What is African River Blindness (Onchocerciasis)?
African River Blindness is an eye condition that can happen after being infected by a particular parasite. It is the second most common cause of infectious blindness in the world. People who are infected by this parasite usually have other symptoms before any blindness happens, especially itching and bumps in the skin. The parasite infection is called onchocerciasis.
What causes African River Blindness?
African River Blindness is caused by a nematode – a parasitic roundworm that only affects humans. It is spread through the bite of a blackfly (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 (the baby nematodes) 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 (called the cornea), the middle of the eye (including the trabecular meshwork – where the eye drains extra liquid to maintain proper pressure), and the back of the eye (the retina). As a result of the body’s reaction to the parasites, the delicate structures in the eyes are damaged, leading to blindness.
If the cornea is damaged, it can cause a scar, which can block vision. If the drainage system is damaged, it can cause pressure to build up in the eye and lead to glaucoma. If the retina is damaged, the eye cannot collect and send visual input to the brain properly.
It usually takes years for the initial onchocerciasis infection to cause blindness. In areas where the disease is most common–such as parts of Nigeria and Zaire around rivers where the blackfly lives–up to four out of five people will be infected. Average life expectancy can be up to 12 years less for people who are infected compared to people who are not infected.
Who is at risk for African River Blindness?
African River Blindness is most common in developing nations where the Simulium yahenese 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.
It is estimated that between 18 and 37 million people are infected, with up to 2 million people visually impaired or blind as a result of their infection.
African River Blindness Symptoms
The skin-related symptoms from onchocerciasis are found years before the development of eye problems. Skin changes can include bumps under the skin that can measure over an inch in size, skin irritation, intense itching, swelling, thinning and patches where the normal skin color is lost.
Eye symptoms include slow-onset decreased vision, eye redness, eye pain, light sensitivity, and clouding of the normally-clear front surface of the eye (the cornea). Many of these symptoms can also be caused by other conditions so a careful examination by an ophthalmologist is needed to make the correct diagnosis.
African River Blindness Diagnosis
Your ophthalmologist, with a team of other specialists (such as a dermatologist and an infectious disease doctor), can diagnose this condition based on a careful examination of your eyes and your body. The diagnosis can be confirmed by taking skin samples in suspected areas or by running blood tests. Other tests are currently being researched.
African River Blindness Treatment
Avoiding areas where the disease is common, using insect repellent and wearing appropriate clothing are all good ways to avoid being infected at all. If infected, early treatment of infection can prevent or diminish long-term problems. International programs such as the African Programme for Onchocerciasis Control (APOC) and the Onchocerciasis Control Programme (OCP) have reduced the numbers of people who are at risk for infection and have prevented blindness in over 200,000 people.
Once someone is confirmed to have an infection, anti-parasitic drugs can reduce the numbers of parasites found in the body. In 2015, William C. Campbell and Satoshi Ōmura won the Nobel Prize in medicine for their discovery of ivermectin, one of the most powerful anti-parasitic drugs used against onchocerciasis. This single discovery helped drastically cut the transmission rate of river blindness, and has cured Columbia and Ecuador of the disease.
More advanced onchocerciasis infections may require surgery to maintain or restore vision. These surgeries can include a corneal transplant (where the scarred cornea is replaced with a new healthy donor cornea); glaucoma surgeries to reduce the pressure in the eye; cataract removal (where the eye’s lens is removed and replaced with a new one); or retinal surgeries. In advanced cases, several parts of the eye can be affected at the same time. In these advanced cases, often there is no treatment possible and vision cannot be restored.