River blindness is caused by a parasitic worm that lives for up to 14 years inside the human body. This disease is called river blindness because the black fly vector lives in fertile areas near rivers. Each adult female worm produces millions of larvae that migrate throughout the body and cause serious visual impairment and sometimes blindness, rashes, lesions, intense itching, depigmentation of the skin, elephantiasis, and general debilitation. The disease shows symptoms one to three years after the infectious larvae enter the body.
The parasite is carried by the black fly, which lays its eggs in the water of fast-flowing rivers. Adults emerge after 8 to 12 days and live for up to four weeks. The female black fly ingests the larvae if she bites an infected person. She can spread the parasite when she bites other people afterward.
In 1987, Merck & Co., Inc., the manufacturer of ivermectin, pledged to provide the drug free-of-charge for as long as necessary to overcome river blindness as a public health problem. It established a donation program that works with the World Health Organization, health ministries, and nongovernmental organizations. Between 1987 and the end of 1996, more than 65 million doses of the drug had been donated for distribution.
A total of 18 million people are infected; 99 percent of them are in Africa. Of those infected, more than 6.5 million suffer from severe itching or dermatitis and 270,000 are blind.
The development of a drug called ivermectin in the 1980s was the first time there was a safe, effective drug that could improve symptoms and decrease the chances of disease transmission.
It turns out that a single dose of ivermectin once a year is all that is needed!