabs of Itwara, and only one larva of ihe S. rteaveiwas taken froma crab (0.2% of the population) from Siisa. The highest raté ç0.+u"1of positive "."Ù. *", observed atAswa. b) Captures-Dissection-Transmission The adult capture sessions were less than larvae prospecting. Nevertheless, the following couldbe noted: In 1994, prior to starting larviciding, the dissection of 2889 parous females revealed 622 infected females (24%) and 120 infective ones (4%). Larviciding camed out from June to August 1995 brought about a drop in the blackfly density (table ll). It wenr lrom4gg2 in lgg4 to 3g04 in lgg5, and to 6 in 1gg6, at the capture point of Busasa. The same data gave 6403,2546 and 0 at Kijura and 2390,64 and 0 at Sogohi. ln March 1997 , it was estabhshed that the drstribution of ivermectin only intemrpted transmission partially. In effect, out of 153 parous females examined in t99t, 27.89% were infectedand2.60 rvere infective. In 1992,1993 and 1994, the same data were 684ll3|yol5.6oÂ, 399012G.8%13.5o and 3ol7lzl.g%/3.1% respecti'ely. The number of infecting lanae by 1000 parous females rvas 124 in 1991, 2j6in 1992,169 in 1993 and 176 in 1994. The data collected at Kicheche show that afrer 6 years of distribution of ivermectin, transmission was still intense. ln effect, out ofll5 parous females, 48 (42%) rvere infected, ll (9.5%) rvere infective, and the number of Lil1,000 parous ones u,as 470. The captures made in the Siisa focus in May, June and october 1997, were all negative. Besides, as of February 1998, no adult of the ^!. neavei had been capturedfor two years in the Itwara focus. The same goes for the sub-focus of Aswa, where the captures were nil from september 1998 to september 1999, at the capture points callcd Andrew and Tourist. Lastly, thc cntire 2000 was marked by the capture of negative catches of the S. neovei, at the drfferent capture points of thc Itwara focus, and the sub foci of Siisa and Aswa. On the other hand, 140 S' dttmnosunr .ç./. rvcre captured in the focus of Itrvara (39 females) and I I I females in the sub-focus olAswa. 'flrc dissection o[thesc females drd not reveal any infectron due to tbe O. volvttltts. c) Larvicitling Thc first cxpcrttnents werc carrtdd out by Garnrs rn August 1994 on the Sogohi rivcr, lor assessrrlg the cfficacy of thc Ternephos, and the Bt I'll4 rn the control of thc S. neaver (fig lg). Thet'csultshoq'cdthatat adose of0.l mg/l,Temephosdocsnotelrrninateall thelarvaeofthcs.neavci ovcr l<lrlg clrstanccs. Orl thc othcr hand, conccntratlons ol0 2 and 0.4 mg/t gave bctter results, rvhilc havrng t a 29 no negative effects on crabs. The experiments with the Bt did not give any good results, due to the low carry capaciÿ of this insecticide. In the ltwara focus, the last treatment with Temephos dates back to February 1997. It rvas carricd out on the Sogohi River. But treatment on thc other rivers of tlie focus rvere suspended much earlicr. Thus, the last treatment on thc Nyakibuguta dates back to Decembcr 1995. For the entire larviciding carried out in the ltwara focus, and its sub-loci of Siisa and Aswa, 160 liters offemephos were used from 1994 to 1997. Since this date, punctual treatments have been undertaken in the sub-foci (Aswa, especially). Thus in 2000, 58.75 liters of Temephos were used in the sub-focus of Aswa. The latter was also treated between September 1998 and December 1999. The monthly spraying was carried out at Andrew's pt, Guaging pt, Tourist pt and Tonrs's pt. It nrust be notcd that for logistics reasons (lack of insecticide), treatment in the sub-tocus of Asrva only started in 1997. d) Isolation of Focus The Itwara focus is not totally isolated from the two sub-foci, located around the Siisa and Aswa rivers (Garms, 1997). On the other hand, the entire set (focus and sub-foci) is at least 100 Km from the nearest breeding site (Kashogi-Kitomi focus). Besides, the latter shelter mainly the S. neavei, whose flying capacity is reduced (6-10 Km, maximum) e) Impact of treatment on environment It has been proved that Temephos, at operational doses, is without toxic effect on mammals and fishes. However, its impact on on-target fauna is moderate. At the end of observation carried out in Uganda, Garms (1991) establishes that crabs of the foci and sub-foci of Itwara, Siisa and Asrva, u,ere not affected by the operational doses of Temephos. I{owever, special studies on the impact of treatment on the environment were not conducted in thc vector el imination zone. f) Training Staff rraining was carried out dunng the several works carried out between 1970 and 1997(Garms, l99l). In 1998, the needed staff for the running of APOC activities u,as ayailable, qualrfied and experienced. 4.3.4. CDTI status in Focus The ltwara focus is located in the district of Kabarolc. tn the latter, covered by phase 2 ol the CDTI in Uganda, the total population of the endemic zone is 82,597. This populatron is distributed over 147 communrties, 120 of which are in a hyper-endemic zone, and2l in a meso-endemic zone. In 2000, the rate of therapeutic coverage was'tZo (58,121180,191), and in 2001, it was 73o (60,235/g2,597). Of course the target population of the district is known, but rt is also indispensable to determine that of the focus. This precision would enable a monrtoring of the evolution of the therapeutic coverage rn the focus, and to assess the impact of ivermectin there on onchoccrciasis transnusslon. 