Expert Advisory Committee: fourteenth session: Ouagadougou, 7-11 June 1993: briefing session, 5 June 1993: vector control results in eastern zone from June 1992 to may 1993

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA Expert Advisory Committee Fourteenth session Ouaqadoueou. 7-ll June 1993 Briefing session, 5 June 1993 OCP/EACl4/Briefing paper no 7 ORIGTNAL: FRENCH YECTOR CONTROL RESULTS IN EASTERN ZONE FROM JUNE 1992TO MAY 1993 l. The season : Rainfall/Hydrology In 1992 the rains were late in the whole of the Eastern Zone, and were relatively low compared to those of 1991. The quantity of rains were lower in certain cases, than those of 1990 particularly at the southern stations. The rain gauge data obtained this year were l57o to 500/0 lower than those of I991. The southern regions especially those of the south-east, were those strongly hit by the drought contrary to l99l when they were the wettest. Effects of the rainfall deficit. Apart from the late flow observed on the rivers as compared to 1991, the discharges were lower than those of the previous years. The values obtained, in the majority of cases, did not reach half the value and in some cases a third of those obtained in 1991. The dry season of 1993 was classical but a bit drier than the normal type without any particular incident. 2. Larvicide coverage (treated rivers) ln 1992, the larvicide coverage was -area wise- almost the same as in l99l and will be the same in 1993. Treatment cessation due to good epidemiological results was carried out on the following rivers: The Upper Nzi upstream of the Sepie outfall, the Oti itself (treated only during the first quarter of the year), as well as the upper Pendjari and the Mekrou. The latter was however subjected to treatment again in week 33 when the results of the post-control studies were found to be unsatisfactory. 3. Use of larvicides/insecticides rotations The insecticide rotation was carried out successfully in the classical manner, namely taking into consideration two factors such as discharges and Simulium species' susceptibility to the different products. The important facts concerning the use of the larvicides are the following: An increase in the application of the organophosphates especially Abate in the White Volta and the Asukawkaw basins, was due to the return of normal susceptibility to the product. The much more important use of ovraclofos essentially as insecticide of attack during the period of recolonization, higher and lower discharge conditions. OCP/EACl /Briefing paper no 7 Page 2 The quantities of products used in 1992 were different from those used in 1991, in terms of insecticides family, because: - First of all, the season's poor hydrological situation (lower discharges of between 250lo to 600/0) brought about higher consumption of B.t. H-14 and Secondly the increased use of pyraclofos brought about a decrease in the use of more toxic insecticides such as permethrine and carbosulfan. 4. Global entomological results The simulium population densities in 1992 were very much lower than those of l99l in the whole operational area. The problems linked to the zone's borders were much less important than in the previous year, especially along the Nigeria frontier where the classic infiltration of S. soubrense was very weak. Locally, in the extension zones, and other places like those fomerly reinvaded from the above mentioned zones, the results were satisfactory. 5. Onchocerca transmission Concerning onchocerca transmission the results in 1992 were among the best ever obtained in the Eastern Zone. Decreases in transmission were obtained at foci like Asubende (ATP of I l9 compared to243 and 589 in l99l and 1990 respectively). Nakong on the Sissili had zero ATP. The same is true of residually reinvaded foci like the basins of the upper Keran and Kara. These good results can be attributed to a better larvicide application coverage on the one hand, and the intensification of ivermectin distribution on the other. Apart from the above good results, important seasonal transmissions affected the zone's border like the lower Oueme and the Okpara as well as the hilly areas in the Volta Region and the South-West of Togo. These transmissions can be attributed to forest species of the simulium fly. 6. Results of special studies As in 1991, special studies were undertaken during the 1992 campaign, in the following fields: The second consecutive year study of the infiltration movements of S. soubrense and its impact on transmission in the OCP area. The vector movements at the beginning of the dry season from non-treated area to the treated zones. - The possibility of treating the Sota basin manually during the dry season. Posters shall be presented on these studies.