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.
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.
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.