Operations in western area: June 91- April 92

ONCEOOM,GilSIS CO}ITROL IBOGNAI'IME IN WEi[ AIN.ICA Ekpert Advisory Comittee Thlrteenth session om/EAclr/uierine paper no. 2 Oua.sadoleor. 8-12 Jnne 1992 hlefing sessior5 5 June 1992 OPERAIIONS IN WESIIERI ANEA Jrrne tl-Aprit !2 Since the last EAC session, the overall entooological situation in the l{estern Operational Area has been satisfactory. In the core area reinvasion was fully interrupted for the second consecutive year either in OSte d.flvoire or Ln !!a11. Transuission has been controlled in the rhole area. On the Bandiagara area (Mali) the second year of post treatuent evaluetion was conpleted with a very low level of transnission observed only in one point and it was far below the acceptable treshold. In the Banifing IV (MaIi ) , after suspension of treatnents a relatively high level of transmission was recorded. Aoong I total of 11 infective Iarvae collected fron flies and identified by DNA probes, aII turned to be 0. ochenqi. Further post-control studies wiII be carried out in 1992 and 1993 and aII L3s collected will be identified by DNA probe. Studies on nigrations wilI be conpleted in order to selectively treat nigrants with Mectizan. On the Upper white Bandana, ongoing post- control studies gave satisfactory results and the few infective larvae collected and identified at that time turned also to be 0. ochengi. A study of hunan nigrations in this basin will be carried out in order to assess the inportance of the migration phenonenon, the level of infection aoong nigrants and to deternine the probable origin of their infection. ln Guinea, entomological results have been excellent and no reinvasion at aII was observed. It appears now that levels of infection in flies after only 2 years of vector control are 10 to 15 times lower than in the core area after 5 years. This is likely due to the large-scale and very efficient Hectizan distribution over most of the area under vector control. As a result, very low levels of transnission were recorded even in case of local treatnentfailure with localized outbreaks of fIies. In Sierra Leone treatments did not resume in the southern part of the country. Transnission was successfully controlled in most of the area under vector control. Few points only located along the southern Iinit of the treated were recolonized by heavily infested forest flies coning froo untreated rivers. That apartr no reinvasion Has recorded due either to S. soubrense B or savana species. Transmission in northern Sierra Leone and Guinea can be successfully controlled whatever southern Sierra Leone is under vector control or not. Despite suspension of vector control, Ievels of transnission recorded in the South in 1991 were generally lower than in 1990 with vector control. This is probably because of the intensive Mectizan distribution carried out in f991 in Sierra Leone by National teaus, NCO's and health centers. -2 The cost of treatments (Iarvicides + flight hours) for the core area and Guinea were lower than in 1990 which were already lower than in lg$g. InSierra Leone it was much lower because of the suspension of the southern part ofthe country. The systematic rotational use of larvicides was successfully pursued.No operationnal difficulty resulted because of resistance. pyraclolos wag confirmed as the nost effective larvicide whereas phoxin turned to be difficultto apply and fairly unstable. tn the onset of the 1gg2 dry season sooe aeveretreatment failures were observed because of the Bt fornulation both in the corearea and in Guinea. Bt dosage had to be increaseTby 1.S to 2 x and naintainedin order to restore and keep in hand the entomological situation. [n bagins nottreated with Itlectizan significant levels of transnission where recorded(Sassandra and Baoule basins in core area) whereas no transnission was observedin treated areas (Niger basin in Guinea).