Onchocerciasis is pronounced 'onk-oh-serk-eye-assis'.
Onchocerciasis is a parasitic vector-borne disease caused by a worm that affects the skin, lymph nodes and the eyes of infected people. It is also called river blindness. The WHO estimates that worldwide there are about 500,000 people who are blind due to onchocerciasis. The disease is caused by a tiny worm called Onchocerca volvulus (figure below), which is transmitted from person to person in the bite of blackflies.