Progress in controlling the reinvasion of windborne vectors in the western area of the Onchocerciasis Control Programme in West Africa

1PROGRESS IN CONTROLLING THE REINV.ASION OF WINDBORNE VECTORS INTO THE WESTERN AREA OF THE ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA BY R.H.A BAKERf, p. cUrLLET$, A. S6K6T6Lrt, p. POUDIOUGOS, D. BOAKYE*, M. I{IILSONS AND Y. BISSAN* * 16 WaI lace Road , L,ondon N 1 zPG # Onchocerciasj.s Control. Programme, B.P. 549, OuagadouBou, Burkina Faso $ Dept. Medical Entomology, Liverpool SchooI of Tropical Medicine, Pembroke Place, Liverpool L3 SQA 21 INTRODUCTION Since vector control started in 1975, waves of Simuliun sirbanum and S. damnosum s.str., the principal vectors of severe blinding onchocerciasis in the African savannas, have reinvaded treated rivers inside the or:iginal boundaries of the Onchocerciasis Cont.rol Programme in West Africa (OCP) (Le Berre et al, 1979). L,&rviciding of potential source breeding sites has shown that these "savanna" species are capable of travelling and carrying Onchocerca infection for at least 500 km north-eastwards with the monsoon winds in t.he early rainy season (Garms et al, 1979; Magor & Rosenberg, 1980; Walsh et aI 1981; Johnson et aI 1985; Garms & Walsh, 1987). Annual Transmission Potentials (ATP), as defined by tIaIsh et al ( 19?8 ), in communities near the west,ern borders of the Programme have remained above tolerable levels and human infection indices have decreased much more slowly than in central areas where this reirrvasion has been controlled. Vector control has, therefore, been extended progressively westwards. Garms et aI ( 1979 ) documented how experimental treatments of the Marahou6 and Sassandra Basins in western Ivory Coast during 1977 and 1978 greatly redttced the reinvasion of the Leraba and Upper Bandama Basins i.n Lhe north-east of that country. In 1g7g, year-rouncl control. activi.ties were ext.ended to these river basins and substantial reductions in biting and Lransmission were recorded although t.he Marahou6 and Sassandra continued to be reinvaded (Walsh et al, 1981). rn 1984, the Programme embarked on a major western extension into Guinea, sierra Leone, western Mali, Senegal, and Gttinea-Bissatt. The fj.rst significant impact on reinvasion occurred in 1985 when the Upper Sassandra Basin in South-eastern Guinea was 3treat.ed for the first time. Biting and transmission flies in the Sassandra, Marahou6, Bandama and Leraba over 9O"/" (Baldry et al , 1985 ). by reinvading Basins fell by The Baoul6, Bago6 and Banifing tributaries of the Niger in South-eastern Mali and the extreme north-west of Ivory Coast have been treated since L977 but have proved to be more difficult to protect. The treatment of the Sankarani and Fi6, the easternmost river basins in Guinea, had only a marginal effect on reinvasion (Baker et aI, 1986). Further west, but still downwind and within 300 km of the reinvaded areas, the Milo, Niandan, Kouya, Mafou and Niger Rivers were found to contain very large S. sirbanum breeding sites and flies collected from these sites were similar in size to those invacling. Once the Inter-Tropical Convergence Zone (ITCZ) had been established to the north of the reinvasion zone, the periodicity of reinvasion could be related to changes in the height of these rivers - starting soon after their first rise at the end of t,he dry season and ending when they began to flood after the onset of the main rainy season. IL was concluded that these rivers must be the principal sources of the reinvading flies (Baker et aI, 1987 ). This paper describes progress in discovering the sources, elucidating the pathways and controlling reinvasion in the Western Area of the OCP dtrring 1987-89. Progress in containing the rei.nvasion of the Eastern area of the ocP has been presented by Garms et aI (1982), cheke & Garms (1983) and walsh et al (in prep.) 2 STUDY AREA The area covered by this study ( see Fig. 1 ) extends through 4five countries and includes the Upper Niger River Basin in Mali and Gttinea, the Sassandra, Bandama, Como6 and Black Volta River Basins in Ivory Coast and Burkina Faso together with coastal river basins in Sierra Leone such as the GreaL and Little Scarcies and Seli ( Rokel ). Descriptions of these areas have been given by Baldry et aI (1985) and Baker et al (1986 & 1987) and, for Sierra Leone, by Post & Crosskey ( 1985 ). 