Vector control unit (VCU): progress report, May-October 1983

WORLD HEALTH ORGANIZATION AFRICAN REGION EXPERT ADVISORY COMMITTEE Fifth session Geneva L9-22 June 1984 ORCANISATION MONDIALE DE LA SANTE REGION DE L'AFRIQUE OCP/EAC5 .5 ORIGINAL: FRENCH ONCHOCI]RCIASIS CONTROL PROGRAMME IN TTIE VOLTA RTVER BASIN AREA PROCRAMI'IE DE LUTTE CONTRE L'ONCIIOCERCOSE DANS LA REGION DU DASSIN DD LA VOLTA VECTOR CONTROL IINIT (VCU) Progress Report (May-October 1983) WORLD HEALTH ORGANIZATION AFRICAN REGION ORGANISATION MONDIALE DE LA SANTE REGION DE L'AFRIQT'JE oCp/No .121lvcul84 ORIGINAL: FRENCH ONCHOCERCTASIS CONTROL PROCRAMME IN THE VOLTA RTVER BASIN AREA PROCRAMME DE LUTTE CONTRE L'ONCHOCERCOSE DANS LA REGION DU BASSIN DE LA VOLTA ONCHOCERCIASIS CONTROL PROGRA}'IME IN THE VOLTA RIVER BASIN (ocP) VecEor Control Unit (VCU) Progress Report (May-October 1983) The issue of this document docs not constitute formal publication. lt should not be reviewed, abstracted or quoted without the aoreement of the World Health Organization. Authors alone are responsible for views expressed in signed articles. Ce document ne constituc pas urre puUicrtion. ll ne doit faire l'objet d'aucun comgte rmdu or.t r6sum6 ni d'aucune citation sans l'artoriretbn de l'Organisation mondiale de la Santd. Les opinions exprimdes dans les articles s'rgn{s n'ang4cnt que leurs auteurs. 2OCP/No -121 lvcu /84 page 2 CONTENTS 1. General Characteristics of the 1983 rainy season 2.1 Movements of the ITF .. 2.2 RainfaIl 3. Hydrological characteristics and vector habitat situation 4. Strat.egy and tactics of treaEment operations Aerial fleet deployment Larvicides utilized ... Int.entional interruptions of Larviciding from the ground aerial treatment in the rainy season Monitoring of larval habitats I'lonitoring of biting populations General Biting btackfry o.;;i;i;; 6.2.1 Black Volta basin Phase II river bas:-ns Oti-Pendjari basins Comoti and L6raba basins ..... White Bandama basin Lower Band:ma and Nzi basins Red Bandama basin (Marahou6) Sassandra basin ... Niger basin 0 River basins of the 6 .3 Reinvas ions 7. Evaluation of onchocerciasis transmrssron The initial Programe zone Reinvasion zones Forest zones The southern extension zone 8. The campaign on the Bandiagara Plateau (Mali) 9. Operational and applied research Screening of new larvicides Lleasurement of susceptibility to inseccicides .... Vector role of species of the S. damnosum complex Studi-es on che reduced catching and trapping network Studies on dispersion .. LarvaI life-span studies ... . Evaluation and testing of B.t Adulticide trial Mapping studies 5 6 4.1 4.2 4.3 4.4 7.1 7.2 7.3 7 .4 6.1 6.2 6.2.2 6.2.3 6.2.4 6.2.5 6 .2.6 6 .2.7 6.2.8 6 .2.9 6 .2.1 southern extension zones 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.1 IeEe -1 + ; 5 5 6 6 6 7 8 9 9 l0 1C 1 0 FIight capacity of S. damnosum L OCP/No .121 lvcu /84 page 3 Page 2110. Monitoring of the aquatic environment 10.1 Routine xoonitoring 10.2 Trials of new larvicides 10.3 Impact on non-target aquatic fauna of permethrin used as an adulticide 10.4 Analysis of data Training of scaff 21 22 22 22 11. 12. 13. Participation in meetings List of principal visit.ors Consultants and Eemporary advisers Other visitors 14. List of documents prepared by VCU 15. Conclusions and future prosPects Tables, uulps, figure l. General This half-yearly report covers the period from May to October 1983, it having been decided thaE the ciming of the half-yearly VCU reports should be brought into line with the entomological year, which comprises the following periods: November-Apri1 inclusive (dry season) and May{ctober inclusive (vet season). During the period under review the Unit continued Eo function uith its usual comPonent orSans: - Headquarters, based at Ouagadougou; - Division of Aerial Operations, with its two bases at Bobo-Dioulasso for the Western Programe Zone and at Kara for the Eastern Zonel - Division of Entonological Evaluation, also split into tto zones, couprising six sec[ors(Bamrko, Bobo-Dioulasso, Bouak6, Kara, Parakou and Tamale) which are subdivided into 24 sub-seccors (see Hap 1); as is done every year, an entoEological station was opered tenporarily aE Bandiagara (Mali) during the rainy season; - Division of Applied Research and Training, whose staff are distribut.ed amng Ouagadougou, Lom6 (Research on Insecticides), Bouakr! and Bobo-Dioulasso. As of 3t October the Unit trad 522 posts, 30 of them professional, broken dorm as follscs Breakdown by activitieg HeadquarEers AerialoPerat ions Entomological evaluat ion App 1 ied research Total Total strength (of wtrich: professional posts) 14 (4) 8 ( 8 ) 551 ( 1o) 39 (8) 622 (30) 22 23 23 23 24 24 26 27 13. 1 13.2 oCP/No .121 /vCtJ /84 page 4 Breakdown by country and activitY Benin IvoryCoas E Ghana Upper Vo1 ta Mal i N iger Togo Headquarf.ers Aerial operations Entonological evaluation Applied research 82 (1) 119 (2) 4 (0) 96 (1) 14 (4) 5 (5) 88 (4) 16(s) 87 (1) 14 (0) 3 ( 3 ) 75 (1) i9 (3) Total 82 (1) 123 (2) 96 (1) 123 ( 18) 87 (1) 14 (0) 91 (7) 2 2 0f these posts 26 (including six professional) were vacant at the end of the review period. On the other hand, two consulEants (one cytotaxonomist and one hydrobiologist) worked full time and a third (Deputy Chief of Unit) was recruited in mid-August. The main staff changes concerned the posting of the officer in charge of evaluation for the Westera Zorte and the transfer of the post of his counterPart for the Eastern Zone from Ouagadougou to Kara. The post of head of the Bouak6 sector was filled by the former holder of the Tamale post, who was himself replaced by the former "senior assistant enEomologist" from Bouak6. The aerial operations officer responsible for development of larviciding systetrs left Kara for Bobo-Dioulasso. Characteristics of the 1 983 rainy season 1 Movements of the ITF (Intertropical Front) To a greater excent than in previous years, the movements of the ITF were regularl.v monitored from week to week so as to obtain the best possible idea of the dynamics of the rainy season in the Programe area as a who1e. Specific data were obtained from the slnoptic stations at Bamako and Niamey and from the meteorological base at Odienn6 in the Ivory Coast. These data show the movements of the ITF to have followed the classical patEern in 1983, in contrast to the previous year when its persistence in the higher latitudes at the start of the year brought on a very early rainy season. Ar the end of April (end of the dry season), the ITF was for a time at the level of the 15"N parallel, whereas in March it had lain between the 9th and the 10th parallels. In Yay ir fluctuated between the 12th and the 16th and it was from the second week in June that it settled for good north of the 15th paralle1, thus bringing the entire Prograrme area under monsoon conditions. In July and AugusE it fluctuated between the 18th para1lel and the Tropic of Cancer. This northward movement of the ITF can be considered as following the usual annual pattern, despite its rather rapid progression over March and Apri1. It was at the end of August that it began its return towards lower latitudes: by che 35rh week (beginning of September) it was back at the 17th parallel, but its southward movement got going irreversibly only in the second fortnight of September, and by late 0ctober and early November it had reached the 9th parallel; this southward shift was more rapid in the eastern than in che western half of the Programme area. Then the harmattan began to blow ocP/No .121 /VCU 184 Page 5 from the start of October in the sub-sahel regions, spreading progressively to the whole of the initial Prograume area by the end of the month. The southern regions, comprising the phase IV area in the Ivory Coast and the southern extensions (Togo, Ghana and Benin), were still under monsoon conditions at the end of the half year. 2.2 Rainfall For a decade the sudan and sahel regions of West Africa have been everywhere afflicted by abnormally low rainfall and the 1983 hTet season was no exception. Table 1 gives provisional figures for the amounts of water collected at certain points in the OCP area. The rainfall coverage displays two different physiognomies demarcated by a line running roughly along the 9th parallel of latitude. To the north of this Iine, the 1983 rainy season displayed a normal physiognomy compared to prior years. The rains fe1-l regularly from the end of June, became heavier in July and August, and came to an end in September. In some cases, notably in the sub-sahel regions including the Sirba and upper White Volta valleys, rainfall was even above normal. To the south of this line, the rains were rather scanty except in the hi1ly regions of the upper Sassandra basin. Apparently, the 1ittle dry season lasting about one month that the southern regions experience each year was earlier and longer than usual. The regions most affected by this great shortage of rainfall were the phase IV area in southern Ivory Coast and the southern extension zones, where the amounts of rainfall recorded are two to three times below the 1982 figures. Global1y speaking, the geographical distribution of the rains was abnormal in Ehat the northern regions had relatively more rainfall than the southern regions. Nevertheless, their chronology followed the classical pattern, albeit with an early stop, since by October rainfall was very scanty or negligible over the entire OCP area. 3. Hydrological characteristics and vector habitat situation The hydrological conditions that prevailed during the 1983 rainy season rrere a direct consequence of the amount of rainfall, whether relatively abundant (as in the northern regions) or scanty (as in the south). The temporary watercourses began progressively to run again from May, but it was not until mid-July that discharge became general throughout the Prograrme area, when the rivers of the Bandiagara plateau, which are the most northerly in the zone under treatment, began to flow. The spates came very early in the basins of the White Volta and Red Volta, as also of theOti-Pendjari, which by the beginning of July was carrying large quantities of water hrith discharge rates of up to or over 100 m3/second. Flood t.ime came later on the watercourses of the Western Programte Zone and in the tributaries of the Niger river in Benin. In general, during this 1983 rainy season the discharge rates of the watercourses that rise