What is onchocerciasis?
The world's second leading infectious cause of blindness, onchocerciasis is often called "river blindness" because in extreme cases, it can cause blindness, and because the blackfly, which carries it, abounds in fertile riverside areas. More than 120 million people in 37 countries in Africa, Latin America, and Yemen are at risk of the disease. Frequently fertile river farmland remains uninhabited for fear of infection. Experts estimate that 18 million people are infected with river blindness, 6.5 million suffer from severe itching or dermatitis, 770,000 people suffer serious sight impairment, and 270,000 are blind.
Where are the high risk destinations for infection?
Onchocerciasis is present in 36 countries, 29 of them in sub-Saharan Africa, Yemen in the Arabian peninsula and six in the Americas. As a public health problem the disease is most closely associated with Africa, where it constitutes a serious obstacle to socio-economic development.
Out of some 120 million people world-wide who are at risk of onchocerciasis, 96% are in Africa. A total of 18 million people are infected with the disease and have tiny worms under the skin (dermal microfilariae), of whom 99% are in Africa. The worst affected countries are Angola, Burundi, Cameroon, Chad, the Central African Republic (CAR), the Congo, the Democratic Republic of the Congo, Ethiopia, Equatorial-Guinea, Gabon, Kenya, Liberia, Malawi, Mozambique, Nigeria, Rwanda, Uganda, Sudan and Tanzania.
How is onchocerciasis transmitted?
Onchocerciasis is caused by Onchocerca volvulus, a parasitic worm that lives for up to 14 years in the human body. It is spread through the bite of a blackfly of the Simulium damnosum species complex, which breeds in fast-flowing rivers and streams.
When the fly bites, it deposits the larvae of a parasitic worm, which matures to adulthood and produces millions of tiny worms, called microfilaria. Adults emerge after 8-12 days and live for up to four weeks, during which they can cover hundreds of kilometres in flight.
Each adult female worm, thin but more than .5 metre in length, produces millions of microfilariae (microscopic larvae) that migrate throughout the body.
After mating, the female blackfly seeks a bloodmeal and may ingest microfilariae if the meal is taken from a person infected with onchocerciasis.
A few of these microfilariae may transform into infective larvae within the blackfly, which are then injected into the person from whom the next meal is taken and subsequently develop into adult parasites, thus completing the life cycle of the parasite.
What are the symptoms of onchocerciasis?
When the microfilariae migrate throughout the body and give rise to a variety of symptoms rashes, lesions, intense itching and depigmentation of the skin; lymphadenitis, which results in hanging groins and elephantiasis of the genitals, general debilitation and serious visual impairment, including blindness.
How soon do onchocerciasis symptoms occur?
Onchocerciasis manifestations begin to occur in persons one to three years after the injection of infective larvae.
How is onchocerciasis treated?
The development of ivermectin in the 1980's provided for the first time a safe, effective drug capable of reducing the numbers of skin microfilariae in infected people and resulting in clinical improvement and decreased transmission of infection.
What can I do?
Take precautions to avoid blackfly bites and seek medical advice if you feel you have been bitten.
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