African sleeping sickness is caused by infection with a unicellular parasite. There are two subspecies of these parasites: the West African or Trypanosoma brucei gambiense and the East African or T. brucei rhodesiense. They cannot be differentiated from each other on morphological grounds. There are subspecies, which is a bit confusing. Trypanosoma brucei gambiense type 1 is genetically distinct from T. b. brucei en T. b. rhodesiense. T. b. gambiense type 2 resembles T. b. brucei.

Transmission takes place through the bite of an infected tsetse fly (Glossina). [Since they are transmitted via tsetse saliva, they are also known as "salivaria", as opposed to Trypanosoma cruzi, which belongs to the "stercoraria" because it is transmitted via the faeces of a bug]. In exceptional cases mechanical transmission takes place via other biting flies (tabanids). Congenital infections are rare. Sexual transmission seems to be extremely rare.

African trypanosomiasis or sleeping sickness occurs exclusively in Africa. The area of distribution lies between 14° north of the Equator and 29° south of the Equator. It occurs locally in 36 countries, with a collective population at risk of about 50 million people. There are some 200 areas where the infection is concentrated. The areas of distribution of West African and East African trypanosomiasis show little overlap (e.g. in Uganda). The disease is characterised by fever, lymph node swelling, general malaise and inflammation of the central nervous system. If left untreated, the disease has a fatality rate of practically 100%. There is possibly an increasing resistance to the medications used at present, which is very curious if one consideres the number of cases treated. It was estimated in 1997 that in Africa there were about 300,000 new cases per year. Some estimates for 2003 put the total number at 500,000, but this is probably an overestimate.

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