or flow in the sudan or sub-sahel regions were sub-normal, though less so than the averagein most cases. The watercourses in question are the three Voltas and the Niger and Malitributaries of the river Niger. On the other hand, the Atlantic watercourses which rise in the Guinean savanna regions, hard hit by a drought of unprecedented severity, had discharge rates well below the average.In some cases these rates were up to 200 times lower than their mean values for the season. Comprised in this caEegory are the whole of the Bandama river system (White Bandama, Marahou6, lower Bandama), the Ivory Coast tributaries of the Como6 and of the Black Volta (some of which,like the Kohodio, flowed intermittently), the Benin tributaries of the river Niger, and most of the watercourses in the southern extension zones (ou6m6 and Mono basins). None of these rivers had the heavy spates generally observed during the rainy season. In particular, thedischarge of the lower Bandama remained below 15 m3/second throughout the rainy season at Tassa16, downstream of the Kossou and Taabo lakes, the filling of which and the operation of whose dams were greatly disrupted by the drought. The only exception was the Sassandra, whose waters come mainly from the massifs of Guinea. ocP/Ilo .121|VCU/84 page 6 In conclusion, a conspicuous feature of the hydrological year has been a severe drought in the southern regions of the OCP area, where the watercourses remained practically in their dry-season state, making possible better control of onchocerciasis vector habitats. One consequence of this drought was the very marked reduction in the possibilities for development of blackflies, both in the large complexes of breeding places on the lower reaches of the Atlantic rivers covered by the Programme and on their tributaries, few of which had discharge rates conducive to mass colonization by inrnature forms of S. damnosum s.1. In the more northerly regions, along certain watercourses rising in the sudan savanna regions, the rapid rise in water 1evels resulted in equally rapid submersion of the rock shelves, thus reducing the possibilities for vector development. This was notably the case with the White Volta river system, the rivers of the Prograrmre area in Niger, and the middle Black Volta. In the northernmost part of the Eastern Zone, the excess rainfall allowed larva1 habitats to persist for much longer than in previous years on the Sirba. Thus, in 1983, the hydrological situation on lhe watercourses of the Prograrlme area displayed rather special features that were put to advantage in the strategy and tactics of the weekly larvicide applications. 4. Strategy and tactics of treatmen! operations At the end of the dry season, the number of kilometres of watercourses covered by aerial treatment operations was estimated at 600 km, a very 1ow figure. But with the progressive setting-in of the rainy season and especially the onset of reinvasion, the various river systems were successively put under aerial treatment as and when the entomological situaEion so requirea (Map 2). It was in mid-July (28th week), when the rivers had all begun flowing, that the extreme northern limit of the aerial treatment zone was reached. This limit is marked by a line running through Bamako, Koutiala and Bobo for the Western Zone and L6o, Tenkodogo, Porga and Niamey for the easternhalf of the Progrartrne area. North of these axes, larviciding by aircraft was sporadic and mainly confined to the Bani at Daogosso and the river Koni (Map 2). 4.1 Aerial fleet deployment In l"lay the fleet T^7as, as always in the rainy season, strenglhened by two additional Hughes 500 helicopters, bringing the number of aircraft of this type from six to eight (four at each base, including one fitted out for survey work). In addition, a large (500 litres capacity) Bel1 204 helicopter was put into service for applying large quantities of Teknar and one of the two Pilatus Porter fixed-wing aircraft was replaced by a Turbo-Thrush with higher performance and larger capacity. Consumption in Eerms of flight hours is shown in Table 2 4.2 Larvicides utilized (Maps 3-8) During the 1983 rainy season all three of the larvicides available to OCP work were employed: the tr4ro organophosphorus compounds, temephos (Abate) and chlorphoxim, and a formulation of Bacillus thuringiensis serotype H-14 (8.t. H-14) made by the firm of Sandoz, Teknar(R). Abate was the only larvicide employed in the Eastern OCP Zone and in phase III West, i.e. in some 757. of the total OCP area. The watercourses in the remaining (south-western) 252 of the Programme area rdere treated either with Teknar or with chlorphoxim or with both those larvicides alternately. The principle adopted was application of Teknar at low water and its replacement by chlorphoxim when the discharge reached 50 m3/second or over, except on the Bandama dor,rnstream from lake Kossou where this limit was raised to 250 m3/second because of the special risk of resistance. I l aOCP/No .121/vcu/84 page 7 Three points should be noted: the reintroduction of chlorphoxim in the applications after several monthsr interruption; t.he treatment of the Black Volta with Teknar and chlorphoxim for the first time since resistance to organophosphorus preparations became apparent; and the clean-up operation on the lower Bandaua downstream from lake Taabo. The objective of this clean-up operation, consisting in high-dosage applications of Teknar, was to neutralize the huge reservoir of blackflies on the lower Bandama (from B6ri-Aboukro to Tiassal6) before the spread and propagation of the vectors. It began at the end of March and was terminated in the first week of July after 16 weekly cycles when, with the objective attained, applications of Teknar at normal concentration (1.6 mg/1itre/10 rnn) were resumed. After a 12-week period of suspension, treatments were recommenced on the ttlowertt Black Volta, first with Abate during the first fortnight of June, then with Teknar during the second fortnight, and finally with chlorphoxim starting in July. The entire river system downstream from the junction with the Bougouriba, together with the tributaries when there was any flow in them, were treated with chlorphoxim. This preparation was also used extensively in the basins of the Cono6 (August-Septenber) and the Sassandra (Ju1y-September) when the discharge rates exceeded 50 m3/second. On the other hand, the entire Bandama river systen, including the Marahou6 and Nzi basin, was kept on Teknar in view of the consistently very 1ow discharge rates of these watercourses throughout. the rainy season. 4.3 Intentional interruptions of aerial treatment in the rainy season These suspensions concerned mainly the rivers in phase II areas, where the entomological situation was good: the White Volta (from the 32nd week of the year to the 43rd), the Red Volta (froo the 38th week to the 43rd), and the Kulpawn and Sissili (from the 40th week to the 43rd). It nay be recalled that the rivers in eastern Upper Volta and the loop of the Black Volta have had no insecticide applications for several rainy seasons past. Also concerned was the Bago6, over the major part of its course downstream from Kouto, where larviciding was interrupted for five weeks (from the 34th week to the 38th), but was later resumed betlreen the junctions with the Kankela and the Bani in view of the deterioration of the entonological situation (see document OCP/EAC.4.14). The extreme lower Comod was also left untreated from mid-July to allow recolonization of the habitats by the vectors for various experimental studies (see section 9.1). Table 3 shows the amounts of insecticide utilized. $gma;y analysis of the costs incurred in phase II operations shows a saving of about 2 million CFA francs per week due to these suspensions of treatment. 4.4 Larvicid from the round As usua1, ground treatments were carried on during this rainy season by the entomological surveillance teams. Applications were made either in case of need due to failure of aerial larvicidinBr oE in specific breeding sites or zones selected for this nethod of control. This latter category includes: - the Bandiagara plateau (t-Iali) (see section 8); - the Tansilla region (Upper Volta); - the Markala, Dialanda and S61ingu6 dams in Mali; - the breeding sites at Niampourou and Nwokuy near Dddougou (Upper Volta); - the breeding sites on the Bal6 at Boromo (Upper Volta); ocP/No .121/VCU/84 Page 8 - the Baguineda irrigation canals near Bamako (Mali); - many other sites of local concern, taking into account the generally low rainfall in 1 983. 5. l,lonit.oring of Iarval habitats The routine weekly surveys took in some 350 breeding sites used as controls for monitoring the effect of aerial larviciding, together with about 40 other habitats regularly visited each week in parts of the untreated southern extension zone. These ground inspections of breeding places were backed up where necessary by prospections from helicopters where 1ocal problems had cropped up. In all, it was possible to conduct 10 such aerial surveys at various times during the rainy season. Particular mention must be made of the helicopter surveys of the Sirba with a view to mapping the breeding places on this watercourse, whose rate of flow this year seems to have been highly conducive to the establishment of onchocerciasis vectors over a longer period than in previous years. These investigations took place during the third week of October, and their main result was the detection of breeding places on fisherments dams. The main breeding site is sti1I the one at Garbey-Kourou on the lower part of the riverts course. The results of these surveys conducted on the ground, by river or from the air have on the whole indicated very good control of larval populations of S. damnosum s.1. in the Progranrme area. Rarely were densely positive habitats errco,r.rteiE-Ei7Gg the 1983 rainy season and the excellence of these results is explained not only by the refinement of treatment operations but also by the fact that, at the onset of the rainy season, foci of S. damnosum s.1. were rare owing precisely to the "absence" of females belonging to this ""rpl"- fr.