infections
Onchocerciasis
Introduction
Onchocerciasis is infection with the roundwormOnchocerca volvulus. It causes itching, a rash, sometimes with scarring, as well as eye symptoms that may lead to blindness. The infection is spread through the bite of female blackflies, which breed in streams. The infection may cause only intense itching but sometimes causes a rash, swollen lymph nodes, impaired vision, or complete blindness. Usually, doctors diagnose the infection by identifying an immature form of the worm in a skin sample. Administration ofivermectinonce or twice a year to people living in areas where the infection is common can control infection. If onchocerciasis causes symptoms, treatment is a single dose ofivermectin, which is repeated every 6 to 12 months until symptoms are gone. (See also Overview of Parasitic Infections and Worldwide, about 21 million people have onchocerciasis. About 14.6 million have skin disease, and 1.15 million have vision problems or blindness. Onchocerciasis is the second leading cause of infectious blindness worldwide, after Trachoma . Onchocerciasis is most common in tropical and southern (sub-Saharan) areas of Africa. It occasionally occurs in Yemen and in a small transmission zone in South America along the border of Venezuela and Brazil. 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 in these regions, such as missionaries, volunteers, or field researchers, are at risk. Onchocerciasis, or river blindness, is the second leading infectious cause of blindness worldwide. 