WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - African trypanosomiasis
Background of the disease
Human African trypanosomiasis, commonly known as sleeping sickness, which had been virtually eliminated from Africa during the 1960s, has come back as a disease of major public health importance. It is caused by two different species of trypanosomes (1), namely Trypanosoma brucei gambiense in West and Central Africa, and Trypanosoma brucei rhodesiense in East Africa. T. b. gambiense has a chronic and protracted course, and may last several years whereas T. b. rhodesiense is acute and can cause death in a matter of weeks or months. Both types of sleeping sickness are fatal if left untreated. Sleeping sickness is found uniquely in sub-Saharan Africa (Map 8.1).
Infection begins with the bite of an infected tsetse fly (Glossina species). During the first stage, trypanosomes multiply in the bloodstream and lymphatic system. This stage may last for years in the case of gambiense sleeping sickness. At this stage there are few specific symptoms apart from the characteristic swollen cervical lymph nodes. The second stage begins when the parasite crosses the blood-brain barrier and invades the central nervous system. It is only at this second stage that the disease presents neurological symptoms and characteristic signs, including alteration of the mental state, tone disorders, sensory disorders, and coordination problems. At this stage, sleeping sickness causes an alteration of the circadian sleep/wake cycle. Other consequences include endocrinological, cardiovascular and renal disorders. The natural progression of the disease without treatment is towards body wasting, somnolence, coma, and death.
Trypanosomes are able to evade the immune system of the host because of their enormous potential for antigenic variation (over 1000 variants). It is very difficult to treat, particularly after it has crossed the blood-brain barrier. The medicines themselves are often in short supply, difficult to administer, and can be fatal. It has been estimated that between 3 and 5% of those treated in the last stage of illness die from the treatment itself. In addition, resistance to currently used drugs is a serious problem (2). There is a clear need for new drugs, as well as better access to currently used ones.
Map 8.1 Distribution of gambiense and rhodesiense sleeping sickness in sub-Saharan Africa, 1999
(1)A trypanosome is a parasitic protozoa that causes a number of serious diseases in humans including sleeping sickness and Chagas disease.
(2) Barrett MP and Fairlamb AH The biochemical basis of arsenical-diamidine crossresistance in African trypanosomes, Parasitology Today, 1999, 15(4):136-140.