* most of the river systems and that some of these foci could not afterwardsdevelop normally because of the below average rainfall. Nevertheless, owing to contamination from various foci, some breeding places did function sporadically. Map 9 shows the various zones where, aE some point during the rainy season, aquatic stages of S. darnnosum s.1. were detected, together with the three main causes of their becoming established in the treated part of the Programme area: (a) Deliberate suspensions of treatment: river systens of the White Vo1ta, of the Bago6 at M6t6la and Pankourou, of the upper Black Volta at Bafou1agu6, of the Sirba at Garbey-Kourou, of Tyenfala on the Niger, sites or reaches treated or not treated from the ground; extreme lower Como6 and Sassandra-Bagb6 basin, White Volta at Yabo where trials of new products, measurements of susceptibility to insecticides and studies on dynamics of populations were carried out. (b) The "awakening" of resistance to organophosphorus preparations, specifically to chlorphoxim. The reaches concerned are those of the extreme lower Como6, of the middle basin of the Sassandra and of the Bui region on the Black Volta in Ghana, at the end of che rainy season. (c) The unsuitability of the larviciding techniques and larvicides for the hydrological conditions of the moment, especially when they are changing. Teknar, in particular, always poses serious logistic problems and its dispersibility and carry stil1 remain poor. Into this category come most of the breeding sites that were able to function here and there either at the start or at the end of the rainy season: positive breeding sites detected on the White Bandama and the Bagb6 at the beginning of the rainy season and sites on the lower Bandama such as those at B6ri-Aboukro treated with Teknar, which were sporadically productive. Certain phase III East watercourses evidenced a similar situation: notably the M6 in its upper reaches, a tributary of the Kara, the upper K6ran(suspected), the Sota at Goroubanda, and the Gouroubi at Diongory (where utilization of a batch of Abate dating from 1976 nas incriminated). I oCP/No .121/vcu/84 page 9 It should be noted that in most cases readjustment of treatments (change of aircraft, of application systems, of larviciding techniques or of larvicides) enabled the problem to be nipped in the bud. It must also be emphasized that control of larval breeding sites during the 1983 rainy seasoo was facilitated by the very 1ow rainfall which prevented the big complexes of breeding places in the south-western Prograume zone from expanding and allowed longer utilization of Teknar, thus obviating premature resort to the organoPhosphorus compounds that generate or reactivate resistance. Consequently, recolonization of the breeding sites in the Progranrme area by onchocerciasis vectors was controlled everywhere except at the sites intentionally left out of account such as those of Yabo, Garbey-Kourou, the lower Como6 and the Sassandra. The better results obtained this year with Teknar are essentially due to exceptionally favourable hydrological conditions which allowed greater care and refinement in the handling of this preparation which, moreover, was better known after a yearts experience. Chlorphoxim treaEments, begun in the 26th week (1ast week of June), gave variable results according to the river basin. In the Sassandra and Black Volta basins these results were satisfactory in the aggregate, since in the course of over three monthst utilization of this preparation no "explosion" was noted either of aquatic simuliid populations or of biting populations. Nevertheless, Eowards the end of the rainy season, resistance to chlorphoxim was demonstrated in these two river basins following recrudescence of blackfly populations of the foresE strain. Results were from the start less good on the lower Como6, where the breeding sites at Amouakoukro, Amiakouassikro, Kabrankro, etc. reroained positive for S. soubrense/ sanctipauli ri ght from the first cycles of chlorphoxim treatment; these partial failures were confirmed by the exclusive identification of adults with dark wing-tufts, i.e. belonging to species presumed to be of forest type, in breeding sites where the presumed savanna-type species (withlight-colouredwing-tufts) are found under natural conditions. Monitoring of biting populations 1 General Monitoring of biting blackfly populations r{ras conducted as usual by means of numerous catches on human bait at the specific sites selected to evaluate residual transmission in the treated Programroe area or to supplement the pretreatment data in the southern extension zone. In all, some 286 capture points were visited on average each month during the 1983 rainy season, or 432 of the points coded. Some 1416 catching man-days were worked monthly during this rainy season, one of whose characteristics was that, unlike the previous one, it had inherited from the dry season an excellent entomological situation. At the end of April 1983, densities of biting females \rere extremely low in all the river basins, and at most of the capture points the monthly averages were nil or of the order of a few flies per man per day. Only the foci in the untreated Sassandra basin and on the Asukawkaw in the southern extension zone were productive, with bite counts exceeding 100-200 females per man per day. Nevertheless, May was as usual the month in which there was recontamination of part of the Prograrme area by non-indigenous vectors, mainly of savanna origin. This continued in June and July and spread to other areas, with higher concentrations in the zones usually affected. The month of July was characterized by the detection here and there of a few stray females of S. daonosum s.1., notably S. sirbanum trying to recolonize their original biotope now that the watercourses were again flowing. Thus, it was during the second fortnight of July that the most "northern" females of the year were captured: first at Garbey-Kourou on the Sirba in Ehe third week of Ju1y, and then at Lougourougoungou on the river that waters Bandiagara (the Yam6) during the fourth week. Another noteworthy occurrence in July 1983 was the capture of the first forest-type blackfly on the savanna rdatercourses, from which they had disappeared at the end of the dry season: the lower Black Volta at Tagadi and Bui (first week), and the White Bandama at the Niakaramandougou bridge (third week). 6 6 ocP/No .121 IVCU /84 page 10 No major development occurred during the second half of the rainy season except that the ful1 deployment of control activities resulEed in good overall loca1 biting populations in the treated part of the Prograrme area. (August-0ctober), control of the 6.2 Biting blackfly densities (see Maps 10-15) Taken in the aggregate, the data on catches recorded during the 1983 rainy season rank among the best OCP has had since the start of the Prograrmne, especially in its initial area. Vector densities and numbers of bites on human bait remained extremely 1ow in most of the river basins, except at the reinvasion sites, during the first half of the six-month period. Zero catches were almost the general rule in the heart of the Prograrme area, consisting of the basins of the upper Como6, the Black Vo1ta, the inlhite and Red Volta and their tributaries together with the Oti-Pendjari. Elsewhere, on basins such as those of the Bandama and Bagoti, the eastern tributaries of the Niger, while catches were not zero they were of the order of a few S. damnosum s.1. females per man per day. 6.2.1 Black Volta basin As in previous years, the entomological situation remained satisfactory on the lower and middle stretches of the Black Volta, but a marked improvement occurred on the lower stretch in contrast to 1982: in that year the reach from Tagadi to Bui (about 100 km) had been colonized in the rainy season by a large blackfly population mainly of forest origin. In 1983, average monthly catches scarcely exceeded 10 females per man per day on this reach, whereas they had been five to 20 times larger in 1982. It should be noted that in 1982 Abate treatments had selected out, on the lower Black Volta, a population of forest-type blackflies resistant to temephos. In 1983, by contrast, utilization of chlorphoxim enabled the explosion of a vector population on the lower Black Volta to be avoided. It should also be noted that the detection of the first S. daronosum s.l. females on the lower Black Volta was more or less synchronous with the establ ls hment in June-Ju1y of a small population on the reach of the lower Como6 lying between the junction with the Dior6 and S6ti6. The existence of a correlation between the populations on this reach of the Como6 and those on the lower Black Volta seems more evident this year than in previous years, but requires confirmation by an appropriate statistical calculation. Mention must be made of a loca1 upsurge of savanna-dwelling females in the region of Bafoulagu6 (upper stretch of the Black Volta) which occurred in September and was detected thanks to some Bellec traps set in place at Gossiamandara and Gu6na. Once the functional sites responsible had been located, their treatment quickly solved the problem. 6.2.2 Phase I1 river basins On the Red Volta, the White Volta with its main tributaries (Sissi1i, Kulpawn, Nouahou and Morago), and the Daka, the capture results are the best the Progranrne has had. The usual problems of residual local populations that affected places such as Nakong on the Sissili, Zongoiri rapids on the White Volta, Nangodi on the Red Vo1ta and Doungu6 were avoided this year. Very few capture points on this basin were productive and the monthly averages of the positive points scarcely exceeded one to three females per man per day, whereas ro 1982, especially, sporadic flare-ups had flawed the entomological results and caused considerable local transmission at the places referred to above. The breeding place at Yabo (northern Upper Volta, White Volta), left untreated, functioned for only a month and became quiescent when the rains stoPPed without having affected transmission. oCP/No .121 /vctJ 184 page 1 1 6 .2.3 Oti-Pendjari basins Leaving aside the usual seasonal problems (recolonization of tributaries such as the M6, the upper K6ra and the upper K6ran), the entomological results for the Oti-Pendjari were also very good, even on the Pans6ni-Toutionga reach, where there are generally loca1 Problems. 