Human African trypanosomiasis, known as sleeping sickness, is a vector-borne parasitic disease. The parasites concerned are protozoa transmitted to humans by tsetse flies found in vegetation by rivers and lakes, gallery-forests and vast stretches of wooded savannah in Africa.
Sleeping sickness occurs only in sub-Saharan Africa in regions where tsetse flies are endemic. For reasons not yet known, 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. Another human form of trypanosomiasis occurs in the Americas and is known as Chagas disease. Sleeping sickness affects those remote and rural areas where health systems are weak or non-existent. The disease is found where socio-economic problems such as political instability, displacement of populations, war and poverty exist. Within a given focus, the intensity of the disease can vary considerably from one village to the next and can spread to cover a whole region.
Human African trypanosomiasis takes two forms, depending on the parasite involved:
• Trypanosoma brucei gambiense is found in central and West Africa. It causes chronic infection; 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 is found in southern and East Africa. It causes acute infection that emerges after a few weeks. It is more virulent and develops more rapidly, making it easier to detect clinically.
Geographical distribution of the disease
Sleeping sickness threatens over 60 million people in 36 countries of sub-Saharan Africa. Only 3 to 4 million of these people are under surveillance with regular examination or access to a health centre that can provide screening. Detection of the disease calls for major human and material resources such as well-equipped health centres and qualified staff. Because such resources are lacking, most people with sleeping sickness die before they can ever be diagnosed.
In certain areas of Angola, the Democratic Republic of Congo and southern Sudan, prevalence is between 20% and 50%. Sleeping sickness has become the first or second greatest cause of mortality, ahead of HIV/AIDS, in these provinces. Countries are categorized according to prevalence.
• Countries where there is an epidemic of the disease, in terms of very high cumulated prevalence and high transmission: Angola, Democratic Republic of Congo and Sudan;
• Highly endemic countries, where prevalence is moderate but increase is certain: Cameroon, Central African Republic, Chad, Congo, Côte d’Ivoire, Guinea, Mozambique, Uganda and United Republic of Tanzania;
• Countries where the endemic level is low: Benin, Burkina Faso, Equatorial Guinea, Gabon, Kenya, Mali, Togo and Zambia; and
• Countries whose present status is not clear: Botswana, Burundi, Ethiopia, Liberia, Namibia, Nigeria, Rwanda, Senegal and Sierra Leone.
If the disease is diagnosed early, the chances of cure are high. The type of treatment depends on the phase of the disease: initial or neurological. Success in the latter phase depends on having a drug that can cross the blood-brain barrier to reach the parasite. Four drugs have been used until now.
First phase treatments
Suramine is used in treatment of the initial phase of T. b. rhodesiense. There are certain undesirable effects, especially on the digestive tract.
Pentamidine is used in treatment of the initial phase of T. b. gambiense sleeping sickness. In spite of a few undesirable effects, it is well tolerated by patients. Future production is guaranteed by an agreement between WHO and the company Aventis.
Second phase treatments
Melarsoprol is at present the only drug available on the market to treat the advanced stage of sleeping sickness, no matter which parasite is the cause. It is the last arsenical derivative in existence. The undesired effects are drastic: they include reactive encephalopathy (an often fatal hyperacute neurological complication of an allergic nature) in 3 to 10% of cases; those who survive the encephaloathy suffer serious neurological sequelae. Furthermore, there is considerable resistance to the drug, rising to 30% in parts of central Africa.
Eflornithine was registered in 1990 as an alternative to melarsoprol treatment. It is effective only against T. b. gambiense. The regimen is strict and hard to apply. Production ceased in 1999. Last year, the manufacturer transferred the product licence to WHO, which has undertaken several initiatives to seek a new source of production. In short, most drugs are old, difficult to administer in poor conditions and by no means always successful. Early diagnosis of the disease, which would guarantee low-risk treatment on an outpatient basis, can rarely be achieved. It is essential that a new manufacturer is found to continue production and marketing of eflornithine, the only currently available medicine which can treat the neurological phase of T. b. gambiense.
Faced with the resurgence of sleeping sickness, WHO is coordinating activities in endemic countries and mobilizing a wide range of partners for this purpose. The Programme for Surveillance and Control of African Trypanosomiasis (PSCAT) includes national control programmes, nongovernmental organizations (NGOs), donor countries, private foundations, regional institutions, research centres and universities.
The objectives of PSCAT are:
• Coordination of the sleeping sickness control network to ensure that field activities are sustainable;
• Strengthening of existing surveillance systems;
• Development of the network for study of treatment and drug resistance;
• Promotion of inter-agency collaboration, for example with the FAO; and
• Development of an information system and training activities.