A Study on the Anthropophilic Blackflies (Diptera: Simuliidae) in Gilgel Glllbe River Area (Sw Etillopia) With Reference to the Transmission of Onchocerciasis

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Addis Ababa University


Studies on the anthropophilic blackflies in the Gilgel Ghibe area with reference to the transmission of onchocerciasis were conducted between April 1994 and March 1995. The results of this study showed that onchocerciasis was of low endemicity in the area. Parasitologically positive skin snips were recorded for 17.1% of the persons examined. The prevalence of infection in males (19%) was higher than in females (14.9%). The geometric mean number of microfilariae per skin snip was 11.14, and was higher in males than in females. Clinical signs and symptoms were observed in 26.3% of the population examined- itching (18.4%), pigmentary changes (3.5%), itching with pigmentary changes (3.07%) and itching with papular rash (1.3%). The collection of biting flies at four selected sites revealed Simulium damnosurn complex to be the predominant anthropophilic species in the locality followed by S. ethiopiense which appeared in very small numbers.. Dissections of 6,483 S. damnoSum complex showed an average parous rilte of 74.7%. The parous rate was observed to vary between the four sites. Parous rates of 87.8%, 62.4%, 56.9% and 41.4% were recorded at sites I, 2, 3 and 4lespectively, suggesting a differential dispersal of parous and nulliparous flies. Of the total 4,844 parous flies dissected, 1.8% were harbouring L3 larvae morphologically indistinguishable from Q. volvulus. The average number of L3 Q. volvulus per fly was 5.1. The infection rate at the different sites was, 2.32% (Site 1 ), 0.75% (Site 2), 0.97% (Site 3) and 2.98% (Site 4). The annual biting rate (ABR), the annual infective biting rate (AIBR) and the annual transmission potential (A TP) was,24,928.75, 328.7 and 1,669.5 respectively. Of the total 5 specimens of-.S.. ethiopiense 60% (3) were parous and none of these were infected. The species plays little or no role in the transmission of onchocerciasis in the Gilgel Ghibe area.