6.2.4 Como6 and L6raba basins In these basins, only two reaches were affected by S. daunosun s.1. females: rhe L6raba bridge-Gr6chan reach, owing to reinvasion, and the B6ti6-A16p6 reach (Como6), owing to suspension of treatments. On the first of these reaches, densities of reinvading females were low compared to the previous season, with monthly averages peaking at 25 females Per man per day at Ehe bridge Lver the L6raba in July. No blackflies of forest origin were caPtured in the L6raba basin during this rainy season. On the second reach, which corresponds to the natural biotopes of S. soubrense and S. sanctipauli, female densities were high with monthly f igures reaching and exceedingB6ti6, on the other hand, densities1000 females Per man Per day, especiallyat Koutoukro. At were lower, though still considerable, being of the order of 500 females Per man per day. A11 blackfly identified in the Koutoukro focus (B6ti6-A16p6 reach) during the 1983 rainy season were of forest type. This focus seems to have operated "in a closed circuit" with no input of allogeneous vectors from outside. Higher uPstream on the lower Como6 (Kabranko and Amouakoukro regions), on the other hand, the intermittent increase in catches in some weeks of July and August suggests sporadic influxes of females from Koutoukro due to simple linear dispersion. In the rest of the Cono6-L6raba basin, the entomological situation was highly satisfactory, in particular at Toup6 and Sarakro (Corno6), localities generally affected during the rainy season, where the monthly averages were often below five females Per man per day' compared to bet\reen l0 and 30 in 1982. 6.2.5 White Bandama basin After some problems at the sEart of the rainy season (reinvasion combined with difficulties in applying Teknar), the enEomological situation became satisfactory by of June and beginning of July and remained so for the rest of the half year. Two developEents in comparison to the previous rainy season are noteworthy: the end - the bringing under control of the artificial breeding places at Badikaha (pumping station), which in 1982 had been responsible for some local transmissionl - the disappearance, both among catches and in the breeding places, of forest-tyPe species,-rti"t this year did not colonize the basin of the White Bandama and of its main tributary, the Bou; at the very most an occasional biting female assigned to the species S. soubrense was identified, notably at the Niakaramandougou bridge (on the Bandara)Ed "tJ6ding site No.3 on the Bou. It must also be emphasized thatcytotaxonomic identification of larvae indicated the presence only of S. sirbanum, and S. damrosum s.s. practically since July 1982, when Teknar applications began on the White Bandame These results, together with those on t.he L6raba, seemingly lend suPPort to the hypothesis that it is possible to eliminate S. souqrenge from savanna regions over a long pl.ioa by soundly applied treatment with an etfeclive insecticide, when hydroclimatic conditions are favourable. ocP/No .121/VCU/84 Page 12 6.2.6 Lower Bandama and Nzi basins The "clean-up" operation enabled the Large blackfly-producing foci on the lower Bandama ro be controlled. Eight weeks after the start of the oPeration, the biting blackfly population was disappearing, whereas previously over 1000 females Per man per day had been caught every week at the Gauthier fal1s1 these excellent results were maintained throughout the rainy season, for monthly average catches did not exceed three females Per man per day, whereas even with this yearts low discharge rates there would have been reason to fear daily peaks of 2500 bites per man per day. The neutralization of these foci seems to have resulted in there being no contamination of reaches and basins upstream. In contrast to previous years, no proliferaEion of forest-type vectors was noted on the Nzi, the Marahou6 and the White Bandama. Similarly, certain reaches of adjacent rivers such as the lower Como6 in the Amouakoukro region and, further away, the lower Black Volta, \^7ere not infested this year by large blackfly populations, in conErast to previous years. It seems, therefore, that the clean-up operation on the lower Bandama has 1ed to an improved enEomological situation on the niddle Como6 and the lower Black Volta, but this presumed correlat.ion needs to be verified by an appropriate statistical calculation (see section 6 .2.1) . In the Nzi basin, a loca1 problem arose ia August in the vicinity of Dimbokro. The blackfly population that resulted from it (average 15 females per rnan per day) was very quickly brought under control by readjustment of the treatment schedule. 6.2.7 Red Bandama basin (Marahou6) Apart from the sites usually affected by reinvasion, which in any case l^ras moderate this year (Kato, Mermis breeding site and Kongasso), the rest of the Marahou6 was free of blackflies The large breediog sites at Danangoro qrere not productive: in contrast to previous years, when monthly averages sometimes reached several hundred per man per day, catches remained below one blackfly per rnan per day throughout the 1983 rainy season. This was thanks to well-applied larviciding, helped considerably by the 1ow discharge rates of the I^Tatercourses. 6 .2.8 Sassandra basin Two kinds of situation vrere encountered, one to the north and the other to the south of the latitude of Bafing. On the southern side (northern limit of the evergreen or semi- deciduous forest), capture densities vrere rather low t.hroughout the half year. At the Semien ferry, monthly averages remained below 30 females per man per day (usually well below). To the norEh of this axis, i.e. in the valleys of the Bagb6, the Boa, the Sien and the Tiemba, vectors were able to proliferate either by reinvasion or through contamination due to linear dispersionor Ehrough both phenomena combined. Monthly averages remained consistently high and even very high from May to Ju1y. It is interesting to note that at the start of the rainy season the populat.ions on the upper Sassandra basin, including Ehose at Semien, consisted mostly (around 60-907") of savanna species; towards the end of the rainy season the proportions were reversed, the time the reversal occurred being about the middle of July. 6.2.9 Nieg1: !egi" This includes all the rivers in the north-\restern, northern and eastern parts of the Ereated Prograume area. Entomological surveillance gave what are no\^7 classic results in the rainy season, with reinvasion of the lvory Coast-Malian and Beninese tributaries, and excellent results on all the other \4ratercourses, including those of the Bandiagara plateau. The only noteworthy fact about this basin is that the Garbey-Kourou breeding site on the Sirba was productive for the longest period since the start of the Prograune: a local POPU lation of S. sirbanum remained settled there for over two months in September and October, with monthly averages of 65 and 70 females per man per day respectively. A peak of 343 females was even obtained on 2 November. This blackfly population comprised only 1O-4OZ of parous females. oCP/No .121 /vcu /84 page 13 6.2.10 River basins of the southern extension zones In these basins, collection of entomological data proceeded according to plan with a vrew to strengthening our knowledge about the annual fluctuations of blackfly populations in each of the basins concerned and correlate them with hydrometric data. At the start of Ehe rainy season in May, blackfly populations were confined to the only basin where there was any discharge, namely that of the Asukawkaw, and practically zero in the other basins, namely those of the Ou6m6 and Mono. June and July saw a progressive spread of the vectors from the southernmost ParEs of the southern extension zone, where they first appeared, to the upPer basins. The peak production time was August, when the monthly averages were generally in excess of 200 females Per man Per day and even 500 for the most productive sites. Though high, these blackfly densities are in general lower than those of previous years, doubtless because of the less favourable hydrological conditions. By the end of the rainy season in October, blackfly densities were beginning to decline with the drying-up of the watercourses. It should be noted that in "normal" hydrological conditions it is in September and October that the highest capture rates are recorded in the southern extension zones. In 1983 this period was markedly shorter owing both to the late arrival of the vector populations and to their early extinction. The Asukawkaw, a permanent river where blackflies are present all the year around, is always an exception to this rule. 5.3 Reinvasions Order of events To the west, on the pattern of previous years and following the northward movenent of the ITF, the first river basins Eo be affected by reinvasion were those of the upper Sassandra, the Yarani and the Marahou6 on their upper stretches. The ITF reached the Eost northerly OCP regions by the end of April (17th week); but it was in mid-May (20th week) that it finally settled there and moved towards higher latitudes, thus bringing the entire Progranrne area under oonsoon conditions (see section 2.1). The first sites to be contaminated by invading blackflies were those at Massadougou (on the Sien), Niamotou (on the Boa), Kato (on the Yarani) and Mermis (on the Marahou6). They began to be affected from the end of April 1983, at a time when there was not enough flow in the rivers concerned for proliferation of the aquatic stages of onchocerciasis vectors. At the beginning of May, exogenous females were captured simultaneously on the Bou (at breeding site No. 3) on the White Bandama and on the L6raba. At the end of the same month, a few sporadic females were detected at Nab6re on the Bougouriba. Note t.hat during a trapping experiment at the bridge over the L6raba, gravid savanna-type S. dannosum females were captured from t.he end of April. These were doubtless the very first reinvading blackfly to have reached the L6raba valley. The progress of the reinvasion phenomenon towards the more northerly regions in Mali went by "steps": the upper basin of the Baou16 and the lower stretch of the Kank6laba were affected first (mid-May) followed by the niddle reaches of the Baou16 and Ehe lower stretch of the Bago6 at the end of May; it was not until the end of June that the Faya was reached. In the Eastern Zone the Sota basin was the first place to be heavily colonized, from the end of June; the M6 va11ey was not affected until towards the middle of the same month. Note that, while this reinvasion of the M6 and the