Onchocerciasis – or 'river blindness' – is a parasitic disease caused by the filarial worm Onchocerca volvulus. It is transmitted through the bites of infected Simulium blackflies, which breed in fast-flowing streams and rivers.
Onchocerciasis is a major cause of blindness in many African countries. About half a million people are blind or visually impaired due to the disease. Onchocerciasis also causes ugly skin disease with depigmentation and severe unrelenting itching.
As a public health problem, the disease is most closely associated with sub-Saharan Africa, but it is also prevalent in Yemen and Latin America. In the past, fear of blindness led people to move away from the fertile river valleys in the African savannah, reducing agricultural productivity and increasing poverty.