Tropical Diseases

River Blindness

A close up of an old man's eyes.

Onchocerciasis is an infection caused by the parasitic worm spread by the bite of an infected blackfly, mostly found in rural agricultural areas in sub-Saharan Africa. The disease is called River Blindness because the fly that transmits infection breeds in rapidly flowing streams and the infection can cause blindness.

How dangerous is Onchocerciasis? 

Worldwide onchocerciasis is second only to trachoma as an infectious cause of blindness and can cause debilitating and disfiguring skin disease.


Who is at risk?

The people most at risk for acquiring onchocerciasis are those who live near rivers where there are Simulium blackflies which are mostly found in rural agricultural areas in sub-Saharan Africa. Usually, many bites are needed before being infected. 


People who travel for periods of less than three months to areas where the parasite is found have a low chance of becoming infected with O. volvulus.


How many people are affected by Onchocerciasis?

The World Health Organization's (WHO) expert committee on onchocerciasis estimates that at least 25 million people are infected, and 123 million people live in areas that put them at risk of infection. About 300,000 people are blind because of the parasite and another 800,000 have visual impairment.

A man in a suit and tie sits at a table.
Our vision is to improve the quality of life and the health of people suffering from neglected diseases.
Dr. Bernard Pécoul
Executive Director of Drugs for Neglected Diseases Initiative (DNDi), Switzerland

Where is Onchocerciasis found? 

Onchocercal infections mainly occur in tropical areas. More than 99% of infected people live in 31 countries in sub-Saharan Africa: Angola, Benin, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, Republic of Congo, Côte d’Ivoire, Democratic Republic of the Congo, Equatorial Guinea, Ethiopia, Gabon, Ghana, Guinea, Guinea-Bissau, Kenya, Liberia, Malawi, Mali, Mozambique, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, South Sudan, Sudan, Togo, Uganda, United Republic of Tanzania. The disease is also transmitted in Yemen in the Middle East, in one focal area in Venezuela and one in Brazil.


How do people get Onchocerciasis?

Onchocerciasis is transmitted to humans through exposure to repeated bites of infected blackflies of the genus Simulium.

Watch the following video to hear Professor Assani's story and the impact of the disease on him, as well as his call for more innovation and research.

Bayer contribution

Bayer has signed in 2014 a collaboration agreement with the Drugs for Neglected Diseases initiative (DNDi) - to develop together a new treatment option for river blindness. DNDi is a collaborative, patients’ needs-driven, non-profit drug research and development (R&D) organization that is developing new treatments for neglected diseases. The currently available drugs against river blindness are only effective against the parasites' microfilariae, i.e. larvae and young worms. However, the adult worms survive until the end of their natural lifespan and produce more and more new generations of offspring. Thus the drugs have to be given as MDA for up to 15 years. The compound in focus of the cooperation, is a macrofilaricide which also kills the adult nematodes. This could significantly shorten the duration of treatment, which would mean significant progress in the long-term fight against river blindness