Sota was confirmed by the mass arrival of savanna-dwelling females (S. squamosum on the M6 and S. sirbanum and S. damnosum s.s. on the Sota) with high rates of pari ty and infestation with O. volvulus, the situation was nevertheless complic ated by the presence of nulliparous flies in the catches, reflecting theproximity of rivers left untreated or treated only along part of their course. OCP/No .121 /vcul84 Page l4 7 Extent of reinvasion Map i6 and },laps 10-15 bring out a number of facts: is to the liroits of the treated Programme area the more intensely it - The nearer a basin is affected. - The reinvasion of the west, which started quite gradually in May, reached its high point in June and July and began to recede from the end of July and beginning of August; this contrasts with the 1982 scenario (sudden onset in March, very high peak in May, cspecially in the Ivory Coast, then sudden and early decline) and is attributable to the difference in rainfall between the two years. - Note that certain foci which had been affected in previous years owed their protection to the containment of "endogenous reinvasions" by the suitable and timely treatment of potential sources of reinvasion located within the Progrartrne area (north-western Ivory Coast) . - To the Lrest, the 1983 reinvasion was comparable to the one in 1982, with slightly higher densities of females but covering a smaller geographical area. Evaluation of onchocerciasis transmission (Maps 17 and 18) With the end of the entomological year (31 October) , it was possible to determine the provisional ATps (Annual Transmission Potentials) for the year 1982-1983. I'laps 16 and 17 show maintenance of the good results obEained in previous years and an improvement compared to 1981-1982. There rrere, in particular, appreciable iuprovements in foci difficult to neulralize like those on the White Bandama and lower Bandama (Ivory Coast) and on the Bui (Ghana), or certain habitats in northern Ghana, northern Togo and the Atacora Region (Togo-Benin). Out of some 170 capture Points t.aken into account for a p 822 show values for that index below the tolerability limit of larvae per man Per Year. reliminary estimate of ATPs, 100 infective O. volvulus 7 1 The initial Prograrune zone The results here are particularly satisfying for, except in the main reinvasion zones, the ATP has everywhere been kept below the threshold of 100 and there has therefore been practically no autochthonous transmission, thanks to close surveillance and good control of pre-adult habitats. In this zone, ATp values are not only within the tolerability limits but generally at or very close to zero. Such ATP values are met with in the phase II and part of the phase r areas: basin of the white Volta, the oti and its right bank tributaries, upper and middle Black voIta, upper and middle como6, Banifing IV and V basins. In more peripheral regions, while ATps of local origin were recorded, their values did not exceed 20 larvae per man per year. 7 2 Reinvasion zones In reinvaded areas such as the eastern border region of Mali (Baou16, Bago6, Kanktilaba, Faya) and the L6raba, ATPs of around 100 or ovef were still being recorded' In the White Bandama basin, only the Bou recorded an ATP slightly above 100, much lower than the 1982 figure. The limit of 100 was exceeded by only one locality each on the Black Volta (Akanyakrom) and the Marahou6 basin (fato), where the improvement compared to the previous year is particularlY marked. ocP/No .121|VCU/84 page 15 A point worth stressing is that the interruption of transmission on the 0uassoulou-Ba16 reach, inundated by the S6lingu6 lake, has been confirmed. Results are still unsatisfactory in the upper Sassandra basin, where high transmission rates still prevail. These high rates, like those experienced in the M6, Kara and Sota valleys to the east, are due not only to the reinvasion phenomenon but also to btackfly recolonizing these vatleys by simple radiat or linear dispersion, because of the proximity of untreated zones. Except on the Sassandra, positive MTP (Monthly Transmission Potential) values correspond to periods of reinvasion, transmission being zero before this occurs and ceasing after it has died away. To the east, ATPs \rere markedly lower on the Kara, the K6ran, the Alibori and the M6krou but remained well above the tolerability limit on the M6 and the Sota. 7.3 Forest zones Good results were maintained on the lower Bandama throughout the rainy season, during which transmission was interrupted. The transnission that is reflected in positive ATP values corresponds to the low-water season, before the start of the "clean-up oPerationrr. Six capture points were chosen for special investigations with a view to establishing the annual transmission potentials in untreated forest regions: Soubr6, Bidoubr6 and Louga on the lower Sassandra, Akakro on a tributary of the Agn6bi, and Kotoukro and B6Ei6 on the lower Como6. The provisional ATP and, especially, ABR values are, as hras to be expected, high: Soubr6 1 Bidoubr62 Louga2 s6ti6 Kotoukro Akakro2 ATP ATP ATP ATP ATP ATP ABR ABR A3R ABR ABR ABR 405; 1851 ; 7 42; 17 4; 1268; 4584:' 129 123 50 66 208 119 265 826 710 403 331 039 The transmission reflected in these figures is maintained almost exclusively by foresr vectors in their original biotopes, namely the evergreen forest. Identification by the wing-tuft uethod of the biting females and also of che adults originating from the breeding sites corresponding to the capture Points has indicated the presence of almosE 1002 forest-type blackflies. Whereas on Ehe Sassandra and the Como6 the species concerned was Ugbrense, it would appear from cytotaxonomic identif ication that the blackfly populations oi fuakro are composed of S. squamosuu and S. yahense. The findings will be interpreted in conjunction with the parasitological, clinical and ophthalmological data collected at the same sites. 7.4 The southern extension zone The vectors rJere able to develop in the absence of treatment and carry on local transmission, buE two distinct situations become apparent when the basin of the Volt.a lake and those of the Mono and the Ou6m6 are considered. On the one side, transmission continued throughout the year owing to the perlnanence of the watercourses (Lake Volta), while on the other (Ou6m6 and Mono) it is seasonal. It is interesting to note Ehat this seasonality has been affected by the climatic vicissitudes of recent years with their abnormally long dry seasons, resulting in shorter periods of contact between man and vector. In 1983 the highest 1 2 For eight months t catches For l0 monthsr catches. ocP/No .121/VCU/84 page 16 transmission rates in the Oudm6 and Mono basins were recorded in August and September and, though the ATP and ABR values were high, they were not as high as those recorded at the time when surveys began in the southern extension zone. 8. The campaign on the (Mal i ) As in the two preceding years, the onchocerciasis control campaign on the Bandiagara plaEeau was conducted ent.irely on the ground with the Participation of the 1oca1 village conrnunities. It began in mid-July and is to continue until the end of the year. Captures are at present made and larviciding done by the entomological surveillance teams of the Programe, with the guided participation of the village co'nmunities through the instrumentality of indigenous first-aid workers trained by the Programe. The experiment in involvement of these conrmunities, which in 1982 Eook in only four villages in the Yam6 depression (Bandiagara river), was extended this year to the whole of the plateau. Taking 1982 as baseline, the following progress has been achieved: - training of a larger number of first-aid workers; - Eheir initiation into the identification of the aquatic stages of blackfly; - health education of the village populations on the subject of onchocerciasis. The plan of action proposed in April 1983 has been carried out according to schedule. The catches were made regularly by the Prograrrme teFms every other fortnight at the eight main entomological surveillance points. The checks on 1arva1 habitats were mede weekly, those found positive being treated manually with Abate and rechecked only the following week on an appropriate circuit plan. Two Progranmre teams took responsibility for these applications from the ground. Excellent results were again obtained this year and the larva1 populations were neutralized as soon as detected. Despite a relatively high river flow rate, only a very few biting blackfly were caught on the Yam6 at Lougourougoungou (the plateaurs most productive breeding site), on the downstream side of Bandiagara and at the breeding sites of the upper Diama at Lampi6ra. These catches showed no evidence of transmission taking place. Elsewhere, capture rates were zero. operational and applied research I Screening of new larvicides A large number of preparations were tested, either in minigutters, or in troughs, or in river conditions, by VCUts specialized team based at Lom6. To date, no carbamate has proved both effective at 1ow dosage and correctly formulated Other preparations of this family remain to be tested. Among the organophosphorus preparations, the only one that does not yet display cross- resistance with temephos and is sufficiently selective in its effectiveness is Azamet.hiphos. It has been Eested successfully in river conditions. Particular attention has been accorded to the synthetic pyrethroids, notably deltamethrin, cypermethrin and permethrin. The last of these, formulated in an emulsifiable concentrate, gave in river tests very promising results at a low dosage (0.015 rilglLitrel 10 mn) in relation to target and to non-target fauna. 