Sleeping sickness is an endemic disease confined to equatorial Africa and characterized in its terminal stages by sleepiness, torpor, and coma. Sleeping sickness has been known since 1800. It was then endemic in a few localities, but in recent years it has become widespread. The disease is caused by a blood parasite, the Trypanosoma gambiense, which is conveyed by two varieties of the tsetse fly, Glossina palpalis and Glossina morsitans. Wild and domestic animals act as reservoirs for the sickness, the disease in the animal being known as nagana, the tsetse fly disease of cattle.
Two types of sleeping sickness are recognized. The Uganda type, carried by Glossina palpalis and confined to the watercourses and lake shores, was first identified in 1901. It is violently epidemic. The variety occurring in Nyassaland and Rhodesia has been known only since 1908, is highly fatal but not epidemic. The fly that is the conveyer in this case is Glossina morsitans, which is independent of water.
The name "sleeping sickness" is also applied popularly to an unrelated group of diseases which cause coma and are known medically as encephalitis.
