Presentation of VCU activities in 1994-1995

tlnsr{K \\,ORLD I{EALTI I ORGANIZATION ORGANIZATION MONDIALE DE LA SANTE ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PRoGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST PRESENTATION OF VCU ACTIVITIES IN T994-1995 1. POINTS TO BE RETAINED IN THE EAC DOCUMENTS Among the reports particularly related to vector control (OCP/EAC 16.1, OCP/EAC 16.2 ancl OCP/EAC 16.6), some points, which we will not mention again in the rest of this document, should be retained: (1) Expansion of the Ecological Group's mandate to include the study of the inrpact of hunran resettlement on the aquatic environment (OCP(EAC 16.1). (2) C<lntinuation of the long-term evaluation of the impact of etofenprox (Vectron), permethrin, pyraclofos and carbosulfan (OCP/EAC 16.1). (3) Availability of the DNA-probe technique for the detection of blackfly infection by O. volwlus. What remains to be done now is to determine the modalities for its possible use in devolution activities (detection of recrudescence). (4) Cessation of post-control studies because of the generalization of ivermectin distribution (OCP/EAC 16.2). (5) Proposal to stop larviciding definitively at the end of 1996 on the Marahoue basin and on the lower Black Volta, larviciding being replaced by ivermectin distribution rhree to four times per year on the latter (OCP/EAC 16.2). (6) Addition of the Keran, Kara and Mo basins to the south-eastern extension because of the permanent infiltration of infective blackflies until the beginning of larviciding in February 1988 (OCP/EAC 16.2). (7) Continuation of research on the development of DNA-probes, in collaboration with Di Unnasch's laboratory: a technique for adult blackfly identification is practically operational (OCP/EAC 16.2). EXPERT ADVISORY COMMITTEE Sixteenth session Ouacndouqou. 5-o June laq5 ocP/EAC.l6.4 ORIGINAL: FRENCH 2(8) Proposal of a timetable up to the- yTlllOZ for the closure of the different vcu trases as larvicirling is definitively stopped (ocP/EAC 16.?). 2.OTHERACTIVITIESCARRIEDoUTDURINGTHEPERIoDUNDER CONSIDERATION 2.1,. l-arvicides As in 1993, the rainy season started late on all the river basins under larviciding' However, from Juli, heavy'and frequent rains led to a rapid and. exceptional rise in the water levels whicn firougt i uunut dislharges two to three times higher than those recorded in the previous y;. -6o*"qr"ntly, the-flood-subsidence period came several weeks late as welr as the ro*-,,nui", period whictr derayed up to the month of December in some basins in the western zone. In the eastern rrlne,many tributaries and subtributaries, which are usually untreated, were brougt t unoei iu*i.iaing. In the western zone, larviciding was interrupted in northeln Sierra ljone, most of the tirne on all the basins, because of the increasing insecurity. on the other basins in the western zone, the larviciding coverage remained significant up to mid-Aprit because of the late low-water period. - This resulted in a flight-hour and insecticide consumption slightly greater than,the estimates. However, this did not prevent it " ptunn"d definiiive cessition of larviciding at the-beginning of 1995 on the Baoule' the nugi. (with tt " .i..piion of the.KankelaUi), the Pampana, the Teye' the Kulpawn' the More, the Alibori ano'tt e Sota. with a view to a complete autonomy with effect from 1996 (reactivation of the Bamako operational base), Mali'inational teant is participating closely inlrorno larviciding of the Niger and its tributaries near Bamako' The same applies to t6e Dienkoa in Burkina Faso where the national team is fuily responsible for the ground larviciding with ocP technical and financial support. The principle of the insecticide rotation strates, .ai1ed at preventing possible blackfly ,"rirtun..i["no*"nu and limiting rhe effects of larviciding on the non-target fauna, has been the samJas in previous years lFigure 1). As in each year, the insecticides have been used by taking into account the'uJual reitrictions related to the toxicity of the larvicides, their costleffectiveness and levels of susceptibility of the blackflies, particularly to temephor, pho*i, and, to a lesser extent, Permethrin and pyraclofos' Despite the decreased permethrin susceptibilitf ou."*.d in'the areas where pyrethroids are used in agricultr.rre, the latest resulis obtained on the lower Mono antl the lower Oueme have removed the 6oubt concerning this insecticide which is still very effective' After the 1989 episode on the Marahoue, a dJcreas"Jrur..p,ibitiry to pyraclofos has been revealed on the Niger n"u, nun,oto. .ttttorgh it has not uft".t"diranimission, this phenomenon calls for caution, particularly as regard. grnrn.l iurviciding which is reputed to be favourable to the selection of resistant strains. 