9 9 OCP/No .121/vcUl84 page 17 A new formulation of B.t. H-14, Bactimos(R), has aroused great hopes: after some very promising trials in grrtters by the IRTO teams at Bouak6, trials performed in rivers by VCU in Ocrober showed that this preparation, utilized at 1.6 mg/1itre/10 mn without prior dilution under operational conditions, had a carry of at least 7-10 km. Unfortunately, the industrial batches manufactured since the original batch have not confirmed these hopes, despite the wide variety of application methods tried in river conditions and numerous trials from the ground (see section 9.7). Trials are continuing at Bouak6 with experimental batches to elucidate the reasons for these inconsistent results. Meanwhile, improved formulations of Teknar have been tested in minigutters, again with promising results, on the strength of which operational trials in river conditions have been p 1 anned . A detailed plan for large-scale testing of the principal larvicides, including an evaluation of their effects on non-target fauna, has been prepared for implementation in the couing monEhs, on the formulations of B.t. H-l4, permethrin and Azaroethiphos, as recotr*ended by the Expert Con*ittee. Following the specialized VBC/OCP meeting held at Geneva in August, a large number of growth inhibitor (IGR) formulations have been received by VCU and suitable protocols, including follow-up of their effects on all the development stages of the vectors, are being drawn up bot.h at Bouak6 (IRTO) and at Lom6 (VCU). 9.2 Measurement of suceptibility to insecticides Since chlorphoxim was brought back into use in May-June, VCUrs specialized teams have been closely monitoring the reappearance of resistance Eo this insecticide in S. damrosum s.1. As reporEed above (section 5), this occurred almost immediately on the Como6, in S. soubrense- sanctipauli, whereas treatnents continued to be effective in the Sassandra basin and on the Black Volta. By the end of 0ctober, however, signs of a resistance which \das to be demonstrated early in November in t.he forest species were becoming apparent on the Sassandra and the Bagb6 and in the Bui Bend (Black Volta) where, though strongly suspected, it had never been actually proved in previous years. The situation as regards resistance to organophosphates is depicted in Map 19. Note that the small isolated population of temephos-resistant S. damnosum sirbanum identified at. the beginning of the year in the forest zone on the lower Bandame has apparently been unable to reconstitute itself, thanks to the clean-up operation and the other measures taken (in particular final cessation of the use of organophosphates on the Bandama basin). It has not been possible to detect further resistance to temephos, though a close watch was kept. During this period two new techniques came into being. VCU developed a test for measuring the susceptibility of adults by topical application which enables resistance to chlorphoxim and temephos to be detected in wild females, and which shows satisfactory concordance with the results of measurements of larval susceptibility. Secondly, IRTO developed a met.hod of reproducing a current necessary for supplying nourishment to larvae in order to measure their susceptibility to B.t. H-14. Both methods have already been brought into use for routine monitoring. 9.3 Vector role of species of the S. damrosum complex In the south-western part of the Programne area, the cumulated results of identifications and dissections performed in recent years on thousands of blackflies allow the following preliminary conclusions to be drawn. The proportion of forest species colonizing wooded savanna regions is extremely Iow - generally below 12; these species have never been identified in dry savanna areas. In forest and forest/savanna mosaic areas, on the other hand, they represent betweer^ 7OZ and 1002 of the anthropophilic biting population; in intermediate zones of light forest or humid savanna the proportion of such species in these populations sometimes exceeds 502. ocP/No .121 /VCU / 84 page 18 The forest species are the sole vectors in dense forest zones; they apparently play nopart in the transmission of onchocerciasis in wooded savanna ancl dry savanna zones, rvhere transmission is carried on exclusively by the savanna species. In light forest or humid savanna zones and in forest,/savanna mosaic regions, the ATPs are the resultant of the savanna species and the forest species of the S. darnnosum complex by indis t ingu i shable larvae of 0. volvulus. The part p1-ayed by savanna species is always preponderant as far as densities of infective bites are concerned, and often dominant as regards the ATP, even if the percentages of forest-type bit.ing blackflies greatly exceed those of savanna blackfliesl in such areas, these forest species may neverEheless be responsible for ATPs above the accepted limit of tolerability, though the epidemiological significance of the phenomenon has not been determined. The results of other studies performed between May and September by two consultant.s in Togo and Benin are still being analysed. They confirm that the rates of infestation of S. damrosum/S. sirbanum are higher than those of S. squamosum, which are themselves above those of S. sanctipauli soubrensel the infective parasite loads of this latter species pair are typically higher than those of the other species. That means that where the pair is well rePresented (e.g. in southern Togo) it can play an important part in transmission, whereas in the xoore northerly regions of Togo and Benin that role is certainly very limited owing to the extremely smal1 numbers of biting individuals. Both to the west and to the east, whether in guinean savanna (Ivory Coast) or in the t'Dahomey gap" (Togo), S. soubrense can therefore contribute to h igh ATPs in a proportion above the limit of tolerability, in foci where the species is associated with S. damnosum and with severe ocular manifestations of the disease. Only by a parasitological investigation into the homogeneity of the "species" 0. volvulus and the identity of the strains of this parasite transmitted by each of the vector species will it be possible to determine the epidemiological risk represented by the various species of the complex and in particular those which are organophosphorus resisEant. It has also been confirmed experimentally in Togo that the S. soubrense from the southern part of the country al1ow normal developme nt of the microfilariae of savanna 0. volvulus whereas in the same region S. squamosum is a poor transmitter of those same microfilariae. In the north of the country (sudan savanna), on the other hand, this latter species lends itself well to the development of microfilariae of savanna origin. A11 the species and species pairs covered by the survey displayed zoophilic tendencies; they all carried infective stages of onchocerca belonging to species enzymatically different from O. voIvulus. 9.4 Studies on the reduced catching and trapping network Since the beginning of 1983 VCUrs entomological evaluation network had been slirmred down by the elimination of two sub-sectors (Porga in Benin and Tenkodogo in Upper Volta), and of one or two capEure teams in four others (Di6bougou, Bolgatanga, Niamey and Ouagadougou). In all_r 94 capture teams operated during the rainy season from 30 bases (six sectors and 24 sub-sectors) , including the southern extension zone. The innovation consisted in experimentally reinforcing certain capture points with improved Bellec traps (adhesive-covered aluminium plates mounted on floats and moored in the rapids). The pilot study was conducted in April in the Bobo-Dioulasso sub-sector at some dozen points included in the reduced network plan. For reasons beyond the control of OCP, it could not be extended, as had been planned, to all the phase II areas. The final results are being assessed but the following facts can already be reported: - the improved trap is attractive and remains so for several weeks irrespective of atmospheric and hydrological vicissitudes (rain, submersion, etc.); it can be visited only once every four or five days with reasonable assurance that the insects caught will be well preserved; oCP/No .121 lvcu /84 page 1 9 - it is operational and the supervision of a network of plates can easily be managed by a sub-sector team. On the completion of this pilot study five capture points had been monitored experimentally by this method for 22 weeks (from June to October) by the Bobo-Dioulasso sub-sector; a convincingly successful first experiment in associating a village conmunity in the monitoring of the traps is an encouragement Eo VCU to reproduce this kind of trial in other regions; - its effectiveness is borne out by the concordance of the results with those of normal captures: in most. cases of zero catches on human bait, the traps confirmed the absence of 1ocal populations; on the other hand, at the bridge over the L6raba the Erap detected the first reinvading blackflies several days before the capturers did. In the Presence of a smal1 blackfly population (Gossiamandara, on a tributary of the upper Black Volta) the plates recorded the existence of this colony at the same time as the capEurers did, and in the same region, in the absence of capturers, the plates alone enabled an unsuspected Iocal colony to be detected (and subsequently neutralized)(see section 6.2.1). Fina11y, with this pIate, as with its original version, samples can be made of impressivel-y large populations of blackfly species that are not 0. volvulus vectors - its effectiveness reuains, of course, purely qualitative (including with transmission), but the actuality of the warning (sentinel) role of these seems confirmed. Subsequent studies and analyses will be centred on the the trapping network and on comparative cost-effectiveness studies under operational conditions. regard to new plates exEension of different 9.5 Studies on dispersion These were conducted as part of the routine entomological surveillance activities, with six temporary capture teams in each zone as reinforcement for six uonths. In the Western Zone, only linear dispersion studies were undertaken this year. They were conducted on the river Faya (Ma1i) as in the two previous years, with a view not only to confirroing the previous findings buE, especially, Eo evaluating the adulticiding operations undertaken in the zone. In the Eastern Zone, on the other hand, radial dispersion studies were conducted for the first time on an intensive scale. They were carried out on the Sota at Gbass6 (Benin), which is one of the most prolific spots in the zone for blackflies. The principle adopted was to catch the flies along a longitudinal transect (Faya) or a Eransverse one (Sota) at points situaEed at known distances measured as the crow flies from the principal capture points, located near the watercourse and serving as point of origin. The results of the linear dispersion study on the Faya confirmed those of previous years, particularLy 1982: the 1983 observations again indicate that the presence of breeding places on the