River blindness

Around 35 million people are currently infected with river blindness, and roughly 300,000 of them are already irreversibly blind. Approximately 140 million people in Africa are at risk of infection.

What is river blindness?

River blindness (onchocerciasis) is caused by a worm that breeds in fast-flowing rivers. It is a major cause of blindness in west and central Africa. Sightsavers is combating it with the drug Mectizan®.

Symptoms of river blindness

As well as causing blindness and low vision, river blindness creates nodules on the skin and severe itching. This results in damage to the pigment and over time the skin becomes mottled. This causes further problems because the de-pigmented spots are more susceptible to skin cancer.

Impact of river blindness

River blindness is endemic in certain areas. This has two important social implications:

• children miss out on education because they are staying at home to act as full-time carers for older relatives who have become blind.
• people flee areas where the level of infection has hit hard, leaving 'ghost villages' behind. Unfortunately these infected areas are the ones with the most fertile land, closest to the river.

Causes of river blindness

River blindness is caused by a parasitical worm, onchocerca volvulus. The worm larvae are spread by the black simulium fly, which breeds in the high-oxygen water of fast-flowing rivers. The fly transmits the disease when it bites people, making those who live or work near the rivers vulnerable. Sightsavers is combating river blindness with the drug Mectizan®.

How river blindness spreads

When a black simulium fly becomes infected, the worm larvae spread to its saliva glands. When it bites a human, these pass into the skin. Here they develop into adults and form nodules under the skin. These adults then breed, producing thousands of larvae which spread throughout the whole body - including the eyes. This causes intense itching.

Impact on vision

A bite from an infected black simulium fly creates vulnerability to eye conditions such as glaucoma and cataract. But the biggest problem is when the worms die. The reaction of the person's immune system causes inflammation. If this happens in the eye it can cause blindness.

If infected at birth with river blindness it is common for people to have become blind by the time they have reached their 40s.

Controlling river blindness

River blindness is transmitted to humans by the black simulium fly which breeds in fast-flowing rivers. Sightsavers is combating it with the drug Mectizan®.

Ways to break the cycle of infection:

• reducing the number of flies by spraying affected areas with insecticide - an expensive and short-term solution.
• slowing fast-flowing rivers, making them unattractive as breeding grounds - expensive and not always practical.
• reducing exposure to flies by using protective garments - impractical because of the temperatures in affected countries.
• killing the adult worms by removing the worm 'nodules' - difficult because infected villages are often very remote and poor, making accessible surgery difficult.
• providing a yearly dose of the drug Mectizan® in affected areas.

Using Mectizan®

Mectizan® is an effective way to make the adult female worm temporarily infertile, killing larvae. If an uninfected simulium fly bites an infected person who has taken the drug, it will not itself become infected or infectious.

Problems with Mectizan®
Mectizan® is the best and most cost-effective way of tackling river blindness. But it is not without problems:

It needs to be administered regularly and across a whole community, not a simple task in remote areas with 140 million people at risk, training staff to distribute the drug is a major challenge for Sightsavers and our partners.