river blindness
Britannica Concise Encyclopedia:
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river blindness
Human disease caused by a filarial worm native to Africa but also found in parts of tropical America and transmitted by several blackflies. It is so called because the flies that transmit the disease breed on rivers and mostly affect riverine populations. Blindness is caused by dead microfilariaethe larvae that can be produced for some 1518 years by adult wormsinside the eye. River blindness is common in savannah areas of Africa and in Guatemala and Mexico. In 1987 the World Health Organization began to distribute the drug ivermectin (originally developed for use against livestock parasites), which eliminates the microfilariae, though it does not kill the adult parasite.
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river blindness or onchocerciasis, disease caused by the parasitic nematode worm Onchocerca volvulus. The worm larvae are transmitted by the bites of blackflies (genus Simulium) that live in fast moving streams. Inside the body the worms form disfiguring skin nodules, where they mate. Their tiny larvae, or microfilariae, migrate through the skin, causing severe itching. If the infection reaches the area of the eye, allergic reaction to the microfilariae can cause blindness.
Tests can now detect infestation before the disease has progressed, and the new drugs ivermectin, which kills the larvae, and amocarzine, which kills adult forms, have begun to help control the disease. Blackfly eradication programs have had limited success because the flies can quickly develop resistance to pesticides.
River blindness, which occurs primarily in Africa, Central and South America, and Yemen, affects an estimated 18 million people. In Africa, two strains have been identified, a savanna strain and a forest strain. The forest strain does not usually lead to blindness, but it does cause severe skin symptoms (lesions, itching, discoloration, change in texture) that can result in social ostracism.
American Heritage Stedman's Medical Dictionary:
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on·cho·cer·ci·a·sis
(ŏng'kō-sər-kī'ə-sĭs) or on·cho·cer·co·sis (-sər-kō'sĭs)
n.
n.
A disease occurring in tropical Africa and Central America, transmitted by black flies and caused by infestation with filariform nematodes of the genus Onchocerca, especially O. volvulus, and characterized by nodular swellings on the skin and lesions of the eyes. Also called river blindness, volvulosis.
Saunders Veterinary Dictionary:
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onchocercosis
The diseases caused by infection with the nematodes Onchocerca spp. The presence of large numbers of microfilariae in the skin is associated with a severe, summer dermatitis called also wahi, kasen in cattle and summer mange or allergic dermatitis in horses. See also sweet itch.
An association is suspected between periodic ophthalmia in horses and onchocerciasis because of the finding of microfilariae in the eye and because Onchocerca volvulus is a known cause of blindness in humans.
The adult worms cause little problem to the animals but the hides and carcasses are damaged and reduced in value. The relationship between the worms and the occurrence of fistulous withers, poll evil and tendonitis is unproven. The lesions in the aorta caused by O. armillata are often extensive but appear to cause little clinical disease.
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Britannica Concise Encyclopedia
Britannica Concise Encyclopedia. © 1994-2012 Encyclopædia Britannica, Inc. All rights reserved. Read more
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The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2012, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/.
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American Heritage Stedman's Medical Dictionary
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company.
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