reinvaded reaches is associated with concentration of al1ogeneous S. damnosum females. Hence, the highest densities of biting S. darmosum/S. sirbanum females were found at the capture points located near or at rapids or stretches of fast current, conducive to the development of onchocerciasis vectors (see Fig. 1). The case of the Gara capture point is revealing in this respect: situated as it is about 6 km as the crow flies upstream of the bridge over the Faya, close to breeding sites, more catches are made there than at any other site located further downstream and possessing no potential habitats. The 1982 and 1983 studies showed, too, that with the submersion of the Gara breeding sites blackfly populations are tending to disappear from the area. The results of the radial dispersion sEudy on the Sota are sti1l being analysed. Nevertheless, even though they show a marked reduction in biting populations with increasing distance from the breeding sites, the data accumulated over nearly four months of study (frorn the end of June to the end of October) seem to point to certain differences from the situation usual Iy observed in the Western Zone. The captures of S. daurosum/S. sirbanum along the transect, which rDeasures 12 km in either direction fron the Gbass6 reference point, contained a raEher large proportion of nulliparous females, anounting in some cases to 152 of the total nuober dissected. It also seems that Ehe belts of riverside land affected by the dispersion from the rratercourse are wider than in the west. OCP/No .121/vcU/84 page 20 The reason for these differences between the radial dispersion of reinvading females the Sota and what is observed on the Baou16, the Ouassoulou-Bal6 and the Faya in the west be the proximity to Gbass6 of tributaries not subjected to treatment. Nevertheless, the general pattern of this radial dispersion remains the same in that blackfly population decreases to an appreciable degree as soon as one moves away from the of the watercourse. on might the banks 9.6 Larval life-span studies The studies carried out on this subject in May 1983 in western Ivory Coast, in guinean savanna councry, were a continuation of other studies previously performed in other regions of that country. The results obtained on mixed populations seem to indicate a shorter pre-adult development cycle in savanna species than in presumed forest species; its duration is in the region of 1 1 days for the larval life span at the season chosen for the study (temPerature 27-31"C) . This latest finding has to be correlated with those obtained in December in the forest with S. sanctipauli/soubrense on the lower Bandama (12 days at 25-30"C) and in May with S. "oG6". (""t""t"d by th" effect of temephos treatment) in guinean savanna country on the I^Ih ite Bandama (8-9 days at 29-33"C). It is not always easy ro distinguish the part played by environmental factors (water temperature, coefficient of flow, concentration of suspended food particles' etc.) and factors pertaining to the identity of the species in the interpretation of these differences, and the studies will be continued under differenE bioclirnatic conditions; but already now these prelininary results confirm, if any confirmation r{ras needed, the soundness of the weekly periodicity of larviciding in savanna areas. 9 7 Evaluation and testing of B.t. H-14 app lication systems Impromptu recourse to boom atd nozzLe systems to couPensate for the shortcomings of the formulations of B.t. H-14 has led VCU to develop a methodology and a systematic progra*e for testing the systems on the ground. The principle is Eo measure an "index of suspensibility" theoretically expressing the dispersibility and hence the effectiveness of the preparation in river conditions. This index is measured in series of containers spaced regularly along the path followed by the helicopter and over the area covered by the insecticide "cloud". Also recorded are the size and distribution of the insecticide droplets in this cloud. The validity of the index and then the methodology were tested with Teknar. It was then possible to make the following observations. With a 1ow-viscosity Teknar the number of rrozz1-es (two or four) makes no difference but with a high-viscosity Teknar the use of more than three tozzles results in coalescence of emitted substance aE the centre of the cloud (massive, non-dispersible release) whereas at the periphery small-size droplets compatible with good dispersibility are observable. Improveuents in the boom and nozz1e designs with a view to homogenizing the cloud of B.t. must therefore be envisaged; but t.he superiority of the boom and nozz1-e system to the rapid-release systen with restrictor used for Abate is nevertheless confirmed for applicaEions of Teknar. This restrictor system was nevert.heless utilized for testing various formulations of Bactimos in trials which confirmed the results obtained in the field and hence the validity of the Eest, both with the restrictor and with the boom arrd nozzle system. Studies are continuing to perfect the method, aPply it routinely to all new formulations of B.t. H-14, and make adequaEe improveoents to the applicaEion systelDs. ocP/No .121lVCtJ/84 page 21 9.8 Adulticide trial A trial of adulticiding \4ras carried out on the river Faya (near Bamako) in August with a view Eo destroying the populations of reinvading females in the gallery forest. Some 2.1 kro of gallery (30.3 ha) was treated up to a height of over 2.5 m with an emtrlsifiable concentrate (250 EC) of permethrin (Ialcord(R)1 aituted in gas-oil to 4 g of active preparation per litre and applied with seven spraying machines (six Hudson X and one Igeba) by seven operators assisted by four labourers. The zone was treated in eight days and nearly 4000 litres of gas-oil and Talcord mixture were used (315 g/ha). Following the operaEion, the adult blackfly populations, already on the decline, remained negligible for the ensuing month. It was unfortunately impossible to avoid contamination of the river, but its effects were not very severe (see section 10.3). The other lessons learnt r"rere the following: - such an undertaking is difficult and arduous and its efficiency low because of the plant cover; it must be meticulously prepared and the operators must be numerous and well equipped; long-range spraying machines (Igeba type) are preferable; - the cost of such an operation amounts to some $ 62 per hectare or nearLy $ 900 per kilometre of gallery, but these costs would be reduced by 452 if the gas-oiI were replaced by water. 9.9 Mapping studies Detailed mapping was undertaken on the lower Bandama in order to try and relate breeding site productivity to water leve1 and develop appropriate larvicide application methods taking into account the specific coefficient of flow in the najor complexes of breeding sites that are oft.en associated wit.h treatment problems. By way of indication, Map 20 represents the B6ri-Aboukro breeding site, where there appeared early in the year an isolated forest population of S. damnosum/S. sirbanum resistant to Abate. Depending on the season and the place in this breeding area the width of the rapids varies between 0.2 and 2.3 km and the course followed by the water from the upstrean to the downstream end between 3.5 and 5.5 km. 9.10 Flieht capacity of S. damnosum A consultant undertook in Bamako a laboratory study on the influence of humidity, temperature and infection by O. volvulus on the theoretical flight capacity of S. daurosum fem:les. 10. Monit.orins of the aquatic environment 1 0. 1 Routine monitoring This continued, keeping t.o the pre-established periodicity. A US$ 7000 grant agreement was signed with the Directorate of Animal Production at Lom6(Togo) , which is to undertake the ichthyological monitoring of the Togolese rivers. A US$ 5500 grant agreement was signed with the Directorate of Fisheries at Cotonou (Benin), which will take care of the aquatic monitoring (fish and invertebrates) of the Beninese rivers;this is an ext.ension of an existing contract. A US$ 9200 grant agreement was signed r^rith oRSToM (France), which has undertaken to draw up and have printed a catalogue of the freshwater fish of the Prograuune area and its extensions. OCP/No .121lvcul84 page 22 A US$ 3000 grant agreement was signed with the Higher Polytechnic Institute at Ouagadougou (Upper volta), which is to carry out monitoring of aquatic invertebrates at two stations on the Red Volta; this is an extension of an existing contract. In the encire Progranune area under larvicide treatment the situation remains normal. In some areas of the Ivory Coast where Teknar was used for a large part of the year it can be considered better than in previous years because certain taxons that had disappeared or become rare are now more abundant. The same applies to Upper Volta, where, because treatment has now been suspended for several years on the Red Volta (P6 bridge), a faunistic structure identical to the pretreatment one has been able to re-establish itself. This year, then, the persistent low water made it possible to suspend larviciding for long periods in some regions or use Teknar all the time on some stretches. These interruptions have been rather advantageous to the invertebrate fauna; on the other hand, the absence of spate is, as always, detrimental to the fish populations, A study aimed at demonstrating the negative effect of absence of spate on the following year's fish catches is now in progress. 10.2 Trials of new larvicides During this half-year the impact of five new larvicides was tested on the non-t.arget fauna. Of these, the pyrethroids proved ralher toxic for invertebrates at the concentrations utilized (OMS 3002 at 0.2 ppm/10 mn; deltamethrin A and deltamethrin B at 0.0005 ppm/10 mn; and permethrin at 0.02 ppm/'10 mn). Some of these larvicides are, however, to be retested either at lower concentrations or in different formulations. At smaller dosages, Permethrin has already shown side-effects no more severe than those of chlorphoxim. The most satisfactory larvicide in respect of its acceptability for the non-target fauna is Azamethiphos, which is unfortunaEely an organophosphorus compound. 