Onchocerciasis, commonly known as river blindness, is caused by the filaria Onchocerca volvulus. The name "river blindness" is derived from the occurrence of the disease in focal areas along rivers and streams where the blackfly (Similium) breeds in fast-flowing water. The blackfly can travel several kilometres and does not respect international borders.
The disease is characterised by a few adult worms encased in nodules and the invasion of the body by microfilaria produced by the adult worms. It is endemic in equatorial Africa - West and Central - and Central and South America. It is estimated that there are about half a million blind people because of onchocerciasis.
The adult worm has a lifespan of 15-30 years. The microfilaria is sucked up by the blackfly when it takes its blood meal. Subsequently, division within the blackfly gives rise to latter stages of the larva, which are re-injected into the skin of the next victim of the blackfly's bite. The microfilariae migrate under and through the skin and may mature in about one year. Newly produced microfilariae migrate to the eye through the skin or blood.
Clinical manifestations of onchocerciasis can be divided into extraocular and ocular manifestations.
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