Vector control activities from May 1997 to April 1998

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFzuCA Expert Advisory Committee Nineteenth session Ouagadougou. l-5 June 1998 Briefing session, 30 May 1998 OCP/EAC I 9/Briefing paper no2 OzuGINAL: FRENCH t I I VECTOR CONTROL ACTIVITIES FROM MAY 1997 TO APzuL 1998 l. Foreword In this report on the activities of the Vector Control Unit during the past 12 months we will draw a distinction between the "statutory" and the "specific" activities. By statutory activities we mean those "routine" activities carried out in the framework of the plan of action, of the Unit. By specific activities, we mean those "factual" activities planned during the year which have marked the period under review. 2. Statutory activities 2.1. Larvicidingcoverage In the original Programme area, aerial larviciding had definitively ceased in June 1997 on the Kankelaba in.Mali (a tributary of the Bagoe). But the aerial operations still go on the tributaries of the Oti in Togo (K6ran, Kara and M6) and ground larviciding operations continue on the Dienkoa in Burkina Faso. In the extension areas the first definitive cessation of larviciding occurred during the period, namely on the Marahou6, a river in the southern extension, C6te d'Ivoire, at the end of May 1997. No change in larviciding coverage had occurred in the other basins of the southem extension in Cdte d'Ivoire nor in those of the south-eastem extension area (South of Ghan4 South of Togo and South of Benin) and in Guinea. Ground larviciding on the Niger near Bamako and on is tributaries Fi6, Faya and Dylamba had continued to be carried out by the national team of Mali, with technical and financial support from OCP. In Sierra Leone, the continuing insecuriff was making highly unlikely any rapid resumption of larviciding in the northern part of the country. For the record, it must be recalled that no river of Sierra Leone had been treated since April 1994 (except for a few weeks in 1997). 2.2 Helicopter fleet and aerial operations During the period under review, the number of helicopters had varied from seven (May- December 1997) to four (April 1998). 1998 was the last year of a three-year contract signed for the third consecutive time between OCP and the "Evergreen Helicopter International" company. Negotiations undertaken during the past year by the legal office of WHO headquarters in Geneva and that company, in close collaboration with the Programme, had made it possible to reach an agreement for the last four years of the Programme. From a technical point of view, this new agreement had taken into account three basic considerations, namely: i) the definitive cessation of larviciding in C6te d'lvoire as of lst January 1999, ii) stabilisation of the larviciding coverage between 1999 and 2001, and iii) the significant reduction of aerial operations in2002. L 12.3 Insecticide rotation strategy The insecticide rotation strategy was aimed at preventing blackfly resistance and limiting the effect of larvicide treatment on the non-target aquatic fauna. As during previous years, the insecticides had been used taking into consideration the usual restrictions based on their toxicity, their cost-effectiveness as well as blackfly susceptibility levels to organophosphorous compounds in particular, especially temephos. With regard to Bacillus thuringiensis H-14 (B.r.H-14) formulations, the contract between OCP and the Abbott firm had ended in December 1997. Promising assays carried out during the past l2 months with another formulation of B.r.H-14 (Teknar @) were suggesting its possible use at discharges between 15 and 70 m3/sec because of its higher carrying-distance (almost double) and its lower operational dosage (three quarters of the current dosage). However, these two suppliers would be maintained in 1998 because of the difficulties experienced in controlling the fermentation parameters in the industrial production of constant quality B.t. H-14 batches. 2.4 Entomologicalevaluation Overall, entomological results had been satisfactory throughout the treated area during the period under review. Of 126 catching points monitored regularly, I l9 presented an Annual Transmission Potential incompatible with severe onchocercal ocular lesions (i.e. below 100). Of the remaining seven points, five presented an ATP below 200 (a relatively negligible transmission potential) whilst two of them located on the tributaries of the Oti showed a relatively high transmission potential (between 200 and 400). That basin was the subject of particular monitoring affention aimed at identifying the origin of the unsatisfactory results in order to take the appropriate corrective measures (see para.3) 2.5 Research activities Aside from the usual research activities, the period had been marked by the fine-tuning of the technique of pool screening of blackflies which consists in determining, through identification by DNA probes, the infectivity levels of the blackflies without having to resort to the classic dissection technique. The technique of identification by DNA microsatellite was also experimented. The staff of the molecular biology laboratory in Bouake was trained for that purpose and the technique would be applied in the very near future primarily in those areas where, for operational reasons, there is a need to better apprehend transmission conditions in a natural situation. 3. Special activities 3.1 Redeployment of activities in Sierra Leone To facilitate the management and conduct of onchocerciasis control operations in Sierra Leone, the decision had been made to close the operational base of Kabala in June 1998 and strengthen the sector and operational base of Makeni. However, the decision had not yet been implemented because of the events which occurred in these two bases in February 1998 (theft of materials and looting of the facilities). t-3- Due to the continuing insecurity, no resumption of larviciding or entomological evaluation was being considered for the moment. This period of forced inactivity would once again be taken advantage of to assess the entomo-epidemiological situation in the north of the country by means of a poster which would be presented at the briefing session of 30 May 1998. 3.2 Strengthening of activities in the Oti basin From the end of April to May 1997, anexceptionally high transmission was observed on the Keran, Kara and M6. To prevent any reoccurrence of such an outbreak of infective females, particular steps had been taken as early as June 1997 in order to better understand the causes of these results and institute appropriate corrective measures (intensification of ground control, "test" catches on neighbouring rivers, aerial prospections, intensification of therapeutical coverage, sociological surveys, etc.). In addition, and so as to avoid any reocculrence of any similar "outbreak" of infective females in April 1998, experimental aerial larviciding had been planned on the Oti for the month of April of this year in order to ascertain whether or not this watercourse was a source of blackfly reinvasion of the Keran, Kara and M6. A poster describing the results of these experimental treatments would be presented during the briefing session. 3.3 Specialization of the national teams in entomology During the National Coordinators' meeting in March l99T,arecommendation was made asking each country to identify a qualified medical entomologist to receive OCP sponsored advanced training in onchocerciasis and nuisance control. At the moment, almost all of the countries had designated their candidate and the training was scheduled to take place during the 1998 rainy season. A meeting between the medical entomologists and the national coordinators is planned at the end of the training period (probably in October) in order to discuss the major issues related to residual entomological activities (detection of infection in blackflies, post- control studies, nuisance control). A poster describing the status of the entomological detection of the infection in blackflies would be presented during the briefing session. ,