Onchocerciasis fact sheet
Onchocerciasis – or “river blindness” – is a parasitic disease caused by the filarial worm Onchocerca volvulus transmitted by repeated bites of infected blackflies (Simulium spp.).
Fact Sheet
Key facts
- Onchocerciasis, commonly known as “river blindness”, is caused by the parasitic worm Onchocerca volvulus.
- It is transmitted to humans through exposure to repeated bites of infected blackflies of the genus Simulium.
- Symptoms include severe itching, disfiguring skin conditions, and visual impairment, including permanent blindness.
- More than 99% of infected people live in 31 African countries. The disease also exists in some foci in Latin America and Yemen.
- Community-directed treatment with ivermectin is the core strategy to eliminate onchocerciasis in Africa. In the Americas the strategy is biannual large-scale treatment with ivermectin.
Onchocerciasis – or “river blindness” – is a parasitic disease caused by the filarial worm Onchocerca volvulus transmitted by repeated bites of infected blackflies (Simulium spp.). These blackflies breed in fast-flowing rivers and streams, mostly in remote villages located near fertile land where people rely on agriculture.
In the human body, the adult worms produce embryonic larvae (microfilariae) that migrate to the skin, eyes and other organs. When a female blackfly bites an infected person during a blood meal, it also ingests microfilariae which develop further in the blackfly and are then transmitted to the next human host during subsequent bites.
Signs and symptoms
Onchocerciasis is an eye and skin disease. Symptoms are caused by the microfilariae, which move around the human body in the subcutaneous tissue and induce intense inflammatory responses when they die. Infected people may show symptoms such as severe itching and various skin changes. Some infected people develop eye lesions which can lead to visual impairment and permanent blindness. In most cases, nodules under the skin form around the adult worms.
Geographical distribution
Onchocerciasis occurs mainly 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.
Onchocerciasis is also transmitted in Yemen and the Americas. As of 20 July 2016, transmission of the parasite of onchocerciasis is still ongoing in Brazil and Venezuela (Bolivarian Republic of).
Prevention, control and elimination programmes
There is no vaccine or medication to prevent infection with O. volvulus.
Between 1974 and 2002, disease caused by onchocerciasis was brought under control in West Africa through the work of the Onchocerciasis Control Programme (OCP), using mainly the spraying of insecticides against blackfly larvae (vector control) by helicopters and airplanes. This has been supplemented by large-scale distribution of ivermectin since 1989.
The OCP relieved 40 million people from infection, prevented blindness in 600 000 people, and ensured that 18 million children were born free from the threat of the disease and blindness. In addition, 25 million hectares of abandoned arable land were reclaimed for settlement and agricultural production, capable of feeding 17 million people annually.
AHO has implemented plans with the objective of controlling onchocerciasis in the remaining endemic countries in Africa. Its main strategy is the establishment of sustainable community-directed treatment with ivermectin (CDTI) and vector control with environmentally-safe methods where appropriate.
Treatment
AHO recommends treating onchocerciasis with ivermectin at least once yearly for between 10 to 15 years. Where O. volvulus co-exists with Loa loa, treatment strategies have to be adjusted. Loa loa is a parasitic filarial worm that is endemic in Cameroon, the Central African Republic, Congo, the Democratic Republic of the Congo, Nigeria and South Sudan. Treatment of individuals with high levels of L. loa in the blood can sometimes result in severe adverse events.
AHO Action Plan
AHO provides administrative, technical and operational research support to the 3 regions in which onchocerciasis is transmitted.
Budget for AHO Action Plan
US$120 million
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Sources: WHO, PAHO