4.3.5. Budgct for vector clirnination activities 'l'o enablc vcctor elrmtnatton acttvtttes to contrnuc, tlic AI'OC l)rogranrnte ensurcd a rcgular financral asststance on thc basis of lettcrs o[agrcement (Contracts). The table belorv sums up thc budgct compor)cnt ol thc projcct: t 30 Covered Period Cash hansferred to field US$ Amount spent in US$ Purchase equipmcnt o Total cost Feb.99-Aug00 1 6,1 57 l s,9l7 12,029 27 946 00 I 10,951 NA 12,2gg I Total 27,108 15,917 24,327 40,244 4.3.6. Discussions-Remarks 'l-he rcsults of thc various prospecting works agree and indicate that rvhate'er the focus (Itrvara) or sub-focus (Siisa and Aswa), the treatment of the breeding sites with Temephos brings about a drastic reduction in the numbers of the pre-imago populations of the S. neavei. Even wîen treatment isdiscontinued, a drop in densities is recorded. The post-treatment controls indicate, however, an almost total absence of positive crabs, since 1997 , in the ltwara focus. The same goes for the sub-focus of Siisa since 2000. This means that the entire breeding sites of Iturara and Siisa àre under larviciding. On the other hand, the presence of positive crabs in the rivers of the sub-focus of Aswa, reveals the plesence of non-treated breeding sites. The latter must be listed and included for treatment, for only tot l "o,r"rug.of all the positive breeding sites would make it possible to envisage vector elimination. This objective is achievable, because it is enhanced by the fact that the area to be cleared (Itwara focus, Siisa and Aswa sub-foci) is isolated from the other onchocerciasis foci. In effect, the nearest foci are found at 100 Km and shelter essentially the S. neavei, whose flying capacity does not exceed l0 Km(Garms, 1997). Besides, the authors are unanimous that Temephos, given its qualities (efficacy, good carrying capaciry, moderate effects on non-target fauna), is the sclected larvicide for ground treatment ol the breeding sites oIthe ltwara focus and its sub-foci. The first factor that conditions the existence of the imago population is the pr-imago population. Sincc the latter is very sensitive to larviciding (Anonymous, 1985), this brings abôut a reduttiàn (even disappearance) of the adult population. The results obtained at Itwara, Siisa and Asrva are in lrnc with this rule. Lr effect, since treatmcnt started in 1995, black fly densities (5. neavei) dropped to zero in 1996 at Krjura and Sogohi. As treatment took place, the trend heightened, since no biting female rvas captured in 2000 on the entire focus (Itwara, Siisa, Asrva). The results recorded in 2001 confirm the absence of biting females in the area. It must be noted here that prior to larviciding, the black fly density reached I 9,000 bites/manL/year. From the viewpoint of transmission, the dissectron of females captured before larviciding reveals high infestation rates in the .§. neavei (% infested females : 24"/.; %o infective females : 4%t Besides, after 6 years of ivcrmectin distribution, transmissron was always intense at Kicheche (r of tnfectedfemales:47oÂ;o%ofinfectivefemales:9.5%;470Lill,000parousones). Thesedataconfirm the hyper-cndemic nature of the Itwara focus, and of its sub-foci (Siisa and Asrva). They also corroborate the observations of other authors, who assert that ivermectin does not totally intemrpt transmission. 4.3.7. Co nclusions-Suggcstions -fhe rcsults above indical"e that the treatment of the ltrvara locus and t]re sob-foci of Srrsa and Asu'a hclll to clrminate thc vcctor in this rcgton <lf Ugan<ja. It is therelore rmpcratiye to cont,tue qround tlcatlllcllt, csllccrall;' rrt thc sult-lilcus ol Asu,a, uhicli reniarns actrvc (punctual l)osltrvc brcc'drng srtcs).In cflect rts proxrrnrty ts such that black fltes can casily reach thc ltwara and Siisa brccding sitcs. 'lhe lattcr will have to continuc to bc surveycd with prccisron, during the penods considered to be of high black fly productrvtty, tn ordcr to confirnr that black flres are effectively and definrtely absent from the sard focr t 31 Of course bibliographical data indicate that the S. neavei has difficulty in reconstituting itspopulations when they have been greatly reduced. But the fact still remains that any interruptiJn intreatment contributes to a rapid reconstitution of thc black fly population. [t must bc noted t6at thcfailurcs of trcatmcnt may also lead to the same results (rnôrcase on black fly densities). Rcgular supcrvision by {-rcld tcams (captors especially) should enable fluctuation in density that reflects thecfficacy of larviciding to be recorded. Any treatment failure could, thcn, be qulctty detected andaddresscd, since it would be related to a specific cause. The vector to be eliminated in the Itwara focus, and its sub-foci (Siisa and Aswa) is the S.neavei- This species is however, vulnerable, for under the pressure of insecticide treatment, thepopulation decreases very fast. However, a sudden re-infestation is irnprobable because the .S. rteaveipopulattons rcconstitute very slowly (long pre-imago development; phoretrc aspects), and thedcforestation does not favour the displacement of black flies. In addition, since the fo"rr'i. i.olut.à, vector elimination has multiple chances of success in the area. However, the problem of insecurity needlto be addressed, since in certain periods, this impedes or even stops activities. ln view of the current situation, vector elimination activities in the ltwara focus and its sub-foci(Siisa, Aswa) should be successful. It is probable that the children population does not practically haveany microfilaria carriers. However, the distibution of ivermectin must continue, to take into consideration the longeviÿ of adult worïns of the O. volvulus, which might be carried by otae. patients. I 32 4.4. FOCUS OF MPAMBA-NKUSI In Dccembcr 1996, thc project Mpamba-Nkusi was approved as part of the..vectorelimination project in thc ltwara focus". On the recommendation of the Technical èonsultative Committee of theAPOC programme, the said project was re-defined and separated flrom the Itu,ara locus in 199g. TheProjcct was then approved as a feasibility study of the vector elimination project of the Mpamba-Nkusi focus. 