Prospects for the control of onchocerciasis in Africa with special reference to the Volta River basin.

Onchocerciasis is found in association with all the main river systems of northern tropical Africa, and there are endemic foci south of the Equator. Heavy and prolonged infection may cause blindness and intense pruritus. The vectors, Simulium damnosum and S. neavei, are also intolerable pests when they swarm. The disease and its vector together cause serious economic loss and are a main cause of the depopulation of river valleys in the savanna lands.The basin of the River Volta, in which the worst endemic area in the world is situated, is considered to be the most favourable area for a study of the problems involved in the large-scale control of onchocerciasis carried by S. damnosum. Mass treatment or prophylaxis are not practicable at present. The clinical condition progresses for many years in the absence of fresh infection, and drugs capable of mass application are needed. However, the first aim is to attack the larval stages of the vector with insecticides. DDT is ideal for this purpose in large, steadily flowing rivers, but a more suitable insecticide and formulation are needed for small, irregularly flowing streams.Research is needed into many aspects of the adult life of S. damnosum, including feeding and resting habits, dry season survival and flight range. One of the main practical problems is prevention of reinfestation of a treated river system.