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African trypanosomiasis (sleeping sickness)
DEFINITION OF THE DISEASE
Human African Trypanosomiasis, also known as sleeping sickness, is a vector-borne parasitic disease. The parasites concerned are protozoa belonging to the Trypanosoma Genus. They are transmitted to humans by tsetse fly (Glossina Genus) bites which have acquired their infection from human beings or from animals harbouring the human pathogenic parasites.
Tsetse flies are found in Sub-Saharan Africa. Only certain species transmit the disease. Different species have different habitats. They are mainly found in vegetation by rivers and lakes, in gallery-forests and in vast stretches of wooded savannah.
Human African Trypanosomiasis takes two forms, depending on the parasite involved:
Another form of trypanosomiasis occurs in 15 Central and South American countries. It is known as American Trypanosomiasis or Chagas disease. The causal organism is a different species from those causing the African form of the disease.
Other parasite species and sub-species of the Trypanosoma Genus are pathogenic to animals and cause animal Trypanosomiasis in many wild and domestic animal species (in cattle the disease is called Nagana, a Zulu word meaning “to be depressed”). Animals can host the human pathogen parasites, especially T.b. rhodesiense; thus domestic and wild animals are an important parasite reservoir. Animals can also be infected with T.b. gambiense, however the precise epidemiological role of this reservoir is not yet well known. This disease kills animals.
The disease in domestic animals and particularly cattle is a major obstacle to the economic development of the rural areas affected.
MAJOR HUMAN EPIDEMICS
There have been several epidemics in Africa over the last century: one between 1896 and 1906, mostly in Uganda and the Congo Basin, one in 1920 in a number of African countries and the most recent one beginning in 1970. The 1920 epidemic was controlled thanks to mobile teams who organized the screening of millions of people at risk. By the mid 1960s, the disease had almost disappeared. After that success, surveillance was relaxed, and the disease reappeared in several areas over the last thirty years. Recent WHO efforts and those of national control programmes and nongovernmental organizations (NGOs) have stopped and begun to reverse the upward trend of new cases.
GEOGRAPHICAL DISTRIBUTION OF THE DISEASE
Sleeping sickness threatens millions of people in 36 countries of sub-Saharan Africa. However, only a small fraction of them are under surveillance with regular examination, have access to a health centre that can provide diagnostic facilities, or are protected by vector control interventions.
Progress in disease control
Current situation in endemic countries
The prevalence of the disease differs from one country to another as well as in different parts of a single country. In 2005, major outbreaks have been observed in Angola, the Democratic Republic of Congo and Sudan. In Central African Republic, Chad, Congo, Cote d’Ivoire, Guinea, Malawi, Uganda and United Republic of Tanzania sleeping sickness remains an important public health problem. Countries such as Burkina Faso, Cameroon, Equatorial Guinea, Gabon, Kenya, Mozambique, Nigeria, Rwanda, Zambia and Zimbabwe are reporting fewer than 50 new cases per year. In countries such as Benin, Botswana, Burundi, Ethiopia, Gambia, Ghana, Guinea Bissau, Liberia, Mali, Namibia, Niger, Senegal, Sierra Leone, Swaziland and Togo transmission seems to have stopped and no new cases have been reported for several decades. Nonetheless, it is difficult to assess the current situation in a number of endemic countries because of a lack of surveillance and diagnostic expertise.
INFECTION AND SYMPTOMS
The disease is transmitted through the bite of an infected tsetse fly. At first the trypanosomes multiply in subcutaneous tissues, blood and lymph. In time, the parasites cross the blood-brain barrier to infect the central nervous system. The process can take years with T.b. gambiense.
The first stage of the disease, known as a haemolymphatic phase, entails bouts of fever, headaches, joint pains and itching. The second stage, known as the neurological phase, begins when the parasite crosses the blood-brain barrier and invades the central nervous system. In general this is when the signs and symptoms of the disease appear: confusion, sensory disturbances and poor coordination. Disturbance of the sleep cycle, which gives the disease its name, is an important feature of the second stage of the disease. Without treatment, sleeping sickness is fatal.
Disease management is performed in three steps:
Diagnosis must be made as early as possible and before the neurological stage in order to avoid complicated, difficult and risky treatment procedures.
The long, asymptomatic first stage of T.b. gambiense sleeping sickness is one of the factors that requires the use of exhaustive active screening of the population at risk in order to identify patients at an early stage and reduce transmission. Exhaustive screening of exposed populations requires a major investment in human and material resources. In Africa such resources are often scarce, particularly in remote areas where the disease is mostly found. As a result, many infected individuals may die before they can ever be diagnosed and treated.
The type of treatment depends on the stage of the disease. The drugs used in the first stage of the disease are less toxic, easier to administer and more effective. The earlier the identification of the disease, the better the prospect of a cure. Treatment success in the second stage depends on a drug that can cross the blood-brain barrier to reach the parasite. Such drugs are quite toxic and complicated to administer. Four drugs are registered for the treatment of sleeping sickness and provided free of charge to endemic countries through a WHO private partnership with sanofi-aventis (pentamidine, melarsoprol and eflornithine) and Bayer AG (suramin).
First stage treatments
Second stage treatments
THE ROLE OF THE WORLD HEALTH ORGANIZATION
The resurgence of sleeping sickness since the 1970s led WHO to reinforce its Human African Trypanosomiasis programme. The objective is to coordinate activities in endemic countries and mobilize a wide range of partners.
The WHO Programme provides support and technical assistance to national control programmes. A network has been established including donor countries, private foundations, NGOs, regional institutions, research centres and universities to participate in surveillance and control, and to undertake research projects for the development of new drugs and diagnostic tools.
The objectives of the WHO Programme are to:
Sources: US Department of Health; The World Health Organization