ANTHROPOPHILIC BLACKFLIES (DIPTERA, SIMULIIDAE) AND ONCHOCERCIASIS TRANSMISSION IN SOUTHWEST ETHIOPIA

From May 1984 to May 1985, the transmission of onchocerciasis by black flies (Dipteria: Simuliidae) was studied around Gilgel Ghibe and Gojeb rivers in southwest Ethiopia. The predominant anthropophilic species of Simulium at both localities were S.(Edwardsellum) damnosum sensu la to and S.(Lewisellum) ethiopiense. Some S.(Anasolen) dentulosum also l anded on human bait at Gilgel Ghibe river. Dissections of S.damnosum f rom Gilgel Ghibe and Gojeb revealed mean parous rates of 92% (n = 18,2 91) and 84% (n = 9530), respectively. S.ethiopiense from Gilgel Ghibe and Gojeb showed mean parous rates of 53% (n = 322) and 93% (n = 14), respectively. Of the parous S.damnosum, 1.3% at Gilgel Ghibe and 0.5% at Gojeb harboured infective third-stage larvae (L3) of Onchocerca vol vulus (or morphologically indistinguishable from it). Unknown filariae of animal origin, indicative of zoophily, were found in 0.3% and 0.7% of Simulium damnosum complex females from Gilgel Ghibe and Gojeb, res pectively. S.ethiopiense harboured developing (L(1)) larvae only, with 7.7% infection rate in both localities. In contrast, S.dentulosum did not harbour any filaria larvae. The annual infective biting rate (AIB R) and transmission potential (ATP) of the S.damnosum complex at Gilge l Ghibe river were 858 and 5478, respectively. The AIBR and ATP of S.d amnosum s.l. at Gojeb river were 519.5 and 1963, respectively. These r esults emphasize the predominant role of the S.damnosum complex in the transmission of O.volvulus in southwest Ethiopia.