3 METHODS The OCP's gradual westward extension of vector control r^ras preceded by extensive helicopter and ground prospections to determine the geographical- and seasonal distribution of breeding sites for each vector species. A network of points (only a few of which are shown in fig. 1) for ll-hour day collections of biting flies was progressively established along all the main rivers and monitored by teams which had been selected and trained from national MinisLry of Health personnel. Flies were dissected to determine parit.y and infection forlowing a standard protocor (warsh et al, 1979 ) . Gauges were installed or recalibrated on all the main watercourses, the mosL representative being fitted with ArgosR beacons which can transmit river heights every 20 minutes to the aerial bases via satel I ite. cytotaxonomy of the rarval polytene chromosomes (vajime & Dunbar, 1975) is still the only unequivocal method of identifying savanna vectors but adult females could generally be distinguished from "forest" species of the S. damnosum s.l. comprex in this area by their pale wing tufts (Kurtak et al 1981), pale fore-coxae and short, pale, compressed antennae (Garms et aI, 1982, Baker et aI in prep. ). rn Sierra Leone, s. squamosum were distinguished by 5electrophoresis (Thomson, in preparation). Maps showing the dist,ribution of each cytospecies were prepared and compared to graphs illustrating the strength and periodicity of reinvasion in t,he areas under vector control. rn this wayr the critical river stretches requiring priority treatment to prevent reinvasion were select.ed. To minimise the costs of vector control, only river stretches with rapids colonised by the savanna vector spec'ies were subjected to weekly aerial larviciding. Kurtak et al (1987) have reviewed the insecticidesr application methods and sLrategies involved. One biological (BaciIIus thurinqiensis Hl4) and fottr chemical insecticides (temephos, chlorphoxim, permethrin, and Carbostrlfan) were carefully alternated in order to maintain effect ive control and minimise the development of resistance while preserving the ecological balance in the treated rivers. The insecticides were generarly appiied by hericopter, and, aL high discharges, a fixed-wing aircraft was used. In the Upper Sassandra Basin of South-eastern Guinea, where anti-invasion larviciding had been so successful (Baldry et al, 1985), the same treatment limits were maintained, enlarging as each large tributary began to flow and contracting with the disappearance of savanna species. As a result of the limited effects of vector control in the sankarani and Fi6 Basins in 1984 and 1985 (Baker et aI, 1986) and the discovery of very large savanna breeding sites along the lowland stretches of the other main rivers in the upper Niger Basin in East.ern Grrinea ( Baker et. aI , 1987 ) , control operations clearly had to be extended to these rivers. During t-986, B.t. H14 larviciding was carried out in the Sankarani Basin to contain insecticide 6resistance, while in the Upper Niger Basin, the network of capture points to monitor control became operational, base-line data were coll.ected ancl the river gauges installed and calibrated. A11 st.retches of rivers in the Upper Niger Basin harbouring savanna flies (see fig. 1) were included in anti-reinvasion treatment circuits from April - JuIy in 1987, 1988 and 1989. In Sierra Leone, the collection of baseline data, the installation of river gauges and t.he training of the National Team began in 1988, and these results were used to determine the river stretches requiring priority treat,ment when vector control was initiated in April 1989 (fig. 1). In or:der to evaluate the achievements of an anti-invasion r.ector control campaign, the source breeding sites of any flies still biting within the treated area must be interpreted from the vect.or monitoring data. The possibitity of local breeding within the treated area must first be excluded either directly from breeding site prospections or indirectly from the parous rates over 20% ntrlliparous rates usually implying a control failure. The existence of addi.tional reinvasion sources can be inferred when signific.ant numbers of flies with high parous rates are collected at capture points near the westward treatment Iimits. Movements of ttrese flies may be tracked north-eastward by comparing graphs of biting densities per day at each capture point on their path (Johnson et al, 1985). Our incomplete knowledge of the factors initiating and terminating such long-distance movements, coupled wi th uncertainty as to the times of day and height.s of travel in the air stream (reviewed by Garms & [,*Ialsh, 1987 ) make it dif f icull to back-track reinvasions accurately to their source and predict their strength from year to year.. Detailed interpretation was also Iimj.ted by the incompleteness of the meteorological data from Guinea ?and Sierra Leone. These difficulties were compounded in this study due t.o the limited sampling programme with captures at most points restricted to one day per week. Capture frequencies were increased aL strongly reirrvaded sites buL some points on the apparent reinvasion path, particularily those not situated close to large breeding sites, rarely recorded the passage of migrant fIies. 