Trypanosomiasis

Unique identifier / Notation

BI0238

Synonyms

Sleeping sickness Human African trypanosomiasis HAT

Trypanosomiasis, human African (sleeping sickness) and animal trypanosomosis (nagana) are caused by protozoan parasites belonging to the genus Trypanosoma transmitted by infected tsetse flies and is endemic in sub-Saharan Africa. Without treatment, the disease is considered fatal (adapted from WHO, 2023 and FAO, no date).

Primary reference(s)

WHO, 2023. Trypanosomiasis, human African (sleeping sickness). World Health Organization (WHO). Accessed 27 May 2025.

FAO, no date. Programme Against African Trypanosomosis (PAAT). Food and Agriculture Organization of the United Nations (FAO). Accessed 27 May 2025.

Annotations

Additional scientific description

Human

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, 2023).

Tsetse flies are only found in sub-Saharan Africa and only certain species transmit the disease. 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, 2023).

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 92% of reported cases of sleeping sickness and causes infection (WHO, 2023).
T. brucei rhodesiense is found in 13 countries in eastern and southern Africa. This form accounts for 8% of reported cases and causes an acute disease. The disease develops rapidly and invades the central nervous system. Only Uganda presents both forms of the disease, but in separate zones (WHO, 2023).

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, 2023).

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, 2023).

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, 2023).

Currently, the disease incidence differs from one country to another as well as in different parts of a single country. In the past 5 years, over 61% of reported cases occurred in the Democratic Republic of the Congo (WHO, 2023).

Angola, Central African Republic, Chad, Congo, Gabon, Guinea, Malawi and South Sudan declared between 10 and 100 new cases in the last 5 years. Cameroon, Côte d'Ivoire, Equatorial Guinea, Kenya, Uganda, United Republic of Tanzania, Ethiopia and Zambia declared between 1 and 10 new cases in the last 5 years. Burkina Faso, Ghana, Kenya, Nigeria and Zimbabwe have reported sporadic cases in the last decade. Benin, Botswana, Burundi, Eswatini, Gambia, Guinea Bissau, Liberia, Mali, Mozambique, Namibia, Niger, Rwanda, Senegal, Sierra Leone 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, 2023).

Animal

Tsetse-transmitted animal trypanosomosis occurs in tropical regions of sub-Saharan Africa, where it constitutes a major obstacle to the development of animal production. The considerable economic and social repercussions make control of this disease a priority for the development of a large part of the African continent.

There are no effective vaccines commercially available against Trypanosomes.

• African animal trypanosomosis affects ruminants, swine, camels, equines, and carnivores, as well as a broad range of wild animals, but the heaviest economic burden is in cattle. In cattle, the disease is called Nagana.

• The disease is caused by several species of trypanosome but mainly by Trypanosoma congolense, T. vivax, T. brucei, and T. simiae. T. vivax is also present in Latin America, where in the absence of tsetse flies it is transmitted by other biting flies.

• A different species (i.e. T. evansi) is also present outside of Africa, including Asia.

• Trypanosomes have developed refined mechanisms to escape from the immune system by either changing their own "antigen appearance" and/or actively eliminating the B cell memory compartment (Marcelino, I. et al, 2021).

• Control and, where feasible, elimination of animal trypanosomosis as a disease with a zoonotic dimension would help to improve animal production in Africa considerably and would also contribute to enhancing human health (Diall et al., 2017).

• Transmission of trypanosomes by insects occurs through cyclical transmission or mechanical transmission.

• Cyclical transmission, during which the trypanosomes actively multiply in the vectors, occurs in sub-Saharan Africa through the intermediary of tsetse flies (Glossina spp.) (Cecchi et al., 2024). Mechanical transmission can be caused by various blood-sucking insects such as flies of the family Tabanidae (horse flies) and Stomoxys spp. (Diall et al., 2017).

• Animals can host the human pathogen parasites, especially T. brucei rhodesiense, of which domestic and wild animals are the most important reservoirs. Animals can also be infected with T. brucei gambiense and possibly act as a reservoir to some extent. However, the precise epidemiological role of the animal reservoir in the gambiense form of the disease is not yet well known (WHO, 2023).

