Onchocerciasis

Onchocerciasis (/ˈɒŋkɵsɜrˈsaɪ.əsɨs/ or /ˈɒŋkɵsɜrˈkaɪ.əsɨs/), also known as river blindness and Robles disease, is a parasitic disease caused by infection by Onchocerca volvulus, a nematode (roundworm). Onchocerciasis is second in the world only to trachoma as an infectious cause of blindness. It is not the nematode, but its endosymbiont, Wolbachia pipientis, that causes the severe inflammatory response that leaves many blind. The parasite is transmitted to humans through the bite of a black fly of the genus Simulium. The larval nematodes spread throughout the body. When the worms die, their Wolbachia symbionts are released, triggering a host immune system response that can cause severe itching, and can destroy optical tissue in the eye.