4 RESULTS 4.1 Reinvasion of Ivory Coast 1986-89 Table 1 shows that since 1985, the treatments of the Upper Sassandra in South-eastern Guinea have maintained their impact on biting and transmission during the critical ApriI-June reinvasion period with 75%-95% reductions in Monthly Biti.ng Rates (MBRs) and 95%-99% reducti.ons in Monthly Transmission Potentials (MTPs) compared to the same period in 1982-84, when the treatment strategy in the reinvaded zones eras most comparable. ATPs (fig. 2l were first reduced in 1979 when year-round vector control eras undertaken in the Marahou6 and Sassandra Basins and then when the Upper Sassandra in Gttinea was added in 1985. The community microfilarial load, the geometric mean number of microfilariae per skin snip in adtrl.ts of 20 years or older, for Massadougou is at last dropping rapidly (fig. 3), and is approaching the trend predicted by the mot'lel (Remme et aI , in press). 4.2 Reinvasion of South-Eastern MaIi 198?-88 4,2,1 Biting and Transmission in Guinea & Mali Vector control in both 1987 and 1988 greatly redtrced biting and 8transmission in Guinea at those points where collections were made in 1986 (Table 21, Over 80% reductions were recorded at T616 and Mor:igbedougou in the Sankarani and Milo Basins, and over 60% at Sansanbaya on the R. Niandan. Despite these reductions, considerable ntrmbers of parous flies were caught. At Sansanbaya an MBR of 24830 was obtained in May-JuIy 1986 but 7580 and 10440 were stiIl. recorded in 1987 and 1988. Table 3 shows that in Mali, the 1987-88 reinvasion, as represented by cumulative May-JuIy MBRs, constituted a 72% reduction at Madina Diassa but only a IO% reduction at Kankela and Madina, a 36% reduction at Mpiela and a 35% increase at Metela when compared Lo 1977-83 when no treatments were conducted in Guinea. However, estimates of the reductions in biting and transmission achieved by spraying sorlrce breeding sites can only be very approximate because MBRs and MTPs have varied considerably from year to year (fig. 4 and 5) and it has not been possible to predict the strength of the annual reinvasion. 4,2.2 Effectiveness of Treatments in Guinea & Mali Parous rates at capture points beside treated stretches in Guinea and Mali remained very high in both 198? and 1988. rn 198?, during the period when fljes were invading MaIi, however, some local breeding l^,as reported in several of the complex rapid systems on the R. Niandan and R. Niger in Guinea which had been treated with B.t. H14. Formulations of t,his insecticide have a relatively short carry and treatment failures can occur when complex rapid systems are treated for the first. time. With greater experience and more accuratel.y calibrated river gauges this probrem was largely eI iminatetl i.n 1988. 94.2,3 Sierra Leone Savanna Populations & Reinvasion of MaIi During 1988, the search for additional sources of reinvasion further upwind in Sierra Leone was intensified. Post & Crosskey ( 1985 ) showed that savanna vectors were practicatly Iimited to the extreme north of the country but in May 1988, S. sirbanum breeding populations were found in all the main river basins though northern rivers were more heavily colonised ( see fig 6 ). Biting savanna flies were recorded at all capLure points, with a maximum of 650 per day on the R. SeIi at Arfanya in late May. During June, S. soubrense B began to dominate in biting collections until, by the end of .IuIy, biting savanna flies were virtually restricted to the Little and Great Scarcies Basins on either side of the border with Guinea (fig 71. I{hen the 1988 mean daily biting rates per week at capture points in Sierra Leone, Guinea and MaIi are plotted on the same graph (Fig 8 & 9), a wave of savanna flies can be followed north-eastwards from Arfanya through Yalawa (101-150 km) on the R. Mafou, Kouya Laya on Lhe R. Kouya and Yradou on the R. Niandan (151-200 km)r Sansanbaya on the R. Niandan and Morigbedougou on the R. Milo (201-250 km)r T616 on the R. Dion (251-300 km) and reaching Madina in N.W. Ivory Coast (401-450 km), Madina Diassa (451-500 km) and Kankela in Mali (501-550 km) in calendar week 24-25, Another wave was observed two weeks later passing through Balandougou, Banfarala and Diaragbela on the R. Niger some 100 kms fttrther north. FIies were thus apparently taking 2-3 weeks to reach Mali from the Mafou and Niandan Basins in Guinea and 4-5 weeks t,o travel the approximately 500 km from Sierra Leone to MaIi, a rate of one day per l5-2O km. This is within the estimate of 7-35 km made by 10. Johnson et aI ( 1985 ) for migrating flies in fvory Coast and Burkina Faso. 4.3 Reinvasion of South-Eastern Mali 1989 4.3.1 Biting and Transmission in Sierra Leone, Guinea and MaIi Table 3 and figs 4 and 5 show that the principal points in MaIi and N.W. Ivory Coast were still reinvaded in 1989 despite the t.reatment of aIl known savanna breeding sites upwind. At Madina Diassa (maximum L45 flies per day per week), Kankela (maximum 91 per day perweek) and