Causes Of Sleeping Sickness, And Geographical Distribution Of The Disease
Protozoa are single-celled organisms considered to be the simplest animal life form. The protozoa responsible for sleeping sickness are a flagellated variety (flagella are hair-like projections from the cell which aid in mobility) which exist only in Africa. The type of protozoa causing sleeping sickness in humans is referred to as the Trypanosoma brucei complex. It is divided further into Rhodesian (Central and East Africa) and Gambian (Central and West Africa) subspecies.
The Rhodesian variety live within antelopes in savanna and woodland areas, causing no disruption to the antelope's health. (While the protozoa cause no illness in antelopes they are lethal to cattle who may become infected.) The protozoa are acquired by tsetse flies who bite and suck the blood of an infected antelope or cow.
Within the tsetse fly, the protozoa cycle through several different life forms, ultimately migrating to the salivary glands of the tsetse fly. Once the protozoa are harbored in the salivary glands they can be deposited into the bloodstream of the fly's next blood meal.
Humans most likely to become infected by Rhodesian trypanosomes are game wardens or visitors to game parks in East Africa. The Rhodesian variety of sleeping sickness causes a much more severe illness with a greater likelihood of eventual death.
The Gambian variety of Trypanosoma thrives in tropical rain forests throughout Central and West Africa, does not infect game or cattle, and is primarily a threat to people dwelling in such areas. It rarely infects visitors.
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