Onchocerciasis (River Blindness)

Distribution:
Mainly western equatorial Africa, South and Central America and the Yemen.

The vector:
The blackfly (Simulium) which breeds in swiftly flowing rivers. Infective larvae enter the body and develop into male or female adults. If fertilization occurs the female releases microfilariae which are taken up once again by the blackfly.

The illness:
This is due to micro-filariae in the skin which cause itch and inflammation. Scratching causes excoriation and secondary infection. Most changes occur on the lower half of the body. More seriously, microfilariae readily invade the cornea , and on rare occasions the retina, causing damage - hence the name 'river blindness'.

Treatment:
Ivermectin renders the female worms temporarily infertile. It does not kill them and so treatment has to be repeated for several years.

Prevention is through avoiding black fly bites.

Recommended for more information:
'Lecture Notes in Tropical medicine' . Dion R. Bell. Blackwell Publications ISBN 0-632-02445-0 or ' Mansons textbook of Tropical Diseases' Ed.G.C.Cook WB Sanuders Company Ltd ISBN 0-7020-1764-7.