• Trypanosomosis (tsetse-transmitted) is one of the World Organisation for Animal Health (WOAH) Listed diseases (WOAH, 2024)

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 Congo, and South Sudan. Sleeping sickness was the first or second greatest cause of mortality in those communities. After continued control efforts, HAT occurrence reached a historic low under 2,000 cases in 2017 and under 1,000 cases in 2018, remaining below that threshold as of 2022. The population at risk estimated for the period 2016–2020 was 55 million people, with only 3 million at moderate-high risk (WHO, 2023).

Key relevant UN convention / multilateral treaty

WHO. 2013. International Health Regulations (2005), 3rd ed. (WHO, 2016).

WTO Agreement on the Application of Sanitary and Phytosanitary Measures (SPS Agreement) (WTO, 1994).

Drivers

Human

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 has been reported once (WHO, 2023).

Animal

Presence/introduction of Trypanosoma infected tsetse fly.

Impacts

Human

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, 2023).

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 knownas the neurological or meningo-encephalic stage. In general, this is when more obvious signs and symptoms of the disease appear: changes in 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 rare cases of self-cure have been reported (WHO, 2023).

Animal

Mortality and morbidity of animals and humans, spread of infection.

Multi-hazard context

: Sleeping sickness affects people in rural areas of African countries (CDC, 2025). People at higher risk include:

Hunters
Villagers with infected cattle herds
Tourists visiting and others working in game parks

Tsetse flies that spread sleeping sickness live only in some African countries. Most flies in these rural areas are not carrying the parasite that causes sleeping sickness. However, the more often that you are bitten, the more you are at risk of infection (CDC, 2025).

Risk Management

Human

New WHO treatment guidelines for gambiense-HAT were issued in 2019 (WHO, 2023). 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 (WHO, 2023).

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

In 2008, the WHO launched the Atlas of human African Trypanosomiasis initiative to map at village-level all reported cases (WHO, no date b). This initiative is jointly implemented with the Food and Agriculture Organization of the United Nations (FAO) within the PAAT framework (FAO, 2021). The PAAT was officially established in November 1997 by the 29th Session of the FAO Conference (Resolution 5/97). The PAAT secretariat includes representatives of the Food and Agriculture Organization of the United Nations (FAO), the International Atomic Energy Agency (IAEA), the World Health Organization (WHO) and the African Union-Interafrican Bureau for Animal Resources (AU-IBAR) (FAO, 2025). Progressive Control Pathways (PCPs) and the related roadmaps are staged, stepwise approaches increasingly used to structure the road to disease reduction and freedom for a range of human and animal diseases, including foot-and-mouth disease (BI0306), peste des petits ruminants (BI0310), brucellosis (BI0202) and rabies (BI0232). The PCP for African Animal Trypanosomosis is developed and promoted by FAO within the framework of PAAT, and in collaboration with IAEA, AU-PATTEC and CIRAD.

The Atlas is a dynamic database including geographical and epidemiological data, compiled by the WHO through the contribution of SSNCPs, NGOs and research institutes (WHO, no date b).

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, 2023).

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021b).

WHO’s Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a natural disaster. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARS should re-integrate back into the national system (WHO, 2023).

Animal

Disease control for animal trypanosomosis includes treatment with trypanocides, vector control and strengthened surveillance (Diall et al., 2017).

Monitoring

The table below offers an overview of monitoring for trypanosomiasis and trypanosomosis. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.

Which institution(s) produce(s) Disaster Risk Data/Information?

WHO, Ministry of Health, FAO Reference Centres, WHO Collaborating Centres, WOAH Reference Centres,

How is the Hazard Observed/Monitored/Forecast?

FAO empres-i+ https://empres-i.apps.fao.org/diseases

WOAH WAHIS https://wahis.woah.org/#/event-management

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021b).

WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a natural disaster. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARSs should re-integrate back into the national system (WHO, no date, a).