Anthropophily of Simulium damnosum s.l. and its rôle as a vector of human onchocerciasis in the Yemen Arab Republic.

Immature stages of Simulium damnosum s.l. were collected in four of the main wadis (Surdud, Zabid, Rasyan, Ghayl) which drain westward to the Red Sea. The species was absent from the Wadi Tuban which flows to the south-east, but other black-fly species were found herein. For the first time it was shown that S. damnosum s.l. in the Yemen bites man, may ingest microfilariae of Onchocerca volvulus and can harbour filarial infections. Out of 303 flies which were caught on human bait in the Wadi Rasyan 33% were parous, four contained developing and three third-stage larvae (two of the flies had larvae in the head) indistinguishable from those of Onchocerca volvulus. The significance of these findings for the epidemiology of onchocerciasis and the possibility of vector control measures are discussed.