What causes sleeping sickness?
Sleeping sickness is caused by two organisms, T. brucei rhodesiense and T. brucei gambiense. The more severe form of the illness is caused by rhodesiense. After a person is bitten by an infected fly, a red painful swelling develops at the site of the fly bite, similar to that seen in Chagas disease. From this site, the parasite invades the blood stream, causing episodes of fever, headache, sweating, and generalized enlargement of the lymph nodes. Parasites then invade the
central nervous system (early with rhodesiense and later with gambiense) where they produce the symptoms typical of sleeping sickness. Ultimately the parasites invade the brain, first causing behavioral changes such as fear and mood swings, followed by headache, fever, and weakness. Simultaneously, the patient may develop myocarditis.
Protozoa are single-celled organisms considered to be the simplest life form in the animal kingdom. The protozoa responsible for sleeping sickness are a variety which bear numerous flagella (hair-like projections from the cell which help the cell to move). These protozoa exist only on the continent of Africa. The type of protozoa causing sleeping sickness in humans is referred to as the Trypanasoma brucei complex, which can be divided further into Rhodesian (Central and East African) and Gambian (Central and West African) subspecies. The Rhodesian variety live within antelopes in savanna and woodland areas, and they cause no problems with the antelope's health. The protozoa are then acquired by tsetse flies when they bite and suck the blood of an infected antelope or cow. Within the tsetse fly, the protozoa cycle through several different life forms; ultimately they migrate to the salivary glands of the tsetse fly. Once the protozoa are harbored in the salivary glands, they are ready to be deposited into the bloodstream of the fly's next source of a blood meal.
Without treatment, death may occur within six months from cardiac failure, or from rhodesiense infection itself. Gambiense infection may require up to two years before symptoms of infection in the central nervous system appear.
Gambiense-infected people develop drowsiness during the day, but insomnia at night. Sleep becomes uncontrollable as the disease progresses until the patient becomes comatose. Risk factors include living in those parts of Africa where the disease is found and being bitten by tsetse flies. The incidence is extremely low in the U.S. -- it is only found in travelers who have visited or lived in those areas.