Mpiela (maximum 94 per day per week), significant numbers of parous invading flies were recorded. However, very few flies were caught. at Madina (maximum 31 per day per week, and a May-July MBR of 788) - the best result ever recorded. In 1989, May-Jul y MBRs were 65%-86% and MTPs 83%-95% less than means for 19?7-1983, before any control was trndertaken in the Western Extens ion. The 1989 treatments also further reduced biting and transmission in the Upper Niger Basin (Table 21, This effect was most not iceable aL Sansanbaya where the cumulative May-JuIy MBR of 2276 was 78% lower than that recorded in 1988 , 70"/o lower than 198? and 9l% lower than 1986. MBRs on the R. Niger erere reduced by over 80% compared to the 1987-8 mean and, aL all points where 1986 data were collected, MBRs in 1989 were aLso reduced by at leasL 80%. On the Kouya, Upper Niandan and Mafou, MBRs remained aL between 60%-70% of the 1987-88 mean. MTPs have followed the same trend. At Sansanbaya, the MTP of 11. 106 was 70% lower than 1988, 55% Iower than 1987 and 9I% Iower than 1986. Over 65% reductions compared to the 1987-8 mean were recorded in the Sankarani, MiIo, Niandan and Niger Basins but there was little or no change on the Kottya and Mafotr. In May, ivermectin, a microfilaricide potentially capable of reducing transmission by up to 75% in isolated endemic communities (Remme et aI, 1989)' was delivered to hyperendemic communities in the MiIo, Niandan, Mafou and Niger Basins but no consistent effect on vector infectivity was recorded. Vector control also greatly depressed biting and transmission rates in Northern Sierra Leone. At Arfanyal the May-July MBR dropped by 97% ( from 25420 to 680 - with forest vectors making up 27o/" of the residual MBR) and the MTP by 98o/" ( f rom 1810 to 33 ). Low savanna r.ector biting rates and high parous rates were observed aL al.I point.s except those in the Upper Great and Little Scarcies basins near or over the Guinea border. 4.3.2 Ef f ectiveness of Treatment in Sierra Leone, Guinea & t'lali Parous rates remained high at virtually alI capture points besides treated river stretches in Sierra Leone, Guinea and MaIi. However, some local breeding may have occurred for a short time in Mali near Madina Diassa because on the two days when the highest nrrmbers of f lies ( 238 and 200) r.rere caught, only 76% and 6?% were parous although by the following day the parous rate at reverted to 98%. This suggests that reinvasion at Madina Diassa was less important than the biting levels imply and that we do not need to search for such a major source of savanna flies to the south-w-est. Parous rates aL Kankela and Madina hrere very high throughout and these two points may beLLer reflect the reinvasion picture. lL, Savanna vector breeding was not, however, completely eliminated in Sierra Leone. This was again parLly due to difficulties in aPplying B.t H14 to complex breeding sites for the first time btrt mainly Lo the problems encountered in treating tributaries of the Great and Little Scarcies which, at a critical time, were dry near their confl.uence wil-h the main river but flowing productively ttpsLream. Biting rates on the Great Scarcies River at Badi Kanti increased r:apidly f rom week 23, weII before the river began to f low. Two weeks later, the R. Kilissi, a major tributary on the right bank in Guinea was found to be strongly positive for S. sirbanum and then included in the treatment circuit. However, catches at Badi Kanti peaked aL 230 per day and were clearly an important potential source of invading flies. 4.3.3 Sorrrces of Reinvasion in 1989 A graph of biting rates along the reinvasion axis for 1989 ( fig 10) is much less clear cut. In week 22 the situation looked excellent with about 10 flies per day at all points (25 at Sansanbaya). Then in week 23 and 24 daily biting trebled or quadrupled at Yalawa, Yradou, Kouya Laya and T616 though remaining stable at Sansanbaya and Morigbedougou. Such a rise could be correlated with the increases in MaIi during weeks 25 and 26 but why was this rise not detect,able at Sansanbaya and Morigbedougou - both points where reinvasion had been very important in previous years? An zrddjtional rise in weeks 27 and 28 can, however, be detected at all points on the Southern Guinea axis. Along t.he Niger Balanclougou in weeks river fIy numbers 25-27, peaking aL gradually increased at Balandougou r Banfarala and tt. Diaragabela in week 27, A second peak at Balandougou was observed in week 31. 