4.4.1. I'rcsentation of focus The area concerned by the vector elimination is located in the northem part of the Kibbledistrict. The focus was discovered in 1991 by Adele and Walsh, who, given the proximity of the town ofKibble, called it "Kibble focus". The size of the focus is not lsrown, but it is estimated to be 100 sq Km. the average altitude in the area is between 900 and 1,500 m. A good roads network allows foi easy accessibility of the various points of the focus. The distict of Kibaale has 3 prefectures: Bugangaizi, Buyanga and Buyaga. Only the latter is onchocerciasis endemic; the population at risk is estimated at 70,000. The Buyaga prefecture is dividedinto sub-prefectures. Among these, onchocerciasis is found in Kagadi and (yânaisoke, which are watered by the river Mpamba, at Muhooro on the Nkusi and Ntengo rivers, and at Mabaale on the Mutungulu River. The rainy season is from August to November, and the dry one from December to March. For the rest of the year, the whether is sometimes dry or rainy. In a year of very good rainfall figures, the highest can go up to 1,200 mm. The hydrography of the focus is made up of perennialrivers. They run belou, the forest galleries, but remain accessible. They shelter the S. neavei breeding sites, which are productive all year round. The vector, at the larva stage, lives in phoretic association with crabs of the potamonautic. The zone is characterized by high vegetation. (elephant grass), and forest galleries along u,atercourses. Some forests are practically impenetrable. The area of the focus, previously sparsely populated, has seen the amval of several migrants. The latler come from the densely populated areas of the region to the West Nile (districts of Ara, Moya and Nebbi), and the valleys of Kigezi-Highlands to the southeast (districts of Kabale and Rukungiri) of Uganda. These two areas, the origin of the migrants, shelter onchocercal foci (namely the ioci of Wadelai, West-Niles and the forest focus of Bwindi), u,hich have high prevalence rates (56 to 80%: Nelson, I958; Mc Crae, 1962). The area meant for vector elimination is isolated, in principle, because the nearest focus is 40 Km arvay, a distance which is beyond the flying capacity of the S. neat ei. Besides, ivermectin has been distnbuted in the focus since 1992 by Sight Savers Intcrnational (SSI). 4.4.2. Nature of works No followed-up sun/ey rvas conductcd rn thc Mpamba-Nkusi focus before APOC activrtrcs. IIo\'1'1's1 . sotttc sourtdrngs takcn on tltc vcct()r (rrJcrrtrt1,, supl)orts of 1tr-..-intago stages), and thc Prcvalctlce ol tltc dtseasc (lLaprd lJpidcmrologrcal Asscssnrcnt. IlliA; skrn snrp tests) wcrc carric6 out rp thc 1990s. '[he oblectivcs of thesc rvorks wcre compatrblc u,rth thosc of the feasibilrty study approvc<i by ^l'}O(' to bc implcmenlcd rn thc Mpamba-Nkusr locus. Thc-y arc summeci up as follorvs: ? a33 Determine the identiÿ of the vector; Determine the limits of the reproduction sites of the S. neavei; Specify thc dynamics of the pre-imago and imago populations of the vector; Determine the natural vector charactcristics: infcstation rates, MTp, ABR, transmission indices. Collcct base hydrologic data; they are indispensable to the conduct of treatment; De termine the spraying points, and the frequcncy of treatment of breeding sites; Evaluatc the scnsibiliÿ of larvae to Temephos (dose, efficacious carrying capacity). 4.4.3. Rcsults obtaincd a) Prospecting of brecding sites . From September to December L999,45 breeding sites were prospected on the main rivers(Mplmba, Nyabwegyereka, Rwabutuju, Ntengo, Murungu, Mutunguru and Nkusi). This prospecting enabled the harvest of 688 crabs, of which 284 (41%) carried p.e-irnugo stages of tne S. neavei. Tlte crabs were highly infested on the Mpamba and Rwabutuju rivers, whereas thé load was average on theNyabwegyereka. On the Mutunguru, however, the crab population was very weak, and no S. neavei was harvested on this watercourse. , From January to November 2000, all the rivers of the focus were again prospected to determine the area of distribution of the S. neavei breeding sites. The captures and exÀination of crabs were donein accordance with the techniques of Mc Mahon (1958) and Raybould (1969). The results show that out of 623 crabs captured, 506 (8 t%) were positive, and the average number of larvae of the S. neavei, per crab, was 10. Taking into account a monthly distribution, the lowest load (5 larvae/crab) rvas recorded in June, and the highest (16 larvae/crab) in March. The most infested crabs were found in the Mpamba and Nyabugando rivers. The identification of harvested samples rndicates that the S. neat,ei rvas found everyrvhcre, except on the Nkusi river, where this species rvas replaced by the S. darttttosttLrr, Nkusi t1pe. The preliminary works are in their second year, and activities were essentially based onprospecting of breeding sites, and the choice of spraying points in the dry season. Thus, bemlen January and August 2001,642 crabs, of which 343 (53.4%) were infested, were harvested in the rivers of the focus. The most infested crabs were from the Mpamba River. b) Captures-Dissection-Transmission ln 1999, 399 females were captured between September and December at Sioni, a village located in the valley of the Mpamba River. The 167 parous females dissected revealed 35 (zl%)infectèa and 1(4%) inlective females. From January to November 2000, adult captures were also carried out at Sioni. Out of the 1743 females captured, a number of 524 parous ones were recorded, 126 (24%) infected, 243 (0.6%) infective ones, and 40 Lil1000 parous ones. As