Onchocerciasis

What is onchocerciasis?

Onchocerciasis, also known as river blindness, is a disease that affects the skin and eyes. It’s caused by the worm Onchocerca volvulus. Onchocerca volvulus is a parasite. It is spread to humans and livestock through the bite of a type of blackfly from the genus Simulium. This type of blackfly is found near rivers and streams. That’s where the name “river blindness” comes from.

What are the risk factors associated with river blindness?

You’re at increased risk for onchocerciasis if you live near fast-running streams or rivers in intertropical areas. That’s because blackflies live and breed in these areas. Ninety percent of cases are in Africa, but cases have also been identified in Yemen and in six countries in Latin America. It’s unusual for casual travelers to contract the disease because repeated bites are necessary for the infection to be transmitted. Residents, volunteers, and missionaries in areas of Africa are at the greatest risk.

What are the symptoms of onchocerciasis?

Symptoms of river blindness depend on the stage of infection. Symptoms of earlier stages may not be apparent. Once the infection becomes severe, symptoms may include: skin rashes, extreme itching, bumps under the skin, loss of skin elasticity, which can make skin appear thin and brittle, itching of the eyes, changes to skin pigmentation, enlarged groin, cataracts, loss of vision and light sensitivity.

You can develop river blindness if you’re bitten repeatedly by infected female blackflies. The blackfly passes the larvae of the worm Onchocercidae through the bite. The larvae move to the subcutaneous tissue of your skin, and mature into adult worms over 6 to 12 months. The cycle repeats when a female blackfly bites a person infected with onchocerciasis and ingests the parasite.

How can it be diagnosed?

To diagnose onchocerciasis, skin snips are taken from nodules and placed in saline solutions which causes larvae to emerge. An alternative test is called the Mazzotti test. This test is a skin patch test using the drug diethylcarbamazine (DEC). DEC causes the microfilariae to die rapidly, which can lead to severe itching if microflilariae are present. The most widely used treatment for onchocerciasis is ivermectin (Stromectol). It’s considered safe for most people and only has to be taken once or twice a year to be effective.

Several programs have improved the outlook for onchocerciasis. The African Programme for Onchocerciasis Control, in operation since 1995, established community-directed treatment with ivermectin (CDTi). Elimination of the disease is in reach for the countries where the program has been operating. There is currently no vaccine to prevent onchocerciasis. For most people, the risk of contracting onchocerciasis is low.