Onchocerciasis

 

Onchocerciasis

PKGhatak, MD.

Onchocerciasis is known as River Blindness. 31 nations in Africa, Yemen and several countries in South and Central America where Onchocerciasis is endemic.

A black fly of Simulium group, is the vector, the worm is Onchocerca volvulus and humans are victims and harbor this Nematode worm. In 1915, Dr. Rodolfo Robles found the worm and linked it to eye diseases.

The life cycle of Onchocerca is almost identical to that of Loia loia worm. The areas of exceptions are the vector is black fly, the habitat of black fly is the fast running rivers and the nematode is Onchocerca volvulus.

The important difference in the pathogenicity of human illness is that the microfilaria are allergenic to humans, while the adult worms are not. The microfilaria wonders around the body underneath the skin in the subcutaneous tissue and produces several different types of skin lesions. The eye diseases produced by Onchocerca are conjunctivitis, corneal scar, uveitis, glaucoma, macular edema and optic atrophy and blindness. Chronic sclerosing keratitis is the main cause of blindness. Onchocerca is the second most common cause of mass blindness. 17 million people are at risk and 800, 000 have already lost their eyesight.

Onchocerca microfilaria is in symbiotic relation with the bacteria Walachia group. The dying microfilaria releases bacterial antigen that produces sensitization and allergic reaction, and when Ivermectin produces mass killing of microfilaria the overabundance of antigen produces anaphylactic shock and deaths.

WHO has elimination programs for this illness. WHO distributes Ivermectin tablets to the participating nations. And has already eliminated it from several countries in South America, Columbia being the first. Ivermectin kills the microfilaria but not the adult worm, as a result, Ivermectin had to be repeated every 6 to 12 months intervals.

Serological tests and PCR tests are available for diagnosis but visualization of microfilaria in the blood is the mainstay locally.

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