Definition of the disease

Human African trypanosomiasis, known as sleeping sickness, is a vector-borne parasitic disease. Trypanosoma, the parasites concerned, are protozoa transmitted to humans by tsetse flies (glossina). Tsetse flies live in Africa, and they are found in vegetation by rivers and lakes, gallery-forests and vast stretches of wooded savannah.

Another human form of trypanosomiasis (Human American Trypanosomiasis) occurs in the Americas and is known as Chagas disease.

· Sleeping sickness occurs only in sub-Saharan Africa, in regions where tsetse flies are endemic. For reasons as yet unknown, there are many regions where tsetse flies are found, but sleeping sickness is not.

· The rural populations that live in such environments and depend on them for agriculture, fishing, animal husbandry or hunting are the most exposed - along with their livestock - to the bite of the tsetse fly.

· Sleeping sickness affects remote and rural areas where health systems are least effective, or non-existent. It spreads with socio-economic problems such as political instability, displacement of populations, war and poverty.

· It develops in foci whose size can range from a village to an entire region. Within a given focus, the intensity of the disease can vary considerably from one village to the next.

Human African trypanosomiasis takes two forms, depending on the parasite involved:

· Trypanosoma brucei gambiense (T.b. gambiense) is found in central and West Africa. It causes chronic infection, which does not mean benign. A person can be infected for months or even years without obvious symptoms of the disease emerging. When symptoms do emerge, the disease is already at an advanced stage.

· Trypanosoma brucei rhodesiense (T.b. rhodesiense) is found in southern and east Africa. It causes acute infection that emerges after a few weeks. It is more virulent than the other strain and develops more rapidly, which means that it is more quickly detected clinically.