for the captures at Rurembo in October and November 2000, they helped to harvest 129 females, including 27 parous ones, l0 (37%) infected ones,2 (7.4%) infective ones and 111 Lil1000 parous ones. Finally, from May to November 2000 1484 females were captured at Nyabudango. The dissection of thesc females revealed 363 parous ones,99 (2i.3%) infected ones, l9(52%) infe ctive one s and 41 Lill ,O0O parous ones. , In 2001, captures \\rere also carried out at threc capture polnts of the focus. Thc ycctor charactcrlstics recorded at Sionr u,cre 33.9%o o[ parous females, 14.1y" ol infectecl ones, 2.79{r of- rtrlccttVc otlcs, a IVI'l'l) of l3 and 50 l-rl1,0()0 parous ones Ar I{urenrbo,26.5o^ olparous lc,ralcs ircrc observed, 20.4% olrnfectcd oncs,0.67u ol'infectivc ones.2l Lrl1,000 parous ones, and a M'll, cquaI to 28 was noted. Frnally, at Nyabugando, the resulls of transmission were 2l .B%of parous fcn-ralcs, lg.3% of infectcd parous ones,3.57o o[rnfectrvc ones,6l Lii 1000 parous ones, and a MTp equal to g6.Zyo. ? 34 c) Larviciding An expcrimcntal treatment session was conducted on thc Mpamba Rivcr in November 2000. 'l-his trcatment was preceded by prc-treatment data collection on the crabs, breeding sites of t6e .S. dutnnosturt s./, the water of the river (pl{, temperature, conductivity) and the fiow rate of the watcrcourse. Thc results of insecticide treatment indicate a reduction in infestation of crabs of the river,going from 66.7%to92-5%o. The same goes for the crabs enclosed in experimental cages placed in thc riverbcd, where thereduction rate fluctuates between 98.5% and 100%. As for the supports that shelter the S. darunosum s.l. or other Simulidae, they wcre all 100% negative, through the insecticide rvave. I{owever, the non-target fauna (trichoptera, leeches, water bcetles) was not affected. During the expcriment, the flow rate of the Mpamba river was 1, [ 26 m3/s, the water tcniperature was I9.2oC] and thc carrying capacity of the insectrcide estimated at 5 Km. The objective of the experiment conducted in July 2001 was to determine the effective carrying capacity of Temephos in the dry season. The Mushandikwa and Rwabutuji rivers rvere selected foi thË tests. Cages, containing 4 to 7 crabs bearing pre-imago stages of the .S. neavei, were placed in the rivers. The latter were treated with 300 ml (Mushandikwa) and 500 m, Rwabutuji) of Temephos. The post- treatment conhols, conducted 48 hours after spraying, revealed that the effective carrying capàcity(100% of mortaliÿ of larvae) of the Temephos was about 2 Km, for flow rates that could not be measured, since they were too low. d) Onchocerciasis prevalence Onchocerciasis is endemic in the Mpamba-Nkusi focus. Nelson (1958) and Mc Crae (1962) put the prevalence between 56' and 80%. In the valley of the Mpamba River, an epidemiological survey conducted at Nabwereba revealed 92%, ol oncho patients in the community (Ayele and Walsh, l99l). Prurit is recognized as being one of the most severe clinical manifestations oIonchocerciasis. ln 1995, the REA survey brought to the fore that the prevalence of nodules varied between 46% and 53oÂ. Except that in the region of Kagadr, the most affected villages were Nl,abrvereba (53%) and Soni (60%), whereas in the Kyanaisoke region, 46.7% and 30% of carriers of nodules were counted at Kanyabeebe and Mpamba respectively. c) Isolation of Focus The Mpamba-Nkusi focus has simtlar aspects (geographical, ecological) u'ith the sub-focus of Siisa rn the Babarole district. The preliminary data indrcate that the said focus is ecologically and geographically isolated. In effect, the S. neavei species rs practrcally the sole vector of the focus, for the S. damnosunr s.l. found are essentially ornithophilae (colbourne and Crosskey, 1965). Besides, the focus of Bugoma in the north is extinct (Walsh et al, 1996). [n the east, the Mutungulu Rrver only shelters a small quantiÿ of crabs, hence the absence of the S. ncavei. Frnally, the ecological conditions are such lhat no re-invasion can come from the east or south, except the u,est, where prospecting should enable the limits of the focus to be determined. 0 Training The implementation ol a control prograrnme, as planncd in the Mpamba-Nkusi focus, Irecessitates quahfied staff (high-level, technrcran and captors). The trarning of local staff on all technical attd practtcal aspects of cntomological evaluatton is ol utmost ncccssrty. Cer1arnl1,, an entomologist and lbur captors arc already opcrational, but thrs rs tnsufficrcnl to cover the entire locus. Personnel of the ltrvara locus (corn;retcnt and cxpericnced) could qrvc tcchnrcal strltport to tliat of N,lpantba Nkusi 4.4.4. CDTI status in Focus 1'he Mpartrba Nkusr focus is located rn tlte Krltaale clrstrrct. Thc total population ol thc crrdentic zonc ls 112,884 pcrgorls, wlttch is dtslrtbutcd ovcr 154 conrr.nurrrtrcs, ol rvhrch 136 are rn arr onchi_r 35 hyper-endemic zone, and 18 in a meso-endemic area. Mass treatment with ivermectin started in 1992, Ylllh" SSI campaigns. From 1994, I I1,154 persons were treated with ivermectin. I must be noted thaiCDTI was adopted in 1999, and the first distribution was completed in August of the same year, i.e. onc month before the start-up of the "vector elrmination" project. In 2000, the thcrapeutic coverage rate was 65% (63,841/98,816). This rate is74%o (832991112884) in 2001. The 4'r' phasc of CDTI in Uganda covers thc Mpamba Nkusi focus, and it is the second consccutive year that treatment is being financcd by APOC. Of course, the target population of thedistrict is known, but it is equally indispensable to determine that of the focus. tt,is precision would make it possible to monitor the progress of therapeutic coverage in the focus, and to r.s".. the impact ofivermectin on oncho transmission. 