3Vectron has been used for the first time on the Sassandra, the Comoe, the lower Bandamaand the lower Black Voltq i.e., basins on which the use of temephos and phoxim is inadvisable or even forbidden. By authorizing the use of this seventh insecticide, the Ecological Group has, thereby, put an end to the search for new compounds and directed our activities towards the development of more effective Ee H-14 formulations, the preparation of recombinant strains or the search for new entomopathogenic species of Bacillus sp. The year 1995 saw the end of the contract with the company, Abbott, and its renewal for three years with the hope that a more effective oily formulation would be developed. This year, there have not been special problems with the operational batches of Vectobac except three containers which came in January 1993 and which, as regards efficacy, do not meet the contract's specifications. 2.2 Aerial operations As in every year, the aerial operations of the Kara and Odienne bases have been carried out without any major problem. The performance of the aerial spraying contractor has been satisfactory. The number of flight hours and of helicopters used in 1994 have conformed to the forecasts, i.e., 5,335 guaranteed hours, 713 additional hours and 97 helicopters/month, which, in terms of flight hours represents a decrease of some 107o compared to 1993. In fact, the precision of those forecasts is due to the fact that the increased workload related to the exceptional hydrological conditions has been made up for by the decrease in the activities in northern Sierra l-eone. The aerial contract between OCP and the aerial spraying contractor will end on 31 December 1995. The company has given us full satisfaction as regards the type of aircraft used and the spraying system as well as the experience of the pilots and mechartics and the seriousness of the company concerning the managemenl and nraintenance of the helicopters. 1996 will be the first year of the new aerial spraying contract. Planned to last three years, it rvill terminate at the end of 1998, i.e., at the end of the first year of the phasing-out period. The only notable change, compared to the previous contract, will be the presence in the Programme area of two spare helicopters instead of one and the possibiliry of having recourse to only four additional helicopters instead of five. Whichever company will be selected, the same quality of service as that provided by the previous company will be demanded, particularly as regards the spraying system and the automatic larviciding recording system (number of points, time, insecticide quantity used). In 1995, the total length of river likely to be treated (Fig.2) is 13,133 km. This maximal larviciding coverage is, of course, theoretical. Nevertheless, during the week of 18 to 24 July 1994 (period of rise in water levels and therefore of high larval productivity), a figure of 12,722 km of treated rivers (960/o of the maximal coverage) was recorded, nrobilizing nine out of the eleven helicopters under contract (Fig. 3). On the contrary, the u'eek from 3 to 9 April 1995 (lorv-water period and therefore of low larval productivity) saw the lorvest larviciding coverage (four larviciding helicopters) with 3,123 km of river treated, i.e.,24o/o of the maximal coverage (Figure 4). Two other weeks deserve to be mentioned, i.e., that from 2l to 27 November 1994, in the flood-subsidence period, duringwhich larval productivity was particularly high (71,472 km treated - Figure 5) and that fronr 19 to 25 Septernber 1994, in the high-water period which was calnrcr entonrologically (5,12tt km treated - Figure 6), during which larviciding was completely sirspended in the rvestern zone. 2.3 Entomological evaluaiion At presenl the entomological evaluation network comprises 146 catching points including 73 which are visiied every week (A points) and 73 others which are visited every 15 days (B points). In the dry season, transmission may be virtually interrupted. The periods most difficult to control remain the rise in water levels and, to a lesser extent, the flood-subsidence period during which larval productivity is intense and human/vector contact is high (land clearance in June-July and harvest at the end of the year. Only one infective female was caught in the whole Programme area during the week of 6 to 11 March 1995. On the other hand, transmission was relatively high from 1l to 16 July 1994 (44 infective females and 101 infective larvae). However, these figures, which could be considered as being