Man with river blindness being led by his daughter. This disease, also known as onchocerciasis, is caused by the larvae of the parasitic roundworm Onchocerca volvulus, which is transmitted to humans via the bites of Simulium sp. black flies. After transmission the parasite larvae develop into adults in the skin, causing nodules. The adults breed and produce many larvae that spread throughout the body, including to the eyes. When the larvae die they produce a strong immune reaction that causes inflammation. It is this inflammation that causes blindness. Photographed in Garbabi, Nigeria.