Where is onchocerciasis most prevalent? How is it transmitted?


Simulium species. Black fly caught in the act of biting one of the editors (JEF). Note the small size compared with the hair shafts. (Courtesy of James E. Fitzpatrick, MD.)
Fig. 33.3 Simulium species. Black fly caught in the act of biting one of the editors (JEF). Note the small size compared with the hair shafts. (Courtesy of James E. Fitzpatrick, MD.)
Onchocerciasis, a disease produced by the tissue nematode Onchocerca volvulus, affects millions of people in Africa and Central and South America. The infective larval forms are transmitted to humans through the bite of the black fly (Simulium) (Fig. 33-3). The common term for onchocerciasis, river blindness, takes its name from its feared complication and the fast-flowing rivers where the parasite and vectors are found.

Nguyen JC, Murphy ME, Nutman TB, et al: Cutaneous onchocerciasis in an American traveler, Int J Dermatol 44:125–128, 2005.