Prevention of Blindness and Visual Impairment

Priority eye diseases


Onchocerciasis (river blindness)

Definition

Onchocerciasis is an insect-borne disease caused by a parasite Onchocerca volvulus and transmitted by blackflies of the species Simulium damnosum. Onchocerciasis is often called “river blindness” because the blackfly which transmits the disease abounds in fertile riverside areas, that frequently remain uninhabited for fear of infection. O. volvulus is almost exclusively a parasite of man. Adult worms live in nodules in a human body where the female worms produce high numbers of first-stage larvae known as microfilariae. They migrate from the nodules to the sub-epidermal layer of the skin where they can be ingested by blackflies. They further develop in the body of the insect from which more people can be infected. Eye lesions in humans are caused by microfilariae. They can be found in all internal tissues of the eye -- except the lens -- where they cause eye inflammation, bleeding, and other complications that ultimately lead to blindness.

Magnitude

Onchocerciasis is a major cause of blindness in many African countries. As a public health problem, the disease is most closely associated with West and Central Africa, but it is also prevalent in Yemen and six countries in Latin America. Onchocerciasis has in the past greatly reduced the economic productivity in infected areas and left vast tracts of arable land abandoned. It is estimated that there are about half a million blind people due to river blindness.

Prevention and treatment

Much progress has been made in fighting the disease in several countries through control of the blackfly, however, the disease can now also be treated with an annual dose of the drug ivermectine, Mectizan®, which also relieves the severe skin itching caused by the disease.

VISION 2020 role

Although river blindness was put on the priority disease list of VISION 2020, global initiatives had already been taken for onchocerciasis control. Beginning in 1974, effective vector control was implemented in West Africa through the Onchocerciasis Control Programme (OCP). Since 1996 mass community-based ivermectin treatment control programmes have been introduced by the African Programme for Onchocerciasis Control (APOC) in many other African countries and by the Onchocerciasis Elimination Programme in the Americas (OEPA) in the affected Latin American Countries. In 1992 an NGDO (Non-Governmental Development Organization) group, now called the Nongovernmental Development Organizations Coordination Group for Onchocerciacis Control, was formed to help promote worldwide interest and support for the use of ivermectin in endemic countries to eliminate onchocerciasis as a public health problem. Currently consisting of 9 international and 1 national partner NGDOs, the Group's activities are coordinated via its secretariat at WHO/HQ. Onchocerciasis control is not only an ongoing success story of disease control but also demonstrates the value of the synergy that comes from working together in partnership, and the economic return and social development that results from investments made in a disease control programme.

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Blindness and skin itching