equivalent to a quite exceptional transmission peak in 1994, represented, up to the end of the 1980s, almost the weekly mean calctlated for the whole year (a mean of 34 infective females with 109 infective larvae caught each week just for the year 1990). ' However, some reservations should be expressed on this comparison which does not take into consideration the fact that ivermectin coverage has been intensified from year to year and has finally been generalized, with effect from 1991/1992, in the whole of the basins under larviciding. Nevertheless, a comparison of the results, from 1991, calculated using the same number of catching points among the most representative ones (141 in all) clearly shows a rapid decrease in residual transmission, from 21 infective females and 58 infective larvae of Onchocerca sp. for the period of May 1991/April 1992 to six infective females and 18 infective larvae of Onchocerca sp. for the period of May D9a/April 1995 (Figure. 7). For the year 1994, the annual transmission potentials (ATPs) clearly show that residual transmission is mainly due to forest species (Fig. 8). If the transmission due to the savimna species alone is considered, out of 174 catching points monitored regularly, only four have an ATP above 100 and about 66Vo a zero savanna ATP (Fig. 9). The actual calculation of the ATP considers that the infection-carrying blackfly species determines the seriousness of the disease. However, it has now been demonstrated by the latest DNA results that savanna blackfly species could transmit forest parasites and vice versa. A new ATP has therefore been calculated which is bised solely on the taking into account of only infective larvae identified as savanna-strain Onchocerca volwlus. With this rnethod of calorlation, the transmission potential map (Fig. 10) is, with some two exceptions (Kaboua on the Okpara and Mbetekoukou on the Oueme), similar to that based on savanna blackfly identification. The present ATP calculation method therefore seems to reflect well the intensity and nature of transmission, especially since the gravity of onchocerciasis towards Kaboua and Mbetekoukou, which are in a region near the Nigerian border, seems to be far from having been demonstrated. 52.4 Research activities The results of the routine activities (insecticide susceptibility tests, quality control of operational batches, evaluation of new E,11, H-14 formulations, training activities, etc.) have enabled the officers in each zone to carry out their activities, as in each year, without major problems. The DNA-probe laboratory in Bouake has maintained its performance with iegard ro the identification of parasites collected in the Programme area. For the period ,nder consideratiorL 524 infective larvae of Onchocerca were identified including422 (80o/o) belonging to rhe Volvulus species. As in every year, since 1993, these results make it possidle to .orr".t rhi iiansmlssion potential, thereby contributing operatioirally, to a better management of vector control. The collaboration with Dr Unnasch is being continued and considerable progress has been made on many projects, particularly the heteroduplex technique based on the analysis of a segment of the mitochondrion DNA and allowing the establishment of a phylogenesis closely corresponding to that established by cytotaxonomy. 2.5 Conclusions During the period under consideration, the Vector Control Unit did not face real difficulties apart from the usual alarms related to decreases in insecticide susceptibility, which were quickly brought under control, delicate hydrological conditions and, during the harmattan period, massive blackfly population movements from onchocerciasis-freed zones and therefore, very luckily, free from any infection. However, special attention must be paid to the zones where larviciding has been (or will be) stopped definitively despite epidemiological resuls which are still not fully satisfactory (see OCP /EAC 16.2). In ad<Jition to an attentive epiclemiological surveillance in these basins, it should be seen to that the instructions concerning ivermectin distribution are strictly respected, with regard both to the frequenry of the treatments and to the treatment coverage. The real worry remains the problems of insecurity in Sierra lrone and its consequences on the Progralme, not only in that country but also in Guinea, Cdte d'lvoire and Mali (see the different scenarios envisage<i in the plan of operations for 1998-2002 - document OCP/EAC 16.5). Finally, a logical consequence of the gradual cessation of larviciding is the closure of entomological sdctors and subsectors. 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