Sleeping sickness

Updated - August 2026

What are the causes?

Sleeping sickness occurs when the parasite Trypanosoma brucei gambiense (West Africa) or Trypanosoma brucei rhodesiense (East Africa) is introduced into the body following a bite from an infected tsetse fly. Tsetse flies become infected by biting humans or animals carrying the parasite.
Tsetse flies are only found in sub-Saharan Africa, and only some species transmit the parasite. Male and female tsetse flies feed exclusively on blood, on average every 3 to 4 days. They transmit the parasite to humans, livestock and some wild animals.

How is the parasite transmitted?

The parasite is mainly transmitted through a bite from an infected tsetse fly.

Trypanosomes are only transmitted in specific rural ecological niches. Many regions with tsetse fly populations do not experience sleeping sickness, probably because of the complex parasite development cycle in tsetse flies and their relatively low infection rate, even in endemic areas.

What are the symptoms?

During the first stage of the disease, the parasites in the blood and lymph system cause a range of general symptoms that make diagnosis difficult, such as fever, headache, tiredness and inflammation of the lymph nodes. In the absence of treatment, the parasites invade the central nervous system. In this second stage of the disease, symptoms include characteristic disruption of the sleep-wake cycle. The damage to the central nervous system is fatal if left untreated. 
During both stages of the disease, the trypanosomes also invade the tissues of some organs such as the skin, often causing widespread itching.
94% of sleeping sickness cases are caused by Trypanosoma brucei gambiense, which results in chronic infection – sufferers can be infected for several months or even years without showing severe symptoms. When symptoms are eventually linked with the disease, it is often already at an advanced stage and the central nervous system is already affected.

How is sleeping sickness diagnosed?

Whether or not clinical suspicion has been raised, diagnosis involves three successive steps: (1) screening via a serological test (CATT or RDT), (2) parasitological confirmation by microscopy to observe the live parasites in the blood or plasma or via lymph node puncture, generally after centrifugation or concentration, and (3) microscopic examination of cerebrospinal fluid obtained by lumbar puncture to see whether the parasites have reached the central nervous system (second stage) and adjust treatment as needed.

What treatments are available?

The type of treatment depends on the parasite species and how advanced the disease is, but the earlier the diagnosis, the better the prognosis. The drugs used during the first stage have few side effects and are relatively easy to administer: pentamidine or fexinidazole for Trypanosoma brucei gambiense, suramine or fexinidazole for Trypanosoma brucei rhodesiense. Treatment in the second stage is longer, more complex and potentially toxic as the drugs have to cross the blood-brain barrier. Melarsoprol (derived from arsenic) is effective against Trypanosoma brucei rhodesiense but kills 5 to 10% of patients from encephalopathy. Nifurtimox-eflornithine combination therapy (NECT) is effective and recommended for chronic advanced forms caused by Trypanosoma brucei gambiense. Fexinidazole, an effective oral drug with a shorter treatment regimen, has been available since 2020 for both stages of Trypanosoma brucei gambiense, and acoziborole, a single-dose oral treatment currently in clinical trials, could be a vital tool in eliminating the disease (zero transmission) by 2030, in line with the WHO target.

How can sleeping sickness be prevented?

There is no prophylaxis for sleeping sickness, but vector control measures, especially the use of blue or black fabric panels impregnated with residual insecticide, have proven highly effective in reducing tsetse fly populations and limiting transmission.

How many people are affected?

Africa has experienced major outbreaks, with peaks in 1930 and 2000. Current prevalence varies from one region to the next, although more than 60% of reported cases are in the Democratic Republic of the Congo and some countries have reported no cases for more than a decade.
Sustained efforts have led to a reduction in the number of cases since the 1990s. In 2018, just 977 new cases were reported. Since then, the official figures have remained below the threshold of a thousand new cases per year, but it is thought that the actual number of cases could be higher. Social instability and/or lack of access to diagnosis and treatment make it hard to establish an accurate overview of the situation and manage cases effectively. Around 30 million people are at risk of sleeping sickness in 29 sub-Saharan African countries.