www.thelancet.com Published online January 17, 2018 http://dx.doi.org/10.1016/S0140-6736(18)30101-6 1 Onchocerciasis, which is a disease caused by the filarial worm Onchocerca volvulus, is transmitted from individual to individual by Simulium black flies that breed in fast flowing rivers. The millions of larvae (microfilariae) released by the adult parasites invade skin and eyes where they can ...