4.4.5. Budgct for vector elimination Activities To enable vector elimination activities to begin and continue, the APOC programme provided regular financial assistance, on the basis of letters of agreement (Contracts). fne LUt-e below sums up the financial component of the project. Covered pcriod Cash transferred to field (in US$) Amount spent (in us$) Purchase of equipment Total cost May.99-Dec 00 46,051 30,664 60,240 90,904 Jan.0l-Dec 0l 15,3397 NA 17,560 r7,560 Total 167,910 30,664 77,800 l!§r464 4.4.6. Discussions-Remarks _ The various prospecting activities undertaken in the Mpamba-Nkusi focus agree on the identiry of the vector causing onchocerciasis, namely the S. neavei. This species, given the ivorks conducted in 2000, is present all year round in the breeding sites of the focus. Its pre-imago population is the least abundant on the crabs between May and August. Of course the S. datnnorurr, thr- Nkusi ÿpe, is foundin the breeding sites of the Nkusi River, but the species is not anthropophilous (Colbourne and Crosskey, 1965).Theabundanceanddistributionofthepre-imagostagesofthes. neaveihelptodirectlarvciding, preferably toward the Mpamba and Rwabutuju rivers, which shelter the most infestàd crabs. The results of captures and dissection carried out between September 1999 and November 2000 show that in the Mpamba-Nkusi, the S. neavei is a good vector of onchocerciasis. [n effect, the number of infective females per 1000 parous females varies from 42 (Sioni) to 74 (Rurembo), while the tolerable line in the OCP area is one infective female per 1000 parous ones. The same goes for the number of infecting larvae per 1000 parous ones, which fluctuate between 40 and l l l, wheàas the acceptable limit is l0 Lil1000 parous ones. The vector characteristics (MTP; Nb Lii 1000 parous) recorded in 2001, are equivalent (even higher) than those observed in 2000. This means that the nsk is real for human populatrons living in contact with the S. neavei in thc Mpamba-Nliusi focus. Of course, the phoretic association with crabs limits the reproductron of black flres (number of bites/man/day, generaliy lower than 30). The fact sttll remains that these low densities are capable of causing inténse transmission. Transmission remarns high, despite the distribution of ivermectin. It must be saiJ that this phenomenon, observcd equally at Kicheche (district of Kabarole), was reported by several authors. The latter are unanlnlous in assertrng that ivermecttn does not intemrpt transmission, but partialll,. 'l'hc cxpcrrntctrtal trcatmcnt, whrch u'as car|rcd out on the i\41tantba l.\kusr Rrver rn 2000, brouglrt about a drastrc reductton in the rnfestatron (66.7%-100%,) of c.aÙs. It rvas the sarne lor 200 I, whe n thc treatnlcnt of the Mushankikrva and Rrvabutu-; r rivers causetl 100% of mortaliry of larvae o'er 2 Knl. Thrs result corroborates the observatron made in othcr foci (ltrvara, Sirsa, Asa), and indicates that tlrc Tcrncllhtls is the selcctcd larvicidc for ground trealrrent oIbrccclrng srtcs rvrt6 S t,rca,r,ei . Its cl'ficac' 36 and active carrying capaciÿ help to clean up the breeding sites after some treatment cycles. What remains to bc addressed is thc problem of dosage, in relation to the gow rate, and tlte number of spraying points. 4.4.7. Conclusio ns-Suggestio ns Thc expericnce gained by OCP in the arca of recording o[ entomological results, helped this institution to finalize excellent data collection forms. It is therefore preferable to use these forms, for thcy better report captures, identification, dissection and black fly infestation. These forms enable each person to verify and interpret results. The identification of samples that are harvested indicate that the black flies found in the Mpamba Nkusi focus are of the S. neavei and S. danutosutrt, Nkusi type. The latter, though classified as non-anthropophilous, needs to be better characterized, and its vector status well defrned. The kaining of local staff, which will guarantee the continuiÿ and efficacy of control activities, is of utmost necessiÿ. Staff will have to be tained on all technical and practical aspects of treatment with insecticides). The personnel of the ltwara focus, which is competent and experienced, could technically assist the Mpamba Nkusi staff. The biology of the.S. neavei, the success of the experimental larviciding, the extent of the focus, the geographical and ecological isolation of the focus, and the accessibiliÿ of the rivers in all seasons, are some elements that indicate that the elimination of the vector in the Mpamba-Nkusi focus could be undertaken with success. The problem that remains to be solvèd is that of insecurity, which, at any time, may impede the conduct of vector control activities. Despite the efficacy of larviciding, and the probable elimination of the vector from the Mpamba Nkusi focus, the dislribution of ivermectin will have to continue, to take into consideration the longevity of adult worm oIthe O. volvulus that are found in former patients. a I37 5. OVERALL CONCLUSTON 'fhis sums up the points pertaining to the training of localstaff of projccts, supervision of activities, andthc atLainmcnt of thc final objective of the various vector elimination projccts: - Thc expericnce acquired by OCP indicates that the implementation of a control programme, asplanned in the Tukuyu, Bioko, Iwara and Mpamba-Nkusi foci, calls for qualiiieipe.so.rnel. Enhancing training of this personnel is indispensable (especialty at Biokoi. Given the actual training needs in all the countries, measures need to be taken, not only in thé countries (namety the objective selection of candidates), but also in APOC (organizing training). - l-hc