5 DISCUSSION 5.1 fvory Coast Since treatments began in the Upper Sassandra Basin in Guinea, May-July MBRs in the Sassandra, Marahou6, Bandama and Leraba Basins in Ivory Coast have been maintained at 75% - 96% and MTPs at 95"/" 99% of pre-1985 levels. Epidemiological indices (fig. 3) are now falling rapidly and with ATPs below 100 since 1985 (fig 2l this Lrend should continue. Potential reinvasion sources still exist to the south-west of the fvory Coast reinvasion zone. Garms (1987) has collected adults and larvae of both savanna vector species fronr several rivers in Liberia. A large population of breeding and biting savanna flies (maximum 335 per day in late May 1988) was found on the R. Moa in south-eastern Sierra [,eone in both 1988 (fig. 6) and 1989. However, since biting rates and transmission potentials have now been maintained at low levels for five reinvasion seasons and epidemiological indices are rapidly improving, it would appear that reinvasion from Liberia or south-eastern Sierra Leone does not play an import.ant role in the control of onchocerciasis in Ivory Coast. 5.2 Mal i and North-western Ivory Coast In 1 989, for the first points were Ivory Coast consi stently low time, biting and transmission at all throughout the MaIi and North-western and over 65% Iess than recorded beforereinvasion zone 1qtr OCP began treating in Guinea. In previous years, the strength of reinvasion had varied unpredictably (fiS 1) with up to sixfold differences in bitirrg rates between the years. UntiI 198?, reinvasion biting rates had always been highest at Madina Diassa but in that. year 72% less Lhan the 1977-83 mean were caught. However, jn 198? the R. Baoul6 started to flow only on the 6th JuIy, six weeks Iater than usuaL. Capture points beside slow flowing river stretches rarely catch migrating flies and if, as seems Iikely, Lhese flies, which are believed to migrate gravid (Bellec, 1976), are attracted to the vicinity of rapids, then this could explain the low catch aL Madina Diassa in 1987. If years with unusually }ate flow by the capttrre points are excluded (together with Kankela in 1985 which may have been affected by treatments of the Sankarani Basin (Baker et al, 1986)), the 1989 reinvasion was lower than ever before at aII points. In 1989, cumulative May-July MTPs (fig. 5) were below 100 for the first time. Epidemiological indices, which have only been slowly decreasing in this area (cf fig. 3 for Kankel-a) shotrld now improve rapidl.y if this is maintained. 5.3 Sources of Reinvasion in 1989 The hey quest.ion would appear to be to determine the source of the flies invading Mali during the main peak which started in week 24 and was at a maximum 2-3 weeks later. If we accept that flies do take at least 4 weeks to travel the 500 kms from north-eastern Sierra Leone Lo Mali, then the flies breeding in the poorly-treated tributaries of the Great and LittIe Scarcies, 100-150 km further west, shorrld take even longer. This makes it unlikely that these flies, which first apppeared in week 23, r^rere the main contributors to Lhis invasion. 1'. The only alternative hypothesis is based on the increase in biting rates observed in the Mafou, Kouya, Upper Niandan and Dion basins during weeks 23-24 but. is rendered more problematic by the stability of the biting rates aL Sansanbaya and Morigbedougou during the same period. Could the occasional poorly treated breeding site in Sierra Leone and Guinea have been responsible for the 30-40 flies per day irr the southern part of the Upper Niger Basin and could these fli.es have produced 150 per day aL Madina Diassa? If the Madina Diassa peak is reduced because of the relatively low parous rate in week 26 and jf wind conditions may favour long distance movement on particular days, thus increasing densities in the reinvatled zones, we may have a partial explanation. There are certainly no other obvious potential source rivers. Breeding sites in the Upper Great and Little Scarcies were probably responsible for the wave of invading flies which passed throrrgh capture points in the Niger River in weeks 26-27 and mainLai.ned relat ivell' high bi ting rates in Mal i and North-western f vory Coast rrnti I week 34-35 . I.Iith the experience obtained in treating complex breeding sites and partially flowing rivers in Sierra Leone during 1989, future reinvasions of Guinea and MaIi should be further minimised. 6 ACKNOWLEDGEMENTS fn a programme of t,his scale it is obviously impossible to acknowledge aII the individuals who contributed to the work described above. Spec ial thanks are e.xtended to: Mr. I . Sesay, Entomologist of the Sierra Leone National Onchocerciasis Team and his staff; Messrs R. Lama, A. Sagno and Dr. Kaba, entomologists of rh the Guinea National Onchocerci.asis Team, Dr. A. Akpoboua, OCP Bouak6, Sect.or Chief , his Sub-Sector Chiefs and their staff , Messrs I. Diallo and Y. Di.arra, OCP Sub-sector Chiefs at Bamako and Bougouni, and their staff, Mr. M. Kassambara, OCP Bobo Dioulasso, and his staff; Mr. S. Dramane, Dr. K. Doucour6, Dr. L. To6, and Mr. B. Tele for detailed surveys in Sierra Leone; Ms. Madeleine Thomson for electrophoretic ident,ifications, Mr. A. Soumbey and Dr. S. Doumbia for data analysis; Dr. C. Back for comments on the manuscript.; Drs. G. De Sole , [i. Y. Dadz ie and J . Remme f or epidemiologica-1. information; Messrs A. Si-b and Y. Cotrlibaly for cytotaronomi.