What is River Blindness?
An African Disease Involving a Parasite Transmitted by Biting Flies
What is river blindness?
River blindness is primarily an African disease, common in central Africa, especially in villages near rivers and streams. A parasitic disease, it is caused by a large tissue roundworm that spreads from person to person through the bites of blackflies. The association with rivers occurs because this is where blackflies breed—in rivers where the water flows quickly, the humidity is high, and there is lots of plant growth.
Though it probably originated in Africa, and remains a major health problem there, river blindness has spread to other parts of the world: Saudi Arabia, Yemen, Brazil, Columbia, Venezuela, Ecuador, Guatemala and Mexico. It is thought that slaves brought from Africa to Central and South America introduced the worm to those regions.
The scientific name of the parasitic worm that causes river blindness, or onchocerciasis, is Onchocerca volvulus. One of the most devastating human parasites, onchocerca doesn’t kill, but does damage over many years, causing discomfort, deformity, and blindness.
Symptoms of river blindness
A person with just a few Onchocerca volvulus worms may have no symptoms at all, but people living in places where many others have the worms and where blackflies are continually spreading it, will be continually re-exposed and will have a chronic and worsening illness. Most symptoms result from the body’s immune response to the microfilariae, the worms’ young, which move through the tissues under the skin and eventually die there. Symptoms begin three to fifteen months after infection:
- Nodules under the surface of the skin, typically holding two or more live adult worms producing young. In Africa, nodules usually form below the waist, while in Central and South America they are generally above the waist, frequently on the head. This is a result of different blackfly feeding patterns.
- An itchy skin rash, which can be severe and debilitating. The skin may also be hot, painful and swollen.
- Inflammation of the lymph nodes, which often contain many microfilariae.
- Over time, the skin becomes thickened, wrinkled, darkened or depigmented (bleached-looking), sometimes resulting in a leopard skin pattern. In Central America, thickened earlobes and facial skin is typical. The skin rash is ongoing.
- In Africa, a condition known as hanging groin often occurs, where sacs of tissue containing infected lymph nodes hang from the groin. Significant enlargement—elephantiasis—of the scrotum is not uncommon.
- Microfilariae invading the tissues at the back of the eye cause an immune response that destroys vision slowly, often rendering the victim blind by middle age. The risk of blindness is increased if nodules containing adult worms are located on the scalp.
Can river blindness be cured?
River blindness is one of the few human parasites that infects only people, which makes Onchocerca volvulus a good candidate for complete eradication if resources were made available. There are drugs against onchocerca; however, there’s no perfect cure yet:
- Some of the drugs are quite toxic and have serious side effects.
- The best drug, ivermectin, is active against microfilariae, but repeated doses are required to kill the adult worms.
- Drugs do not reverse skin damage, hanging groin, or blindness.
- Resistance to ivermectin is appearing: the drug isn’t killing the parasite like it used to.
- Because river blindness affects mostly poor rural people, it’s difficult to both fund and deliver treatment and control methods effectively.
More articles about river blindness:
Read about other African diseases:
Sources:
Diagnostic Medical Parasitology 3rd ed. Garcia, Lynn S. and David A. Bruckner. Washington: ASM Press, 1997.
Foundations of Parasitology 6th Ed. Roberts, Larry S. and John Janovy Jr. Boston: McGraw Hill, 2000.