efficacy of vector elimination operations is lrnked to the continurty ip àctor control actions.fhe lattcr is evaluated, thanks to entomological surveillance. Thc OCF experience indicates that the supervision of activities remains the key to success, for it ensures quals in data collection. - It is' therefore, desirable that measures are taken to ensure supervision of activities (essentially entomological surveillance) conducted under the various vector elimination projecs. ThL coordinators of projects and APOC must play prominent roles. - The longevity (10-15 years) of adult O. volvulus worïns is such that the distibution ofivermectin will have to continue in all foci for at least l0 years. Even in foci where elimination activities are successful, distribution of ivermectin must côntinue, due to th. p."r".,"e of formerpatients (carriers of nodules). - The reports on the elimination of the vector in the different foci in Tanzania, Equatorial Guinea and Uganda, were an opportunity to assess the state of progress of eactr project. It clearly appears that the projects were undertaken on the basis of elements, such as the siie of the focus,its isolation, base data available, and the cost, as compared to CDTI. The only thing is that thepractical feasibiliÿ of projects was not sufficiently taken into account, and some faclors (actual limit of focus, accessibiliry of breeding site, risk of rc-invasion) were, at times, underestimated. Of course, when the vector is S. neavei,the factors mentroned above are *o." o, less attenuated,just by the mere fact of thc bio-ecology of the vector. On the other hand, rvith the S. dantrtosurrt s.1., the limiting factors become numerous: abundant supports, difficult accessibility to all breeding sites, black fly densities, which are generally high, high flying capacity. Ani yet a- 100% coverage of breeding sites is an imperative condition for vectôr elimination. Besiàes, it was agreed that in the selected foci, the elimination of the vector would be complete, definite and fast. This objective remains achievable for the foci of Itwara and Mpamba Nkusi. On the contrary, the reality on the field makes it mandatory to recognize that vector elimination at Tukuyu and Bioko risks having an objective that is too ambitious. It is rvorth recalling here one of the recommendations of the JAF6: if the meeting decides that vector elimination activities must cease in the focus, recommendations will need to be made to the country concemed, so as to enable it continue vector control in a national or brlateral context (cooperation). On the other hand, in the event rvhere activities will have to be continued, practical Àeasures must be taken by APOC for implementation, supervision and evaluation of treatment activities_ 38 6. AKNOWLEDGEMENT We arc pleased to thank here all thosc who in any manner enablcd tl-re preparation the current synthcsis on the onchoccrciasis vectors elimination activitrcs in somc foci of Cential Africa (Bioko inEquatorial Cuinea) and the East (ltwara and Mpamba-Nkusi in Uganda, Tukuyu in Tanza.ia). We would like to thank particularly : - Doctor A. SEKETELI, Director of the APOC Programme, for his trust on me bygiving me the analysis and update of the data of all kinds which are pertinent to decide on the possibilities and conditions of vectors elimination. I{ii experiencc and knorvledge o[ the various foct rvere vcry uscful to us in thc preparation of this document. Doctor M. NOMA who, with his remarkable knowledge of the foci and his availabiliÿ gave remarkable and efficient help. - Our work was carried out thanks to the assistance of many peoples (administrative and finance officers, secretaries, drivers) whose competence,, dlmamism and faithfulness are appreciated. ^ 39 7. 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Wilson, M.D., (1999) -WhoiAfrican Programme for onchocerciasis Control Onchocerciasis vector elimination project (Bioko, Guinea Equatorial): Progress report. Wilson, M.D.,Cheke, R.A., Mas, J., Mc Call, P.J., Post, R.J. & Sima, 4., (1996) - Evaluation of the potential eradication of onchocerciasis from the Island of Bioko, Republic of Equatorial Guinea. (Who/TDR Project no. 050/181/34, Id 950612). Final report and supplcment. Unpublished report for Wto/TDR, Geneva. Wilson, M.D., Mafuyai, H.B. & Post, R.J., (1994) - Morphological Identification of sibling species of the Srmulium damnosum complex (Diptera: Simuliidae) from Nrgeria, Cameroun and Bioko. Proc. Exper. & Appl. Entontol., N.E.V. Atnsterdaru 5, I Bl-185. Woodruff, A.W., (1965) - The distribution of onchocerctasis [n Tanzania. ll/ho miuteographcd docuntent Wo/Oncho/32, 65. pp.3. Yaméogo, L., (2000) - Commentaires sur documents d'EIE sur I'rle de Bioko. 348/00/|/CU/ADM/6.1 a 43 a ANNNEXES: TABLES AND FIGURES 44 Table 1 : Captures and dissections at Lufilyo crater (TUKUYU - year 1g9g) Table 2 : Gaptures & dissections at Lwangwa masako (TUKUYU - Year lggg) MBR Morilhs Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 4 4 4 4 4 4 4 4 4 4 4 4 48 Captured 175 74 46 13 3 19 B4 22 a 7 12 35 499 Dissected 174 74 45 13 3 19 84 22 I 7 12 35 497 Parous 53 13 14 5 1 5 21 I 2 2 3 18 145 lnfected 16 3 3 0 1 0 0 1 0 0 0 0 24 lnfectious 0 0 0 0 0 0 0 0 0 0 0 0 0 Nb de L1 0 0 0 0 0 0 0 0 0 0 0 0 0 MBR 1 305 555 345 98 23 143 630 165 68 53 90 263 MTP 0 0 0 00 0 0 0 0 0 0 0 0 I Months Total Jan Feb March April May June July Aug Sept Oct Nov Dec Nb of days 4 4 4 4 4 À+ 4 4 4 4 4 4 4B Captured 1 0 0 1 J 112 222 201 62 7 26 0 635 Dissected 1 0 0 1 3 110 222 201 62 7 zo 0 633 Parous 0 0 0 1 1 19 63 B4 5 2 6 0 1Bl lnfected 0 0 0 0 0 2 5 4 2 0 0 0 13 lnfectious 0 0 0 0 0 2 0 1 0 0 0 0 3 Nb de Ll 0 0 0 0 0 3 0 B 0 0 0 0 11 B 0 0 B 23 840 1 665 0 1 s07 465 53 