River blindness is a debilitating disease caused by a parasitic worm, and is the second leading cause of infectious blindness in the world. It is also called onchocerciasis, because the worm that causes the disease is Onchocerca volvulus. Infections are spread by a blackfly that lives near running water. 99% of the cases of this disease are in Africa.
As of 2008, about 18 million people were infected with river blindness disease, and approximately 300,000 were permanently blind from it. The disease is found in 30 countries of Africa, in Yemen, and in parts of Central and South America. Casual travelers are unlikely to contract this disease. Those who stay for longer, such as missionaries, Peace Corp volunteers, and adventure travelers can become infected with this parasite, however. There is no vaccine or preventative drug for river blindness.
People that live in agricultural villages near running water are at the greatest risk for infection. Infected people may not have symptoms. The symptoms of river blindness include one or more of several conditions. Infected individuals may have eye lesions, a skin rash, and possibly bumps under the skin. In the most serious cases, the eye lesions lead to blindness.
To become infected, a person must be bitten multiple times by infected blackflies. These insects inject microscopic worms called microfilariae into the person. The more of these worms that the person has, the worse his infection. Blindness is virtually always associated with severe cases of this disease. Infection with this parasite does not kill a person, but it is estimated to shorten his life by 13 years.
The flies mate in the area under the skin. An individual worm can live up to fifteen years. Each female worm can produce millions of microfilariae over her lifespan. The microfilariae can induce a strong immune response and inflammation, which has the ability to damage nearby tissue. They also cause a particularly strong response when they die.
Prevention efforts have included spraying fast-flowing rivers with insecticides that target the fly larvae. River blindness treatment involves use of 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 any offspring. In 1988, Merck & Co. started providing ivermectin for free through the Mectizan® Donation Program (MDP) in areas that have persistent problems with river blindness.
The MDP has been a success in treating river blindness. It was unclear, however, whether the disease could be eliminated. Research as of 2009 has indicated that bi-annual or annual treatment for 15-17 years has succeeded 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 was stopped for several years. This bodes well for river blindness elimination in other areas.