an insidious non:killing parasitic vector-borne disease of public health significance, caused by the filarial roundworm Onchocerca volvulus (Leuckart, 1893), which is transmitted from person to person through repeated bites by several bloodsucking antropophilic black fly species. Man is the definitive host of O. volvulus and black flies (all of them belonging to Simulium genus) are its only natural intermediate hosts and vectors. The parasite is maintained entirely by inter: human transmission through the black fly intermediate host. There are no animal reservoirs of the parasite, human onchocerciasis is not a zoonosis. Human onchocerciasis is also called River Blindness because the black fly species that transmit the parasite breeds in rapidly flowing rivers and streams and because the infection can cause irreversible blindness.