195 0 00 0 0 0 0 60 0 0 tl B3MTP 45 Table 3 . Captures & dissections at Tapio bridge (TUKUYU - year 1999) Table 4 : captures & dissections at Kambasegela (TUKUyu _ year 19gg) Months Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 2 2 2 2 2 2 2 2 2 2 2 2 24 Captured a 18 43 11 1 0 6 1 19 I 4 35 2 149 Dissected 1B 42 11 1 0 6 1 19 I 4 35 2 148 Parous 6 15 6 0 0 2 0 6 1 2 2 0 40 lnfected 0 1 0 0 0 0 0 0 0 0 0 0 1 lnfectious 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 lt Nb de L1 270 645 165 15 0 90 15 285 135 60 525 30 MTP 0 0 0 0 0 0 0 0 0 0 0 0 0 Months Jan Feb March April May June July Aug Sept Oct Nov Dec Total 2 2 2 2 2 2 2 2 2 2 2 2 24Nb of days( tured 1 2 0 J 0 3 6 14 3 0 25 22 79 Dissected 1 2 0 3 0 3 6 13 3 0 25 22 78 Parous 0 0 0 0 0 1 0 7 0 0 5 11 24 lnfected 0 0 0 0 0 0 0 1 0 0 0 1 2 lnfectious 0 0 0 0 0 0 0 0 0 0 0 0 0 Nb de L1 0 0 0 0 0 0 0 0 0 0 0 0 0 MBR 15 30 0 45 0 45 90 210 45 0 375 330 0 0 0 0 0 0 0 0 0 0 0MTP 0 0 Monlhs Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 4 4 4 4 4 4 4 4 4 4 4 4 48 Captured 24 72 220 281 228 409 328 228 202 182 13 43 2230 Dissected 24 72 220 277 227 407 326 228 200 180 13 43 2217 Parous I 15 56 95 61 126 113 140 50 16 2 18 701 lnfected 1 1 4 18 14 15 o 20 6 4 0 7 99 lnfectious 0 0 0 00 1 1 6 0 0 0 1 I Nb de Ll 0 0 0 0 0 1 5 13 0 0 0 2 21 MBR 180 540 1665 2108 17 10 3068 1 809 1710 1515 1365 98 323 PMT 0 0 0 0 0 8 28 98 0 0 0 15 149 46 Table 5 : captures & dissections AT Lufilyo crater (TUKUyu - year 2oo0) Table 6 Captures & dissections AT 2o0o) Lwanga-Masako (TUKUYU - year I Months Total Jan Feb March April May June July Aug Sept Oct Nov Dec Nb of days 4 4 4 4 4 4 4 4 4 4 4 4 4B Captured 1 1 3 36 198 470 405 524 79 90 7 1 181s Dissected 1 1 3 36 193 456 402 440 79 90 7 1 1 709 Parous 1 0 2 6 51 165 139 1 5 1 4 5 0 0 s24 lnfected 0 0 0 0 1 5 oU 2 0 0 0 0 16 lnfectious 0 0 0 0 0 1 2 1 0 0 0 0 4 Nb de L1 0 0 0 0 0 4 6 4 0 0 0 0 14 MBR MTP B 0 oU 23 270 1 485 3525 3038 3930 593 675 53 B 0 0 0 0 31 45 Jb 0 0 0 0 112 47 Table 7 : captures & dissections at rapio bridge (TUKUyu _ year 2000) Table 8 : captures and dissections at Kambasegera (TUKUyu - year 2o0o) Months Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 2 2 2 2 2 2 2 2 2 2 2 2 24 Captured 129 1 6 1 81 31 43 258 607 81 144 220 95 43 1893 issected 129 160 81 30 42 258 311 BO 143 159 95 43 1 531 Parous 49 53 19 12 10 71 115 51 47 21 6 o 463 lnfected 0 3 1 0 3 6 I 1 1 1 0 0 24 lnfectious 0 0 0 0 0 1 0 1 1 1 0 0 4 Nb de Ll 0 0 0 0 0 3 0 6 4 10 0 0 23 It 1935 3415 1230 465 645 3870 9105 1215 2160 3300 1425 645 MTP 0 0 0 0 0 45 0 15 60 207 0 0 327 Months Jan Feb March April May June July Aug Sept Oct Nov Dec Total Nb of days 2 2 2 2 2 2 2 2 2 2 2 2 24 4 32 36 o 2 14 28 113 20 22 3 17 300 Captured I sected 4 32 36 I 2 14 28 113 20 22 J 17 299 Parous 0 5 5 0 1 7 B 33 4 6 1 7 77 lnfected 0 0 0 0 0 0 0 0 1 2 0 2 5 lnfectious 0 0 0 0 0 0 0 0 1 0 0 0 1 Nb de L1 0 0 0 0 0 0 0 0 I 0 0 0 I MBR 30 480 540 135 30 210 420 1 695 300 330 45 255 MTP 0 0 0 0 0 0 0 0 135 0 0 0 135 48 Table 9 : Captures and dissections at Bioko (april-may 2OOO) Table 10: Captures and dissections at Bioko (february 2001) Balacha de Riaba Barleycorn Musola Sampaka April May April May April May April May Nb of days 3 5 2 5 4 4 3 5 Captured 419 839 765 1717 345 182 331 540 Dissected 316 464 334 517 345 182 264 468 Parous 115 184 141 199 147 61 140 228 lnfected 5 5 13 4 18 7 15 18 lnfectious 2 1 2 2 I 3 2 5 Nb de Ll I 1 5 5 36 27 5 38 MBR 4190 5034 11475 10302 2586 1 365 3310 3240 MTP 119 11 172 99 6 270 203 63 263 Nb of days Captured Dissected Parous Parous infected Parous with L3 NbLi MBR MTP Sampaka I 222 106 49 25 3,8 5 56s5 319 1 't55 B9 23,6 19 9,5 6 Barleycorn 1 213 65 32,3 19 19 9 61 35 349 1 196 93 409 5,3 0 0 Musola Village 1 282 BO 48,7 179 7,7 35 9490 1275 1 340 96 61.4 22 1,7 1 1 327 92 46,7 25,6 0 0 Balacha da Riaba 1 118 69 33,3 8,7 0 0 351 0 1 116 B6 39,5 1 1,8 0 0 Riaba 1 359 65 26,1 0 0 0 I 038 0 72 1 333 BO 36,2 10,3 6,9 1 Granja da Musola River Musola 1 209 BO 30 8,3 0 0 4185 655 1 70 B6 64 14,6 7,3 26 Granja da Musola River Eba 1 149 60 43,3 11,5 0 0 4470 0 River Eba on road to Moka 1 123 80 32,5 19,2 0 0 2970 19 1 75 72 44,4 12,5 6,2 1 Moka at river Chuba Total tl 3293 5 1 304 60 0 0 0 84 300 0 268917 1 49 Tablell: Captures of simulies before and during vector control campaign BUSASA KIJURA Months 1994 1 995 1 996 January 312 827 0 February 262 333 0 March 484 720 3 April 672 9'19 2 May 624 450 0 June 500 430 1 July 260 187 Auq 449 1B 0 September 373 4 0 October 337 12 November 344 3 december 36s 1 Total 4982 3904 6 soGoHt Months 1994 1 995 1 996 January 96 19 0 February qq 7 0 March ÀaalLO 6 0 April 348 1 0 May 396 2 0 June 311 24 0 lqtv 123 J 0 Aqs 312 1 0 September 151 0 0 October 14 0 0 November 23 1 0 december B9 0 0 Total 2390 64 0 1994 1 995 974 743 0 632 s14 0 786 266 0 292 250 0 606 315 0 652 277 0 193 159 0 325 11 0 748 1 0 431 I 0 283 1 0 481 0 0 6403 2546 0 SIISA 199s 1996 148 428 1 187 387 16 740 316 0 111 .JJ ' 111 16 360 149 2 571 751 q 121 391 tl 217 303 2 104 10 1 72 4 0 44 2 0 26 J 0 2927 2855 49 1996 1994 50 Fiq.1 Tukuyu Onchocerciasis focus: Altitude range, dry season, S. damnosum larval habitats I,lt:.;fiùTU fit:i.i: i1r. Filt'triilf .Ô' AT"o"'! ti,?v /, qi':. : r ç,") A 't tn!' ,J i, 1û 15 20r"H J :3 v4 'rJ^ ,...1 ir. I Fiq.2: S. damnosum monthly biting rates (MBR) at four catching points in relation to monthly rainfall in Tukuyu focus, October 1998 to September 1999 lS:r'l lÈn:' l.{00 I ii:r.'l lrvJ) I tû0 ùx .r{}l lri{.r r € ; _1 d Uti È6 {I .-,1 I I ___ l Ehy.t\lÂr r I -Ô l-'Ynjr:t<IJl + ll-tflt1) :r - K:\_i:,:t.:1 1 t.1 'h-58 ,t{-!d (r:(-!€ f-r.ÿl FÉàee p5rÿl .Arr.ÿl ,.i}ï,1.3 l'l:flttÉ. 