Onchocerciasis is an infection caused by a particular parasite. This infection is also called African river blindness. It is the second most common cause of infectious blindness in the world. People usually have symptoms like itching and bumps in the skin before any blindness happens.
What Causes Onchocerciasis?
A parasitic roundworm causes onchocerciasis. Infection with this roundworm only affects humans. It is spread through the bite of the Simulium yahenese blackfly. This blackfly is found only in certain areas in the world, near fast-flowing rivers and streams. Onchocerciasis cannot be passed from one person to another.
After a bite by an infected blackfly, the larvae enter the blood and circulate throughout the body. They settle under the skin and gather together, forming bumps. As the parasites mature, they migrate throughout the body and can spread to the eyes.
The parasites can enter all areas of the eye:
- the front of the eye (cornea)
- the middle of the eye, including the trabecular meshwork (the drainage system of the eye)
- the back of the eye (retina)
The body's reaction to the parasites damages the delicate structures in the eye. This leads to blindness.
Damage to the cornea can cause a scar that blocks vision. Damage to the eye's drainage system can cause pressure to build up in the eye and lead to glaucoma. If the retina is damaged, the eye cannot collect and send images to the brain properly.
In areas where the disease is most common, up to four out of five people will be infected. This includes parts of Nigeria and Zaire around rivers where the blackfly lives. It usually takes years for the infection to cause blindness. The average life expectancy can be up to 12 years less for people who have the infection.
Who Is at Risk for Onchocerciasis?
Onchocerciasis is most common in developing nations where this blackfly lives. Areas with higher rates of onchocerciasis include Western Africa, Latin America, and Yemen. In the United States and Europe, onchocerciasis is only found in people who have lived in these affected areas before.
An estimated 18 – 37 million people have onchocerciasis. Up to 2 million people are visually impaired or blind as a result of their infection.
The skin-related symptoms from onchocerciasis happen years before eye problems.
Skin changes can include:
- bumps under the skin that can measure over an inch in size
- skin irritation
- intense itching
- patches where the normal skin color is lost
Eye symptoms include:
Other conditions can cause many of these symptoms. A careful examination by an ophthalmologist is needed to make the correct diagnosis.
Your ophthalmologist, with a team of other specialists (such as a dermatologist and an infectious disease doctor), can diagnose this condition. Your doctors will carefully examine your eyes and your body. They can confirm if you have the infection with skin samples or blood tests.
Good ways to avoid getting the infection include:
- avoiding areas where the disease is common
- using insect repellent
- wearing appropriate clothing
If you get onchocerciasis, early treatment can prevent or reduce long-term problems. Programs like the African Programme for Onchocerciasis Control (APOC) and the Onchocerciasis Control Programme (OCP) have prevented blindness in over 200,000 people.
If you have the infection, anti-parasitic drugs can reduce the number of parasites in the body. William C. Campbell and Satoshi Ōmura won the Nobel Prize in medicine for their discovery of ivermectin. This is one of the most powerful anti-parasitic drugs used against onchocerciasis. This discovery helped cut the transmission rate and removed the infection from Colombia and Ecuador.
More advanced infections may need surgery to maintain or restore vision. These surgeries can include:
In advanced cases, the infection can affect several parts of the eye at the same time. In these cases, often no treatment is possible, and doctors cannot restore your vision.