Trypanosomiasis (Human)

Primary reference(s)

WHO, 2020. Trypanosomiasis, human African (sleeping sickness). World Health Organization (WHO). Accessed 26 October 2020.

Additional scientific description

Human African trypanosomiasis, also known as sleeping sickness, is a vector-borne parasitic disease. It is caused by infection with protozoan parasites belonging to the genus Trypanosoma. They are transmitted to humans by tsetse fly (Glossina genus) bites which have acquired their infection from humans or from animals harbouring human pathogenic parasites (WHO, 2020).

Tsetse flies are only found in sub-Saharan Africa and only certain species transmit the disease. For reasons so far unexplained, in many regions where tsetse flies are found, sleeping sickness is not. Rural populations in regions where transmission occurs and which depend on agriculture, fishing, animal husbandry or hunting are the most exposed to the tsetse fly and thus to the disease. The disease develops in areas ranging from a single village to an entire region. Within an infected area, the intensity of the disease can vary from one village to the next (WHO, 2020).

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

• T. brucei gambiense is found in 24 countries in west and central Africa. This form currently accounts for 98% of reported cases of sleeping sickness and causes a chronic infection (WHO, 2020).
• T. brucei rhodesiense is found in 13 countries in eastern and southern Africa. The disease develops rapidly and invades the central nervous system. Only Uganda presents both forms of the disease, but in separate zones (WHO, 2020).

Another form of trypanosomiasis occurs mainly in Latin America. It is known as American trypanosomiasis or Chagas disease. The causal organism belongs to a different Trypanosoma subgenus and is transmitted by a different vector (WHO, 2020).

Major human epidemics have occurred in Africa over the past 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 epidemic started in 1970 and lasted until the late 1990s (WHO, 2020).

The 1920 epidemic was controlled by mobile teams which carried out the screening of millions of people at risk. By the mid-1960s, the disease was under control with less than 5000 cases reported in the whole continent. After this success, surveillance was relaxed, and the disease reappeared, reaching epidemic proportions in several regions by 1970. The efforts of the World Health Organization (WHO), national control programmes, bilateral cooperation and non-governmental organisations (NGOs) during the 1990s and early 21st century reversed the curve (WHO, 2020).

Since the number of new human African trypanosomiasis cases reported between 2000 and 2018 dropped by 95%. The WHO neglected tropical diseases road map targeted its elimination as a public health problem by 2020 and interruption of transmission (zero cases) for 2030. Sleeping sickness threatens millions of people in 36 countries in sub-Saharan Africa. Many of the affected populations live in remote rural areas with limited access to adequate health services, which complicates the surveillance and therefore the diagnosis and treatment of cases. In addition, displacement of populations, war and poverty are important factors that facilitate transmission (WHO, 2020).

Currently, the disease incidence differs from one country to another as well as in different parts of a single country. In the past 10 years, over 70% of reported cases occurred in the Democratic Republic of the Congo (WHO, 2020).

Angola, Central African Republic, Chad, Congo, Gabon, Guinea, Malawi and South Sudan declared between 10 and 100 new cases in 2018. Cameroon, Côte d’Ivoire, Equatorial Guinea, Kenya, Uganda, United Republic of Tanzania, Zambia and Zimbabwe declared between 1 and 10 new cases in 2018. Countries such as Burkina Faso, Ghana, and Nigeria, have reported sporadic cases in the past 10 years. Countries like Benin, Botswana, Burundi, Ethiopia, Gambia, Guinea Bissau, Liberia, Mali, Mozambique, Namibia, Niger, Rwanda, Senegal, Sierra Leone, Swaziland and Togo have not reported any new cases for over a decade. Transmission of the disease seems to have stopped in some of these countries but there are still some areas where it is difficult to assess the exact situation because the unstable social circumstances and/or difficult accessibility hinder surveillance and diagnostic activities (WHO, 2020).

The disease is mostly transmitted through the bite of an infected tsetse fly but there are other ways in which people are infected. These include: mother-to-child infection (the trypanosome can cross the placenta and infect the foetus); mechanical transmission through other blood-sucking insects, however, it is difficult to assess its epidemiological impact; accidental infections in laboratories due to pricks with contaminated needles; and transmission of the parasite through sexual contact (WHO, 2020).

Symptoms of the disease in the first stage start when the trypanosomes multiply in subcutaneous tissues, blood and lymph. This is also called the haemo-lymphatic stage, which entails bouts of fever, headaches, enlarged lymph nodes, joint pains and itching. In the second stage the parasites cross the blood-brain barrier to infect the central nervous system. This is known as the neurological or meningo-encephalic stage. In general, this is when more obvious signs and symptoms of the disease appear: changes of behaviour, confusion, sensory disturbances and poor coordination. Disturbance of the sleep cycle, which gives the disease its name, is an important feature. Without treatment, sleeping sickness is considered fatal although cases of healthy carriers have been reported (WHO, 2020).

Metrics and numeric limits

In 1998, almost 40,000 cases of trypanosomiasis were reported, but estimates were that 300,000 cases were undiagnosed and therefore untreated. During the last epidemic the prevalence reached 50% in several villages in Angola, the Democratic Republic of the Congo, and South Sudan. Sleeping sickness was the first or second greatest cause of mortality in those communities, even ahead of HIV/AIDS. In 2009, after continued control efforts, the number of cases reported dropped below 10,000 (9878) for the first time in 50 years. This decline in number of cases has continued with 997 new cases reported in 2018, the lowest level since the start of systematic global data-collection 80 years ago. The estimated population at risk is 65 million people (WHO, 2020).

Examples of drivers, outcomes and risk management

The WHO and its partners provide support and technical assistance to national control programmes and provide the antitrypanosome medicines free of charge to endemic countries through public-private partnerships with Sanofi (pentamidine, melarsoprol, eflornithine, fexinidazole) and Bayer HealthCare (suramin, nifurtimox) (WHO, 2021).

In 2008, the WHO launched the Atlas of human African Trypanosomiasis initiative to map at village level all reported cases (WHO, 2015). This initiative is jointly implemented with the Food and Agriculture Organization of the United Nations (FAO) within the PAAT framework (FAO, 2021). The Atlas is a dynamic database including geographical and epidemiological data, compiled by the WHO through the contribution of SSNCPs, NGOs and research institutes.

In 2014, a coordination network for human African trypanosomiasis was established under WHO leadership to ensure strengthened and sustained efforts to eliminate the disease. The stakeholders include national sleeping sickness control programmes, groups developing new tools to fight the disease, international and NGOs, and donors (WHO, 2020).