'r)1 1? lrl ,y; r,r}jt,ii, ,ira.]i i r_,H _ty U Y aÂLl St .E,ÿ I''IALAU I (]vÉ.r Ilald el t-.1'. Lrr{: 5.Û i0f '-= I 5l t: )u::a j7: r'. Iü, rv,{-e(a!":lnts s lt'P Cts\I!, t.l'É iEscs: Fcrs;u al -i:ïJ:À!leg àr-Ê -'€.lrk€tj.[.§,k( l{r{rû j.3 ]:"'1?f L . ,'l'lla f,æa'È ,r à-l -,t.\ l4uùl LEGEIIS: a 3 l:r.d1-nE :i:.crs Ci!rotcl gi-.--r: s tnt- icn I-lt'â:,aLer-rl :r I =L: : :f,.r .T I I I I \ I à 4 I .2 ? Li n "l5 51 Fiq.3: S. damnosum monthly biting rates (MBR) at four catching points in relation to monthly rainfall in Tukuyu focus, October 1999 to September 2000 ruxto 9000 8ffi 7ü,0 6000 5û00 40m lso 2000 l{rrl 0 I 1 I B § 6 E 5 I I I -,--l 0d-9'!) rtr-99 Oæ-91 ,bn-t» Fc§[O Ètür.00 Al7 oil t4T'm lùn rJ.l il--,]t, À,.IJ-l:r-r 5etrlr;l l,tcrÊJr. r:t I 1_i l 'snquafârr l ' -- vUrscxf-ll I r L'.Jrn rô I *--^rr) i +V!bC-+.t^] 350 lm Fiq.4: S. damnosum monthly biting rates (MBR) at Kambasegela catching point in relation to monthly rainfall in Tukuyu focus, October 1999 to September 2000 I.U I l1r. I I{: lltt l,!t E 250 ë{mo Ég ü 15û § IË roodà5 §so E R $rÀAll l---I- tr'tsR -I- ri 0 ftl-99 lùv-s0 Dn('99 Èn'00 Feb00 l'§r{o Apr-!û r4lv-fil .)-n-ül Jul-lrl Ar9 0'0 56'C0 / i' Hor{ltr I I Il E fig 5: 52 Annual rainfall in Tukuyu Focus, South West Tanzania Source: Chivanje Tea Estates Ltd: 1980-2000 w l$o sl0 15,''1 .F .L:tto J ! rr.t I lùïl S.10 Ë, .:iq: Fig 6 : Simulium damnosum s.l. breeding sites limits, dry season, 2000 ,t\ s1 -o-' ^-d .:d' {r- s' d' +d r*C d +*.*S rC -*".a,?'.,e,É' t,ûth{IÀl}{i \ Fp0R I I I "r+;, ,,I II I l-- +or. "4/\- - - '4rrn: l,:! --* hiY Àt, tt I ( I l(rn ;tI __l I I I I I I I I tI I I I I I I I I il I 53 !!g,Z : Capture mensuelle sur les rivières Lufilyo, Kiwira et Mbaka (Tukuyu) 1200 r000 - a- KIWIRA -#Mb*e - -Lutïp 4 /1 I1/1 I1 I1/1 I1 !lo tIl,*tt Ê E .00 /\\ \ saêpEtnrri 2&(.6rs / \, tJ/" I \ \ / r'\ WEEK 01 \\ \./\ \ .2" \ /-- \.200 0 Tukuyu focus vector elimination project Insecticide dosing points AINS ffi. RLrr.lS\,iË' ) o jrru41 FEV H F§ AVRIL hlAl JUIN JUIL AOUr SEPT OCT HOV OEC irffid2 Fis.8 r =r 3 /"1PoR01 L JJ krY r-u 4d: li,tÏ.tÊ Êla llte 5 BuJaNfà Êe -- ae - ne+tJFfrFgi Ir. L., !zê= K.it^ LÔâilf,, f'r L' ,ïô = nqrrP46e RV l-' 1êû : nulltl'tJüfÊa À.p; gp : trÇog_o Êv_ ri ?Èr r lJi èm§t Rv tt9 iæ = krfrair6E Êu :u 1@ = krl.E64 eu.ù 1rù j n gutr 4,. I - - "r ?'l5S .......,i Bord€r ('tr.[ltr ÂiClfcula a Bi Clrcüia B qi(:ircùti C a)?l:arrotqd t,TrÊrled IGY - e;- 05t: ,. ) l'.i \ \ D !. Fiq.9 Fiq.10 54 Tukuyu Focus vector elimination proiect lnsecticide dosing points HOUNTAINS MT. RUN6\üE .,' WEEK 02 to 06 kÊY fu4ars ÿlftE â* l$ re = 8Lr+Jb Rr. ru 6o ' rltttllhFrÊ suL!7@: krÊ{t{ânâxg ft 14, too = Fl!urxû(&.r^ Êu[r lor : nltrlr{-tJdgE'rr Ê! t<r So: NCqS Êÿ. kT 1ü . luYÂnltf ev ,Yf 5ôo = kt(,trr{È.Rv,Lu ls r khue{ Êu.w î1@: HgUlJ Rt. !- .: =E ! M n (é _,_,- e.t5.!. ç t I ',--..-,. Bordrr Clrtult{ AtCirs!il,A-. gl Ctrcr( I (1. Circull C Ç l-lnlrcrte* ' J O : TretcaY ___ _ 1"r5' j t_,: A\{l ..:.,r ,----,lcL. 05 Tukuyu vector elimination proiect Prospection map Hï. RUr,r6V/E POROl Y{EE(01 __- - KEL 0 id: iîftE R\t i!'IÉ ' BuiNiD q!. ru 6F' -r^!JrylÈÊ. t L, Ta : klPÀ^,${mM e l-, 9s. = IiHzrPÀ6aU Ê L! 9É! : i1BLt,-|,ltsËH k: ID : Nûo;b Ru r q@ = iiyênsl Rr ,!i s+ = i«êeriét çvLv iq, : (trLE6+ Ê,r! .1È: :âL.]l, â1 V)l-I 5 !' è = .,.) Â1 ri Cirsuli A Cirrüll B Bo.dcr Clraùltr ':Ç C, Cirsull C - , Poriti!'e S{tt§ r ! NtBatiÿc §it€t t'I ,t_.\t ( l\ - n[, -r> ed,itrx"Èr.rrüi mfi.&ù ..Él0 lS l0 (ao ttsrora*Èr{f' -l i'15 D a kEY 'r. i -- Rird ( æ P*l-qrv" SÊ.,Eni :mtu{r0À ts-......-..+o s to ts lbxa O hraoox m.,,* Airr , ,!t Fis.11 Fie.12 55 Tukuyu Focus vector elimination project Prospection map ,t'1PoR Sr WEEK 02 !o 04 kEY L r*s ttEL8 Êv p 5æ " 6rrAV!6 Rv. Lu é@ , iw*(LIâAFr a r ù T§ = ktR^ ilüârsno Pr L.r Eæ = llur{r,Êa5^g ç irJ îtu -- n$A[r,J-ü{cÈ!. i,ü tæ: ÏuieE Rv. aÎ tJ = lÿYêrlrft Êÿll8 }oo = h&4il6Ë ÊvLu 1æ = l(À{16+ Êv.u lrôo = È1&(U ft. I MÏ. EUNGWE .,v1 FE 5 E = 1 I @ t!F Ç ,,...., i ÛôrdfiClrculs ef cttcor ,1 sf circut tl ci ctr(ult C -i Poslrh'cslric - ; NeSstiva Slln e'Jc 5 t a. KEY 0 t r0 r5 ?0,(n \_- ! rui -1, A\{rHA - Pif, :-.t Êal"iatænSrrrun WEEK 05 to 06 ,. t.. ' ,',,, L: -kÊ Y Lu +*,= lilttÈ Pÿ, t!,-ê = SLjJ4{§ü Êh!, éæ : i-i 4[srl(lÊfr I r. fd-- krPatl{tÂnÀtr, P L æô: i]Ar)fAÉaU tr l{r ,.r : l:utl')4-/û9&'a !f, gco . lvÉ?J-§ pv ^3 (7'i . t-,YÊnrJt R!ÿ t'o = kl6A,tlrs Fr. L" rS'I I .É' Tukuyu Focus vector elimination project Prospection map HÏ. (ô n POROl I V) FE 5)ÿ = Lu ts: kuLÈC^ t a ...,.,. : 8ôrdtr Clrcqllr {:CircÙit r\ rtl Circvlr I C: Cir.ull C : - : Polrtirù sitÈs -:NrgrtircSitcs c'i; 4 Ç) IGY JtÉ9fl'ta&i 05 r0 15 l0 Ko ,: MAIAWI '"t. 56 Fis.13 : Monthly rainfall (mm) at Malabo in 1991-95 & January-June 1996 Jen FËb liar AD.ll May Junê July Aug MONTH OF YEAR Sept Oct Nov Dec Fie.14 : 700 000 F00g J lloo 2 E*o J F P.oo t00 +t8rt +1992 +1903 +1914 +10e6 - o- 1906 0 Bioko Island ri,, ... f," i l I I B t , a i',: ) I ri' 57 tr'ie.l5 : Monthly biting rates (MBRs) at the River Sampaca in1992 8000 70oo 6000t!( EBooo(, zÊ Elooo à Êsooozo =2000 1000 0 &1É-: Monthly biting rates (MBRs) at the River Timbabe in 1992 lu)00 3500 Jan Feb MalApril Msy June July Aug Sept Ocl Nov Dec MONTH OF YEAR May June July Aug MONTH OF YEAR I ! I 3000 u,l Izeoo2 82000 a{!eB 16100 1000 600 t zg 0 Jan Fcb illar April Sêpl Oct ilov Dec I r [Bâr F 58 Fie.17 Onchocerciasis foci in Kabarole district B sffimFÉs : ? First treatmentÊ of the Sogohi river p ..,,., 8tref d(.ôq@a.M zAl'nE !:.29 Fiq.18 : Number of ,Sinulium neavei caught per day (1994 to 1996) at four catching sites t 1an = ruu =eo (dü rÂno ,r" û O ,^ = o -. ?a) VY V xt I lll v vll ix xi I I;l Months January 1994 to December 1996 ilvvll lx V VII IX X; Catching site: -.-e- Busega a Kijura '- Sogohi r I ____t -æ I, ! ....' a I t