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’s 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.
Read on to learn more about this condition.
There are different stages of onchocerciasis. In earlier stages, you may not have any symptoms. It can take up to a year for symptoms to appear and the infection to become 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
- light sensitivity
- loss of vision
In rare cases, you may also have swollen lymph glands.
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.
Adult worms can live for 10 to 15 years and may produce millions of microfilariae during that time. Microfilariae are baby or larval worms. Symptoms appear when microfilariae die, so symptoms can continue to worsen the longer you are infected. The most extreme, longest-lasting cases result in blindness.
You’re at increased risk for onchocerciasis if you live near fast-running streams or rivers in intertropical areas. That’s because black flies live and breed in these areas. Ninety percent of trusted sources 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.
There are several tests used to diagnose onchocerciasis. Usually, the first step is for a clinician to feel the skin to try to identify nodules. Your doctor will do a skin biopsy, known as a skin snip. During this procedure, they’ll remove a 2- to 5-milligram sample of the skin. The biopsy is then placed in a saline solution, which causes the larvae to emerge. Multiple snips, usually six, are taken from different parts of the body.
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 symptoms. There are two ways that clinicians may use DEC to test for onchocerciasis. One way is by giving you an oral dose of the medication. If you’re infected, this should cause severe itching within two hours. The other method involves putting DEC on a skin patch. That will cause localized itching and a rash in people with river blindness.
A more rarely used test is the nodulectomy. This test involves surgically removing a nodule and then examining it for worms. An enzyme-linked immunosorbent assay (ELISA) test can also be performed, but it requires expensive equipment.
Two newer tests, polymerase chain reaction (PCR) and rapid-format antibody card tests, show promise.
PCR is highly sensitive, so it only requires a small skin sample — about the size of a small scratch — to perform the test. It works by amplifying the DNA of the larvae. It’s sensitive enough that even very low-level infections can be detected. The drawback to this test is cost.
The rapid-format antibody card test requires a drop of blood on a specialized card. The card changes color if antibodies to the infection are detected. Because it requires minimal equipment, this test is very useful in the field, meaning you don’t need access to a lab. This type of test is being widely used and efforts are underway to standardize it.
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. It also doesn’t require refrigeration. It works by preventing the female blackflies from releasing the microfilariae.
Nodding disease, which is a rare form of epilepsy, has been associated with onchocerciasis. It’s relatively rare, affecting somewhere around 10,000 children in eastern Africa. Trials are being conducted to learn whether or not doxycycline could help reduce the neuroinflammation that occurs.
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). The 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. Those most at risk are residents of certain regions of Africa and Latin America. The best prevention is avoiding being bitten by blackflies. Wear long sleeves and pants during the day, and use insect repellant and wear permethrin-treated clothing. See a doctor if you suspect an infection so you can begin treatment before symptoms become severe.
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