10.3 Impact on non-ta' t aquatic fauna of permethr4l uled as an adulti cide During the adulticiding experiment on the Faya (see section 9.8), the contamination of the aquatic ecosystem by the vaporizing of permethrin was acceptable: no mortality was observed rmoog fish and mrcrocrustaceans; as regards the invertebrates, the marked fluctuations in discharge rate seem to have had a greater impact on the structure of the conmunities than the contamination of the hrater by the pesticide. No general conclusion can, however, be drar.'n from such an isolated experiment. 10.4 Analysis of data The data acquisition problems due to lack of staff, emphasized by the Ecological Group at its Septeober meeting in Bouak6, had been solved by October or November and the situation is now in hand. 1 1. Training of staff An entomologist was assigned to this work fu11 time, after the post had remained effectively vacant for a long time. An entomologist on the WHO project at Kaduna had a monthts specialized training at Ouagadougou, Bobo-Dioulasso and Bouak6- A Ugandan entomologis! completed a six-month training period in the OCP area in August. Two Guinean entomologists began in October an eight-week supplementary training Progralnme at Ouagadougou and Bouak6. Two Malian technicians began at IRTO a standard course of training as medical entomology technicians, at the same time as an OCP laboratory auxiliary in line for promotion. oCP/No .121 lvcu /84 page 23 As part of the continuing training prograrme, a timetable of refresher seminars was dravm up and updated courses and documents prepared. A one-month training period in ichthyology (10 daysr field work in Guinea and 20 days' theory at Ouagadougou) enabledaGuinean candidate hydrobiologist and two l"lalians to familiarize themselves with the techniques used for aquatic monitoring. A twoaonth training period has just, started for four invertebrate biologists (two from Guinea and two from Mali). 12. Participation in oeet ilcc UNDP-OMVS{CCGE-WHO meeting for the protection of Manantali, Dakar Meeting of National Onchocerciasis Corr-ittees, Lomr5, 6-8 June VBC/Industry meeting on insecticides, Geneva, 13-14 June CCClViking/OCP contractual meeting, ottawa OCP meeting of ttDevolution Group", Ouagadougou, 25-28 July OCP-VBC meeting on the development of IGRs, Geneva, 2-4 August OCP scientific review working groups, Geneva, 8-10 August and 16-18 August Meeting of the Ecol.ogical Group, Bouak6, 21-23 September Fourth meeting of OCP Expert Advisory Con*ittee, Bouakd, 26-30 September OCP scientific review working group, Geneva, 24-25 0ctober Meeting of Cottrmittee of Sponsoring Agencies, London, 26-28 October Several senior VCU staff also took part in the working and discussion group meetings that were health at Ouagadougou in connection with the long-term strategy, devolution, and the review of the scientific results of the Prograrme. 13. List of principal visitors '13.1 Consultants and tenporary advisers Ms P. Mr R. Dr R. Dr R. Dr A. Dr S. Mr H. Dr R. Dr A. Beyvin, France, VBC Secretariat Bigorne, France, hydrobiologist Cheke, United Kingdom, entomologist Cooter, United Kingdom, entomologist M. Denk6, Togo, parasitologist E. O. Meredith, United Kingdom, cytotaxonomist Orain, France, aerial operations Pa1, India, entonologist Renz, Federal Republic of Germany, entouologist 26 June - 17 July 13May-9June 17 l'[ay - 30 July 1-30 September 3-16 July 1 May - 15 October 50 days 9-31 May 16 July - 30 September oCP/No .121/vcul84 page 24 DrR DrS MrL Subra, France, entomologist Traor6, Upper Volta, entomologist Yam6ogo, Upper Volta, hydrobiologist 23 August - 28 October 1-30 June TFebruary-6Ju1y 8 August - 31 December 13.2 Other visitors Members of the Expert Advisory Cotnmittee and participants in the Cortmitteets fourth meeting (visit to Bouak6 sector) Members of the Ecological Group (visit to Bouak6 sector) Dr C. Be1lec, CEMV, Bouakri Dr F. G. Chary, Editor, Panorama du Mddecin Afrique, Paris Mr L. Charroeille, Chemist, Solvay-Biochem, Brussels Dr 0. W. Christensen, oCP Consultant, Geneva Mr ClaneE, Consultant Geographer, Ouagadougou Mr J.-P. Dailly, World Bank, Washington (visit to Lom6 Centre) Dr J. B. Davies, Liverpool School of Tropical Medicine Professor T. Diomandd, University of Abidjan Dr J. Duncan, TDRI, London (visit to Lom6 Centre) Dr N. G. Gratz, Director VBC, Geneva (visit to Bouak6) Mr J. P. Hervoudt, Consultant Geographer, Abidjan Dr R. Le Berre, vBC/ECv, Geneva (visit to Bouak6) Dr J. E. McMahon, Director, MRC Laboratory, Bo, Sierra Leone Dr J. Mouchet, OCP Consultant, Paris Mr F. Paris, Consultant GeograPher, Garoua (Cameroon) Dr A. Prost, World Bank, Washington Dr G. Qu6lennec, VBC/PDS, Geneva Mr Som6, Consultant Geographer, Ouagadougou Mr J. F. Walsh, OCP Consultant, Salford VCU also had the pleasure of helping to receive all the other visitors who came to Ouagadougou to look over the Prograrme in general. 14. List of documents prepared by VCU T616transmission des donnties hydrologiques dans 1a lutte contre Simulium damnosum. Report of an informal meeting held at Ouagadougou on 15 and 16 March 1983. Mimeographed document oCP/vcu/TEL/83.1, 65 pp. oCP/No .121 lvcu / 84 page 25 Annual meeting of hydrobiologists in charge of the aquatic monitoring of the rivers in the Qnchocerciasis Control Progranrne area, Ouagadougou, 6-8 April 1983. Unpublished report, 14 pp. Survol g6n6ra1 des activit6s de VCU depuis 1a troisiEme session du Comit6 Consultatif d'Experts (septembre 1982 - septembre 1983). Mimeographed document OCP/EAC.4.14 Evolution of the resistance situation and its impact on Ehe treatment strategy since September 1982. l{imeographed document OCP/EAC.4.3 Contribution to the transmission of Onchocerca volvulus by different species of the Simulium damnosum complex in the Prograrnme area. Mimeographed document OCP/EAC.4.4 OCP adulticiding research prograrrme. Mimeographed document OCP/EAC.4.5 Larvicide application equipment, development and application. Mimeographed document OCP(EAC.4.7 (Gradual setting up of a reduced entomotogical evaluation network in the central regions of the Prograrme.) Mimeographed docuoent OCP/EAC.4.8 Preparatory activities in the proposed western extension area. Mimeographed document ocP /EAC.4 .12 (Preliminary observations on the duration of larval life in Simulium daurosum s.1. obtained from three Ivory Coast rivers). Mimeographed document OCP/EAC.4.11 Note sur la contamination de ltaire trait6e dIOCP par les simulies de r6invasion pendant la saison des pluies de 1983. Document 0620/VCU, unpublished, 10 pp. S imul iun needs and progress in the application of biochemical techniques to the problem of vector identification. Unpublished VCU document, 16 pp. Utilisation des plaques dtaluminium dans 1e r6seau dt6valuation du Prograrrme de Lutte contre ltOnchocercose. Projet pilote. Consultantrs report, unpublished, 40 pp. R61e des diff6rents groupes cytotaxonomiques de Simulium daurosurc s.1. dans Ia transmission de lfonchocercose suivant les zones phytog6ographiques. R6sultats pr6liminaires. Unpublished VCU document, 12 pp. Prospects for the use of IGRs against Simulium damrosum larvae in West Africa VCU document, VBC neeting, Geneva, 3-4 August 1983 Guide pratique drutilisation des plaques dtaluminium destin6 aux chefs de secteurs et sous-secteurs du Prograuune. Consultantrs report, unpublished, 7 pp. L'hydrologie et 1a t6l6transmission dans le Progranrme de Lutte contre lrOnchocercose dans Ie Bassin de Ia Volta. 8u11. liaison CIEH, 54 (October 1983), 17-23 Experimentation with B.t. H-l4 aerial application equipment and with B.t. H-l4 formulations. Unpublished VCU ilocument, 12 pp. Adulticide research prograrme. Unpublished VCU document, 11 pp. Rapport dr6valuation des donnries dtop6rations a6riennes de 1a zone ouest. 5 pp., 1 map, 38 annexes, unpublished Consultancy report, ocP/No .121 IVCU 184 page 26 1 5 . Conclusions and future prospects The 1983 rainy season, which corresponds to the period covered by this rePort' \ras a relatively easy one for VCU, at least compared to the last few years. The logistic problems of larviciding r^rere very much simplified by the exceptionally severe drought that prevailed in the areas usually most difficult to protect. This relative lul1 allowed better advantage to be taken of the experience arduously acquired in previous years with regard to tactics and techniques of insecticide utilization. This combination of circumstances, together with an entomological situation that was particularly well in hand at the end of the dry season, enabled VCU to obtain overall results for the year which are among the best recorded since the start of the Progranme. gne of the major successes was the neutralization of the enormous blackfly reservoirs in southern Ivory CoasE, including a savanna-type population which, at the start of the year, had developed resistance to temephos. In contrast, that is to say when favourable conditions do not enable the logistic consequences of the resistance problem to be obviated in advance, this good entomological situation has brought into sharper relief the effects of reinvasion, which thus appeared this year as the principal cause of loca1 failures in the protection of valleys. In parallel rlith the treatment operations, significant Progress has been achieved in several spheres, including the development of new replacement insecticides, measurement of the susceptibility of vectors to insecticides, the epidemiological role of the various vector species, systems for application of biological larvicides, evaluation of a trapPing network, the practice of rotation of insecticides according to season and hydrological conditions' etc. VCU also took an active part, throughout this rainy season' in all the Programle's sEud.ies and efforts towards the working out of a long-term strategy' preparing for future devolution Eo the participating States, and couritting OCPrs scientific results to writing. Taking advantage of a dry season which already promises to be Particularly severe and should therefore a1low some respite to operational teams that have been working under constant pressure for some years past, these operations and studies will continue in the coming months' There is every reason to believe that Lhis 1983 rainy season, fruitful as iL has been in terms of entomological results, will at the same time have provided useful lessons on how to tackle in 19g4 a rainy season which, despite the difficulties it will entail for VCU' we must hope, for the sake of the agricultural populations of the Programe area, will be less arid than in 1 983. 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