<' assi sLance, Mr. A. Belli and the administrative servit:es €or Iogistic support; the pilots of Viking and Evergreerr Helicopters and the OCP aerial operations staff. We at:knowledge the key roles played bf,Dr. B. Philippon and Dr. D. Qui1.l6r'616, Chiefs of the Vector Control Unit; Dr.D.A.T. BaldrS- and trlr'. P. Kabo16, Chiefs of Aerial Oper.ations; Dr. J. Grtrnewald, Research Coordinator; D.G Zerbo, Chief Entomological Eraluation and Dr. H. Agoua, Chief C:errtral Zone, Final. 11'we are gratefrrl t-o Dr. E.l'1 .Samba, Programme Director for his continuing encortragement and permission to publish. 7 RIiFERENCES Barker, R.H.A., Baldr.u*, D.,\.T., Boak.v-e, D. & hils luleasures ailued at controlling the invasion of Theobald s. l. ( Diptera: Simuliidae ) into the Cont.roI Pr:ogramme Area. I I I . Searches in th of Grrinea for addi tional sources of f Iies inr. Mal j . Tror.r. Pest Manaqement 33, 336-346. onr M. 1987. S imul i rrm damnosum Onchoce rc ias i s e Upper Niger Basin ading south-easLern 1?. Balier', R.H.A., Baldry, D.A.T., Pleszak, F.C., Boakye, D. & WiIson, M. 1986 Measures aimed aL controlling the invasion of Simulium damnosum Theobald s.I. (Diptera: Simuliidae) into the Onchocerciasis Control Programme Area. II. Experimental aerial larviciding in the Sankarani Basin of eastern Guinea in 1984 and 1985. Trop. Pest Management 32, 148-161. Baldr5', D.A.T., Zerbo, D.G., Baker, R.H.A., Walsh, J.F. & P1eszak, F.C. 1985 Measures aimed at controlling the invasion of Simulium damnosum Theobald s.1. (Diptera: Simuliidae) into the Onchocerciasis Control Programme Area. I. Experimental aerial larviciding in Lhe Upper Sassandra Basin of south-eastern Guinea in 1985. Trop. Pest Manaqement 31, 255-263. BeIIec, C. 1976 Captures d'adultes de Simulium damnosum Theobald, 1903 (Diptera, Simuliidae) A I'aide de plaqtres d'aluminium, en Cheke , R.A. flank of vectors. & Garms, R. 1983 the Onchocerciasis Phil. Trans. R. Af ri qrre de l.'Ouest. Cah. ORSTOM. 56r. Parasitol. 14, 209-ZLI . Entomol. med. Reinfestations of the southeastern ConLroI Programme Soc. Lond. B 302 area by windborne , 47r-484, species of the Simulium R. Soc. trop. Med. Hyq. Garms, R. 1987 Occtrrrence of the savanna damnosum r:omplex in Liberia. Trans. 81, 518. Garms, R., Cheke, R.A., Vajime, C.G. & occurence and movements of different damnosum complex in Togo and Benin. Sowah, S members 1 982 The the Simulium ZooL. 69, of Z, anAew. 19. 2t9-236 Garms, R. & Walsh, J.F. 1987 The migration and dispersal of black flies: Simulium damnosum s.I., the main vector of human onchocerciasis. Pp. 2Ol-214 in K.C. Kim & R.W. Merritt Eds., BIack FIies: Ecology, Population Management and Annotated WorId List, Pennsylvania State University, University Park & l,ondon. xv + 528 pp. Garms, R., talalsh, rei nvasion of river basin hry south-western J. F. & Davies, J. B the Onchocerciasis Simul irrm damnosum . 1979 Studies on the control Programme in the VoIta s.l. with emphasis on the Parasit. 30, 345-362 .areas. Troperrmed. Johnson, C.G., Walsh, J.F., Davies, J.B., CIark, S.J. & Perry, J.N 1985 The pal.tern and speed of displacement of females of Simtrlium rlamnosum Theobald s.l. (Di-pt,era: Simuliidae) across the Onchoceriasis Control Programme area of West Africa in 1977 and 1978. BulI. ent. Res. 75, 73-92 Kurtak, D. C. , Grtrnewald, J. & Baldry, D. A. T. population management of Simulium vectors Africa. Pp. 341-362 in K.C. Kim & R.W. Flies: Ecologyr Population Management and Pennsylvania State University, [Iniversity 528 pp. 1987 Chemical of onchocerciasis in Merritt Eds. , BIack Annotated World List, Park & London. xv + 1981 Wing tuft colours Simulium squamosum Kr-rrtak, D. C. , Raybotrl d, J. N. & Vaj ime, in the progeny of single individuals ( Enderlein ) . Trans. R. Soc. trop. C.G of Med. Hys. 75, L26, ??. Le Berre, R., Garms, R., Davies, J.B., WaIsh, J.F. & Philippon, B. 1979 Displacements of Simulium damnosum and strategy of control against onchocerciasis. PhiI. Trans. R. Soc. Lond. B 287, 27 7 -288 . Magor, J.f. & Rosenberg, L.J. 1980 Studies of winds and weather during migrations of Simulium damnosum Theobald (Diptera: Simuliidae), the vector of onchocerciasis in West Africa. Bul1. errt. Res. 70, 693-716. Post, R.J. & Crosskey, R.W. damnosum complex in Sierra 1985 The distribution of the Simulium Leone and its relation onchocerciasis. Ann. trop. Med. Parasit. 79, to 169-194. Remme, J., De Sole, G. & van Oortmarssen, G.J. The predicted and observed decl ine in onchocerciasis infection during L4 years of successful vec:tor control with reference to the reproductive I i fespan of Onchocerca press vol.vulus. BuII. trlld. HIth. Orq. in Remme, J., Baker, R.H.A., De SoIe, G., Dadzie, K.Y., Walsh, J.F., Adams, M.A., Alley, E.S. & Avissey, H.S.K. 1989 A community trial of ivermectin in the onchocerciasis focus of Asubende, Ghana. I. Effect on the microfilarial reservoir and the transmission of Onchocerca volvulus. Trop. med. Parasit. {0 Vajime, C.G. & Dunbar, R.W. 1975 Chromosomal identification of eight species of the subgenus Edwar sellum near and ( Diptera: including S imul i i.dae )SimuI itrm ( Edwardsell.um ) damnosum Theobald Z. Tropenmed. Parasit. 