Onchocerciasis

African Programme for Onchocerciasis Control (APOC)

Neglected Tropical Diseases

Factsheet

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.
• In July 2016, Guatemala became the fourth country in the world after Colombia (2013), Ecuador (2014), and Mexico (2015) to be verified free of onchocerciasis after successfully implementing elimination activities for decades.

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.

Onchocerciasis, or river blindness, is a parasitic eye and skin disease. It is caused by a worm (filaria) and is transmitted to humans through a type of biting blackfly. These flies breed in fast-flowing streams and rivers within intertropical zones, increasing the risk of blindness to individuals living nearby.

Once in the body, female adult worms release up to 1000 eggs per day. These move through the body, and when they die they become very toxic to the skin and eyes. The symptoms of onchocerciasis include skin rashes, lesions, intense itching and skin depigmentation. River blindness is the world's second leading infectious cause of blindness.

The worms can be found in all internal tissues of the eye – except the lens – where they cause eye inflammation, bleeding and other complications. After repeated years of exposure, these lesions may lead to irreversible blindness and disfigurative skin diseases that are often called "leopard" skin or "lizard" skin.

About 90% of the disease occurs in the African Region. In some communities, about 50% of men over the age of 40 have been blinded by the disease. People often flee the fertile river valleys to settle in safer, less productive upland country.