Loa loa: the African eye worm | video of worm being removed from eye
This filarial parasite is indigenous to Central and Western Africa especially in rain forest areas. In the Congo River basin, it is estimated that up to 90 per cent of inhabitants in some villages are infected with the parasite.
Loa loa is transmitted to people through the bite of a deer fly of the genus Chrysops. The fly ingests microfilariae from the blood of an infected host and develops into the infective stage within 12 days. Here they migrate to the proboscis of the fly and are transmitted to another person through a bite.
Chrysops species feed only during the daytime and the bite is quite painful. Primates can be a reservoir host.
The symptoms of loasis usually don’t appear for years after getting infected but have occurred as early as several months. The microfilariae (larvae) typically appear in the peripheral blood within 6 months.
The adult worms may grow up to 70 mm and can live in the host for 17 years, all the time producing microfilariae.