This is an insect-borne disease caused by a parasite Onchocerca volvulus and transmitted by black flies of the species Simulium damnosum.
The disease spreads from person to person by the bite of a blackfly. Also called River Blindness because the transmission is most intense in remote African rural agricultural villages, located near rapidly flowing streams.
Within the human body, the adult female worm (macrofilaria) produces thousands of baby or larval worms (microfilariae) which migrate in the skin and the eye.
Persons with heavy infections will usually have one or more of the three conditions; derma titis, eye lesions, and/or subcutaneous nodules. Onchocerciasis is a major cause of blindness in many African countries.
The World Health Organization’s (WHO) ex- pert committee on onchocerciasis estimates the global prevalence is 17.7 million, of whom about 270,000 are blind and another 500,000 have visual impairment.
About 99% of infected persons are in Africa; the remainder is in Yemen and six countries in the Americas.
In some West African communities, about 50% of men over the age of 40 years had been blinded by the disease. Causing people to flee the fertile river valleys and settle in less productive upland country. Hence the annual economic losses were estimated, in the 1970s, at US$ 30 million.
Onchocerciasis is commonly treated with an oral medicine called Ivermectin.