infectious diseases
Onchocerciasis (River Blindness)
Introduction
Onchocerciasis is a filarial nematode infection withOnchocerca volvulus. Blackflies (Simuliumspecies) are responsible for transmission. Symptoms are subcutaneous nodules, pruritus, dermatitis, adenopathy, atrophy and scarring of skin, and eye lesions that may lead to blindness. Diagnosis is by finding microfilariae in skin samples, the cornea, or the anterior chamber of the eye; identifying adult worms in subcutaneous nodules; or using polymerase chain reaction (PCR) to detect parasite DNA. Treatment is withivermectin. (See also Approach to Parasitic Infections and An estimated 21 million people are infected with onchocerciasis worldwide; about 14.6 million have skin disease and 1.15 million have visual impairment or loss. Onchocerciasis is the 2nd leading cause of infectious blindness worldwide (after Trachoma ). Onchocerciasis is most common in tropical and sub-Saharan regions of Africa. Small foci exist in Yemen and along the Venezuelan border with the Brazilian Amazon. Blindness due to onchocerciasis is fairly rare in the Americas; Colombia, Ecuador, Mexico, and Guatemala have been declared free of onchocerciasis by the World Health Organization (WHO). People who live or work near rapidly flowing streams or rivers are the most likely to be infected. In addition to residents, longterm travelers (eg, missionaries, aid workers, field researchers) are at risk. 