26, 111-138. 20 Wal. sh , J. F. , Dav ies , .I . B. & Garms , re invas ion of the Onchocerc i.asis damnostrm s.I . : the ef fects of an into sotrthern Ivory Coast during 32, 269-273, Walsh, J. F. , Davies, J. B. & Le Berre, aspects of the first five years of programme i n the Volt.a River basin. 328-34{. R. 1981 Further studies on the Control Programme by Simulium extension of control activities 1979. Tropenmed. Parasit. R. 1979. Entomological the Onchocerciasis Control Troperuued- Parasit. 30, R. 1978 effect of Simulium Trans. R. Soc. Walsh, J.F., Davies, J.B., Le Berre' R. & Garms, Standardisation of criteria for assessing the control in onchocerciasis control programmes. trop. Med. Hvq. 72,6?5-676. 2tr. FIGURES Fig. 1 The Study Area showing: Country boundaries ( +++++ 1 , the main rivers (thin lines), the river Iengths (at maximum) treated in 1989 (thick dashed Iines), and the capture points mentioned in the text (1 = Niamototrr t = Massadougour J = Kato, 4 = Gite 3, $ = Pont. Leraba, 6 = Badi Kanti, "i = Kaba Ferry, S = Musaiar 9 = Makpankaw, 10 = Arfanyar 11 = Yir:afiIaia, 12 = Yifin, 13 = Balandougou, 1-t = Banfarala, 15 = Diaragbela, 16 = Yalawar 17 = Kouya Laya, 18 = Yradou, 19 = Sansanbayar 20 = Morigbedougou, 2L = T616r 22 = Madinar 23 = Madina Diassa, 24 = Mpiela, 25 = Kankela, 26 = Metela). Fig. 2 The effect of treatments of the Marahou6 and Sassandra Basins followed by the Upper Sassandra in Guinea on Annual Transmission Potentials at four capture points in the Ivory Coas b re inrrasion zone Fig . 3 Epidem j.oIog ica.l trends in the re invasion zones Fig. 4 Ma"v- - July cumulative Monthly Biting Rates aL f ive capture poinLs in t.he MaIi/North-western Ivory Coast reinvasion zone from I977 -1989. Fig. 5 May - July cumulative Monthly Transmission Potentiats at five capture points in the MaIi/North-western fvory Coast reinvasion zone from 1977-1989. Fig. 6 Distrjbution of the Simulium damnosum s.I. complex in Leone in April-May 1988r &S identified by larval S ierra 22 cytotaxonomy. Fig. 7 Percentage of savanna biting six capture points in Sierra - oo I 988..J, in weekly catches at during calendar weeks 15 fI ies Leone Fig. 8 Fi g. 9 Three-dimensional rate per week at 1988. representation of the mean daily increasing distanees from Sierra Fig. l0 Three-dimensional representation of the mean daily rat.e per week aL increasing distances from Sierra I 989. Map situating the capture points (1 = Arfanyar I = Yalawa, 3 = Kouya Laya, 4 = Yradour 5 = Sansanbaya, 6 = Morigbedougou, 'l = T616, 8 = Madinar $ = Madina Diassa and 10 = Kankela) on Lhe reinvasion axis between Sierra Leone and Mali as used in Fig. 9 and Fig. 10. biting Leone in biting Leone in 2, TABI.,ES TabIe t (a) Cumulative April-June Monthly Biting Rates and (b) Cumulative Monthly Transmission Potentials in the Ivory Coast Reinvasion Zone 1982-89. Table 2 (a) Cumulative ApriI-JuIy Monthly Biting Rates and (b) Ctrmtrlative Monthly Transmission Potentials in the Upper Niger Basin in Guinea 1986-89. Table 3 (a) cumulative ApriI-JuIy Monthly Biting Rates and (b) Cumulative Monthly Transmission Potentials in the Mali and North-western fvory Coast reinvasion zone 1977-89. rr\tr()O o)r..-@lo@ o)ooroct) rr)@(DN@ tr)CDOOrst o@crrFr- rr-@O{@O(or-@lOr-r-FN NO@ON@$loNF- r-- C\l N ol $I@CDCD(',@FOO)Nf-Or.t(oFN(o@(r)r @cor.-or(f) r-@O)Ol loFcf)1ocf) FT cf)N C! t- F l()O@!+$o)t--@O)$<oNOOt-Ol FF ON\t@CDCOr\OI@lo olcoorN$ rolo N @orOrrO OO@FN @(\lr CtTCv)loFto rFO(OOO, (o O, t-. r\@$r-N @olOcOO)Cf)(orf(olr)lO l.- lr) C\l OI st(o(Y)F oI N C\t C! (r) o,r-@ONCoCOI-r\t@NCqr-C! rFF cr) f-@to ooolo,o o(otr)lo o N(o(o@tolo Ol-OrFCr) rF o@oo$ o FO)Ff\(o lOt-Fl-Cr) lOrNr a J H F z@@sto@t!@@rocf)F FCDFo(L z H@<oONFg,OFFTO@ A@st\tstF H =az frNro Fv JvOstcO F.f]8,zoocetrJO F O v c.) J =(,oulF vz=Yo(L Nlo v vOstco lfEOOcguJFOvcOJ =rr')oLUF z=too- z-l-oZ*truFoo(rf uJo o- IJJ E, za <@ult =rrt@ CD F Zst<r ut ol =CDo o) @(t f @ @ o, r- @ CD F @ @ o) to @ o, \t @ CD cf) @ Ct) N @ o, o5^ Fzc, HH OlJ-(L- [rJ(rO =zt-(Lo- o= U) tIJF E, oz H F H c0 J -Fzo = (6 (a) MONTHLY BITING RATES CAPTURE POINT & MAP NO. PRE- ALL UPPER NIGER BASIN TREATMENT TREATED 1986 1987 1988 1987-88 PERCENTAGE REDUCTION 1987-88 1989 1989AND AND AND 1986 1986 1987-88 SI ERRA LEONE AODED 1 989 TERE (21 ) 28097 3373 2647 MoRIGBEDoUGoU (20) 23675 4026 3315 SANSANBAYA (19) 24830 7579 10436 YRADoU (18) 3881 7424 KoUYA LAYA (17) 7471 8769 YALAWA (16) 6986 8489 DIARAGBELA (15) 5978 2320 BANFARALA (14) 8140 15945 BALANDoUGoU (13) 4955 8459 (b) MONTHLY TRANSMISSION POTENTIALS TERE (21 ) 559 1 16 14 MoRIGBEDoUGoU (20) 636 176 78 SANSANBAYA ( 19) r rOA 242 363 YRADoU (18) 205 154 KoUYALAYA(17) 204 71 YALAWA (16) 126 151 DIARAGBELA (15) gZO 102 BANFARALA (14) 420 347 BALANDoUGoU (13) 39 407 3010 367 1 9008 5653 81 20 7738 41 49 12043 6707 65 127 303 180 138 139 236 384 223 1 466 21 44 227 6 2262 2587 3069 470 716 1 336 89. 