River blindness: causes, symptoms and treatment

River blindness, officially called ‘onchocerciasis’, is a parasitic infection spread by black flies. It causes skin irritation and itching, and it can lead to permanent blindness.

Infected black flies, which breed near fast-flowing rivers, can transmit river blindness. The parasitic infection can lead to vision loss.

What is river blindness?

River blindness, also called ‘onchocerciasis’, is a neglected tropical disease caused by a bite from an infected black fly. These flies breed near fast-flowing rivers.

Lady Jean Wilson, Sightsavers’ co-founder and the wife of Sir John Wilson, coined the term river blindness, which is now widely used. People also refer to the disease as ‘oncho’.

River blindness is the world’s second-most common infectious cause of blindness. As it can cause sight loss, people with the disease can experience stigma and discrimination about their disability.

What causes river blindness?

When a person is bitten by an infected black fly, worm larvae invade their body and grow into worms that can live for up to 15 years. Every day, female worms produce thousands of microscopic larvae, which spread throughout the body. If the larvae travel to the person’s eyes, it can cause permanent sight loss.

205 million people worldwide are at risk of river blindness

20.9 million people have the disease, mostly in sub-Saharan Africa

1.1 million people worldwide are blind due to river blindness

Source: WHO

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What are the symptoms of river blindness?

River blindness symptoms include:

Rashes and nodules beneath the skin
Inflammation and itching
Changes to skin colour and texture
Permanent vision loss

Short-term symptoms of river blindness include loss of vision, which can be reversed if the infection is treated early. If the microscopic larvae have been in the eyes for some time, the sight loss will be permanent but it won’t get worse if the person receives treatment.

When the microscopic larvae die in a person’s body, this can trigger a reaction that leads to immense discomfort. Larvae that die within the eyes can damage the cornea or inflame the optic nerve, leading to sight loss and blindness.

How is river blindness treated?

A photo of two hands. In one hand there are three tablets.

Medication

Medication can help to prevent the disease from spreading. It doesn’t cure blindness, but can help to stop any further sight loss.

Volunteers

Tablets donated by Sightsavers’ partners are distributed in communities by local volunteers who have received training.

A close-up showing black flies on a blade of grass

Fly monitoring

Health workers and researchers monitor the spread of infected black flies at sites near rivers, where they breed.

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How we’re fighting river blindness

Our aim is to eliminate river blindness in the countries where we work by 2025.

Most of our campaigns to protect people from river blindness take place in West Africa, where it’s most prevalent. We distribute medicine to treat and prevent the condition alongside another disease called lymphatic filariasis.

These two neglected tropical diseases often spread in the same areas and are treatable by giving large numbers of people medication. This is called mass drug administration.

In 2023, we helped to train more than 120,000 volunteers to administer medicine within their communities. With your support, we can reach even more people and protect them from river blindness so they don’t needlessly lose their sight.

Page last reviewed: April 2024
Next review due: April 2027
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