What Is Onchocerciasis, Also Called 'River Blindness'? Symptoms And Causes

Onchocerciasis, also known as river blindness, is a skin and eye disease. It is caused by the parasitic worm Onchocerca volvulus, a type of blackfly from the genus Simulium that transmits the disease to humans and livestock through bites. This type of blackfly is commonly found near rivers and streams. Hence, the name "river blindness".

The Onchocerciasis Control Programme (OCP) successfully controlled onchocerciasis in West Africa between 1974 and 2002 by spraying insecticides against blackfly larvae (vector control) by helicopters and planes. It was later supplemented by large-scale distribution of ivermectin in 1989 [1].

More than 99 per cent of infected individuals reside in 31 African countries. It is also present in Latin America and Yemen.

What Are The Symptoms Of River Blindness?

Onchocerciasis is a disease of the eye and skin. Symptoms are caused by the microfilariae, which move around the human body in the subcutaneous tissue and incite intense inflammation when they die [2][3].

There are several stages of onchocerciasis. There may not be any symptoms in the early stages. The symptoms and the infection may take up to a year to appear.

When the infection becomes severe, the following symptoms may appear:

• Rashes on the skin
• Swollen lymph glands (rare) [4]
• Severe itching
• Bumps under the skin
• Lack of elasticity of the skin
• Itching of the eyes
• Changes in skin pigmentation
• Enlarged groin
• Cataracts
• Light sensitivity
• Loss of vision

What Causes River Blindness?

A person may develop river blindness if infected female blackflies repeatedly bite them. Blackflies transmit the larvae of the worm Onchocercidae through their bite. During the course of six to 12 months, larvae migrate to the subcutaneous tissue of your skin and develop into adult worms. The cycle is repeated when a female blackfly bites a person infected with onchocerciasis and ingests the parasite [5].

An adult worm can live for ten to fifteen years and may produce millions of microfilariae. When microfilariae die, symptoms appear, so the longer you are infected, the more severe your symptoms may be. The most severe, longest-lasting cases result in blindness.

What Are The Risk Factors For River Blindness?

Since black flies breed in these areas, you are at a higher risk of contracting onchocerciasis if you live near fast-running streams or rivers in tropical areas. Residents, volunteers, and missionaries in areas of Africa are most at risk [6].

How Is River Blindness Diagnosed?

The doctor will perform a skin biopsy, known as a skin snip. A 2- to 5-milligram sample of skin will be removed during this procedure. The snips are taken from different body parts, usually six in total.

The Mazzotti test is an alternative test. The test is a skin patch test using diethylcarbamazine (DEC).

A less common form of testing is the nodulectomy, which involves surgically removing a nodule and then examining it for worms. There is also the option of performing an enzyme-linked immunosorbent assay (ELISA) test, which requires expensive equipment.

Two recent tests, the polymerase chain reaction (PCR) and the rapid-format antibody card test, appear promising [7].

How Is River Blindness Treated?

The World Health Organization recommends treating onchocerciasis with ivermectin at least once a year for 10 to 15 years. In addition, Mectizan Expert Committee (MEC)/APOC recommendations for the prevention and management of severe adverse events should be followed by affected countries [8].

On A Final Note...

The diagnosis of onchocerciasis remains a challenge for programs. However, WHO has verified that four countries are free of onchocerciasis after implementing successful elimination activities for decades: Colombia (2013), Ecuador (2014), Mexico (2015), and Guatemala (2016).