3 84.5 63. 7 88. 4 80. 0 7 4.1 94.8 90. I 90. I 98. 4 93. 6 90. 9 51.3 41 .6 7 4.7 60.0 68. 1 60. 3 88. 7 94.1 80. 1 I 41 106 23 93 133 14 0 69 86. 2 67. 7 65. 0 87 .2 32.4 4.0 94.1 100. 0 69. 1 (n C;qt !a t GI or F @ .o ct o o; ra) ol ";t ro ln ol (o N (o o oot o ol GI o o ra) (lt ";qt @j cl or @ F c, I .o N o a ts o(o (\a ro(I,@@F G) (aqt @ o F cl f N (r! o)(o N ro(o 6t @ @ F N e rat F G'('l F * rr} F C' *t o N .o oNF !t()(otN F @dl .o F .ltN !a Fo@@ F t .o(I' c o +,(,))o o e. o * ao !t o do + F or N Foo ct + rlo@ ao CIN@.oI (nq, ot N N o F .o GI ra/|{ $lF(ot o N ro o(o F o 1r| F o @ N ol N @ r.) t ro N (o N J lJl F UI o (a $t !? dt N N F @ G) !t$t N t6 rt(o .o $t F F(o (r o ! t or J t! Ho - an .o oN lo N (o o f qt N(rl o tt N N (o(r' a o (r' @ a @ 1rl @rt * |r) N J UJ - :a F !t o F N N @ @ otlN qt sl OI o @(o ot ra1 F lfl$l Fo (o() (o F(o (o or o dl Ho I - G) @ lo @ N *(D !a t 1.l At @ ao o @6 G'o or ao(o Cl 16N o oJ HF t!Foa o Hott H =o eF J -F o = a d) tat() o(o or(n t !t ta) N N(o $t Llo(D No ro (o Q (r) ra1 rlo N o (D .o(o (v) N Fo F rt rr) N @ or J lr, F tg I @ F F N(o ra tatt ro i ro C' F F F 6 F (l F() t F ol(, @ i ao @N cto !t o @(n o (r' o N Fo or 6 F !tt ro N J l! - Y (o(rl 6 N F Gtt (o N @ @(n F lrl ol @ N F ro F tal o ro N CI N !} F ts! @ (o @ c) $t o or @!t o(o(o F @!t F F (o o{ ot Ho I = G' @ F or @to !t tFN clo(o(o (t) o)(o t F(l G) o t @6 F F(D(o (D o rf,$t F 6ots o6too to(o ro N to ro N N Ho = o @ or (o ro @ rlo$l rr) C! @N o ra1 or q, ro !t (o(o(o Fo GI @('r 6 N @ ao (D i N !o t oo G' N !t o{ J l! Ho - N$t Ho - t!e.zoUOFFIIJZ rJllj <F2e<OGuil{ slcFHFoo3OGGo)t!r!t!Fe.FozltHuJF<Z=2Ft! c<f()uJl!d.(LeUO-F o.f e,HUluzFF<ZEeur<<-YFz<<urOEF e.GUrd,qtdtc,Fr =HZF. ttt @ z-ot <GFFuil!< -&uJo-e]F cHo)(o @=Fl =<z{G tr.t oz<(-o, <-l-Ftlt=< -<urar, eF E<ol(o@urF@ -z=tHI!F 2f=F <(,Fs)Bll<F - ur u.te. e.GF ('r cl q, @ F @ @ @ t.)6 t @ (oq, N @ C' o @ (D F @ F F F € F oG uoez Fo- o- o- af,l!F e o H F H @ J I F o = G oo I $ a a a ot =EG = tltl J . F o G t o o a C' a ta , a a reofr'tl3 I Ijr o o I 'tr I t og.t t t I E- UJ J a al I tI l1, re'ots il G E oa a taIt a a - i I = o s - b oo a at @ CO N @ (o @ lo @ t @ [, ,7" EE =oo.ctsa9fEEE3oo .L' (EFO a UJzoN zI U' z trE lIJ HEI -- .A. =(J .A =ioiIIJ HFbAo.\Jo6 -oo = az G,F J 3zz Doo =oo(v) fi$ta o= i (r, o@fr fi;_o ot uJ@J 9F 3fr@li lOlio c) o)t\ G'N I o -Eo Go GLttr(u oo(E o oU o) o .CoL(E =o o tr o E+,o oLF + o -+ T o _/t\ \ T \ <+--l 5 o \ o-+ + \. ooooo ot oo(r) oo!t oo to oo @ a (la G' o o c)N 'tv[N3lod NotsstutlsNvur lvnNNv D oEtr oLF E o aJ .9E oL o. ) o ol = €sGOo-YEF =Yl;lll: oN o F (o F rf F ELort.Fb o L o oa,FO rts o oo.E= o @ sf ot o @ UJzoN zIa = UJE ltl I!F =ooz UIEF J 9 CIoJ o =lU e o. UJ o F oNo$otOo(oot\ o(D o peol leuelllorc!1,\l rtllunnuoc o) @ @z@o =N@i @q) @ 5EIIJ o. .+ Y =@a oYx -G,:u fi+ N J UIFEH ooZPOA65 =o -rE - - =I =* = o:o o z o = II I C' @ oN @N NN oooooooooooooooooooooooooooooooooooooooo(osfNOO(o$(\lO@@$(\t NN616IFFFFF \ i' + x II G: q >( Y<t1 X >( i I x <X4 sugull p Xz o = o @ @ @ r\o (o @ lo @ tfo G'o N @ F @ o @ (r) N @ N N 1\ o) @o F INN o) o o.F = J =? t = zI CO z -J = Jdtll o. YX J UIF UJ = a t oo so z o = + oooooooooooooooooooooooooC)o(|OIFO@)@f\(Q|l)$(!)NF FFT-F X X X I o >o 6 ,ao sdll,ll 1,:.i.... lll rlllt E:. :I t I +a a o @ co Y at' t raar /AS c ttt + t o o .) raaa a o rocI o o C tao E o3(, a ((f, EtC 8 6 rrtt tt oat aa aII I attt EEi s, ot L PERCENT SAVANNA FLIES J ooI @oI @oI {oI ooI otoI soI o,oI No * J oIode a mi Eil8f, =o2fr 2E E=J!JrZ.' ,^rbYt-PF -l@ @ @ .Jgt J ol J{ J @ I I Itr t: @ 'rt .n1 1ll5NDt t;i:Jri(oxi riN == o 'nt =L1i r F=FH N o N o) N5 N Ol No N{ N @ N(o il1l ==xq!D 2Fx { +. r I Ir r + x.! + X + ! I i ..' --x tu + D , t , B .><". Xr- !. m +- a a t Im otr ta , 8I 3 J t ; m 2 m ! ! o t I E 5 I I a a o + ,t rl { .+t tI a j I l- Sqor.llc a ot , I o o .{ ! 6 tIt\oo 5 I aI o o MEAN DAILY BITING RATE PER WEEK +oo o,oo Noo J ooo an oC{ -ilz s@ fig =- NE x an .t{ J o J(o N c, N J NN N o) Ns N(,t N ol N{ N @ N(o o,o (., J o)N o) o) o)5 { mlrlxa ;i o J I J oro -t or .J tNoo No J tN(,r o N(,l .J I o)oo o,o J I(r) oto o, Ot J I5oo so J Isql o s(,r .J I OIoo (,t o -l I(,t Oto DISTANCE (KM) FROM SIERRA LEONE MEAN DAILY BITING RATE PER WEEK J(,l o J ooOlc)o = Ioz J(o @(o ooc{ -tntz oC z m z Loz x @ -l{ J o J(o N C) N J NN N o, N$ N(,l N o) N{ N @ N(o oto o, J o)N o) o) G's {IrIlnx an o-lo J ! J oro .J(,t J !Noo NoJ IN(,l o N ol J I o)oo o,o .J tq) oto (.)(,t J Isoo so J I$qt o $ Ul -lt C'loo ot C)J I(,l Oto DISTANCE (Iffi) FROM SIERRA LEONE