River blindness is caused by a parasitic worm transmitted by black flies and is the second leading cause of infectious blindness worldwide. It affects 18 million people, mostly in Africa, and there is no vaccine or preventive drug. Treatment involves using the drug ivermectin to kill the microfilariae. The Mectizan® Donation Program has been successful in treating the disease, and research has shown that semi-annual or annual treatment for 15-17 years can eliminate the spread of the disease.
River blindness is a debilitating disease caused by a parasitic worm and is the second leading cause of infectious blindness worldwide. It is also called onchocerciasis, because the worm that causes the disease is Onchocerca volvulus. Infections are transmitted by a black fly that lives near running water. 99% of cases of this disease are found in Africa.
As of 2008, approximately 18 million people were infected with river blindness and approximately 300,000 were permanently blind. The disease is found in 30 countries in Africa, Yemen and parts of Central and South America. Occasional travelers are unlikely to contract this disease. However, those who stay longer, such as missionaries, Peace Corp volunteers, and adventure travelers, can become infected with this parasite. There is no vaccine or preventive drug for river blindness.
People who live in farming villages near flowing water are at higher risk of infection. Infected people may have no symptoms. Symptoms of river blindness include one or more of several conditions. Infected individuals can have eye lesions, rashes, and possibly bumps under the skin. In severe cases, eye injuries lead to blindness.
To become infected, a person must be bitten several times by infected blackflies. These insects inject microscopic worms called microfilariae into people. The more of these worms the person has, the worse his infection is. Blindness is practically always associated with severe cases of this disease. Infection with this parasite does not kill a person, but it is estimated to shorten their life by 13 years.
Flies mate in the subcutaneous area. A single worm can live up to fifteen years. Each female worm can produce millions of microfilariae in her lifetime. Microfilariae can induce a strong immune response and inflammation, which has the ability to damage nearby tissue. They also elicit a particularly strong response when they die.
Prevention efforts have included spraying rivers with insecticides that target fly larvae. Treatment of onchocerciasis involves using the drug ivermectin, also known as Mectizan®, to treat entire communities. This drug kills the microfilariae, causing initial side effects, but curing the disease in the long term. The adult worm survives, but cannot produce offspring. In 1988, Merck & Co. began providing ivermectin free of charge through the Mectizan® Donation Program (MDP) to areas that have persistent river blindness problems.
MDP has been a success in the treatment of river blindness. It was unclear, however, whether the disease could be eradicated. Research from 2009 indicated that semi-annual or annual treatment for 15-17 years was successful in eliminating the spread of the disease in parts of Africa. Only a few individuals still had infections, and there was no subsequent transmission of the disease after treatment had been stopped for several years. This bodes well for the elimination of river blindness in other areas.
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