What is Onchocerciasis?

Onchocerciasis is commonly known as river blindness. It is caused by a parasite that is transmitted by black flies in sub-Saharan Africa, as well as in Yemen and some parts of Latin America. The flies live and reproduce close to rivers; most people must receive several bites for the parasite to become problematic.

When the flies bite infected humans, they pick up Onchocerca infective larvae. Later, they bite other humans and transmit the larvae, which mature into adult worms and live in nodules under the skin. Inside the body, these adult worms can live as long as 15 years. Their larvae may produce an immune response that causes the symptoms associated with onchocerciasis.

What are the Symptoms of Onchocerciasis?

Onchocerciasis causes rashes and skin discoloration, severe itching and an eye inflammation that sometimes results in blindness if not treated. When the larvae die inside the eye, the inflammation that the body mounts in response to the larvae can cause lesions on the cornea. The optic nerve can also swell. This can cause vision loss that is sometimes permanent.

In a few patients, the lymph glands swell, but this isn’t a common symptom.

Onchocerciasis Causes

Onchocerciasis, also known as River Blindness, is a disease caused by parasites that live in fast moving streams and rivers, mostly in tropical climates. The parasite is carried by a black fly called Onchocerca volvulus, and the disease is caused by repeated exposure to bites from these flies. When an infected fly bites the patient, a parasitic female worm can then lay thousands of larvae in the human host.

These parasites then move through the blood stream and typically migrate to the lymphatic and mucosal systems of the body. Humans are generally only infected with the parasite and develop Onchocerciasis after long exposure. A person traveling to areas where these black flies exist is at very small risk of infection unless he or she stays in the area more than three or four months.

How is Onchocerciasis Treated?

A medication called ivermectin effectively kills the Onchocerca larvae, so that they cannot cause skin irritations and blindness. Providing this medication for people in affected regions has helped to reduce the prevalence of the disease, as fewer people are carriers.

The ivermectin kills the larvae, but not the adult worm. Powerful antibiotics may be able to kill the adults if they are causing problems in the body.

People who are not infected should take preventative measures by using bug repellants and wearing long sleeves and pants to reduce black fly bites.

Onchocerciasis Prevention

The most obvious measure one can take to avoid developing River Blindness is to avoid those areas where the disease and the parasites are present. There are roughly 30 countries that struggle with large populations of infected people, mostly in Africa and Latin America, although there is some incidence of Onchocerciasis on the Arabian Peninsula (thought to be a result of the slave trade).

Currently, there is no vaccine for this disease, so it is very difficult to eradicate. If a person is in one of these regions for long periods of time, there are precautionary measures that he or she can take to avoid infection. Use of insect repellent, particularly DEET, during the day – which is when the flies are most active and likely to bite – is one of the most effective methods of prevention. Long sleeved shirts and long pants are also helpful, especially if they have been treated with permethrin. The medication ivermectin has been found to be very effective in controlling Onchocerciasis as well.

Last Reviewed:
October 10, 2016
Last Updated:
April 30, 2019