Human African trypanosomiasis (sleeping sickness): Parasitic disease transmitted by tsetse flies
Sleeping sickness: Deadly parasitic disease nearing elimination in Africa
Dr. Emmanuel Kabanga (Kasansa Health Zone, Democratic Republic of Congo) remembers his first sleeping sickness patient in 1998. A young woman named Marie, 24 years old, mother of two small children. She arrived at the rural clinic barely conscious, unable to walk, speaking incoherently.
“Her husband carried her on his back for three days through the forest to reach our clinic,” Dr. Kabanga recalled, his voice still heavy with emotion decades later. “He said she’d been sick for months—first fever and headaches, then she stopped sleeping at night but couldn’t stay awake during the day. She became confused, stopped recognizing her children, couldn’t eat. She was dying.”
Dr. Kabanga recognized the symptoms immediately: Human African trypanosomiasis (HAT), or sleeping sickness. The parasites had already invaded Marie’s brain. Without treatment, she had days to live. Back then, the only available treatment for advanced sleeping sickness was melarsoprol—an arsenic-based drug so toxic it killed 5% of patients during treatment.
“I had to tell her husband that the treatment might kill her, but without it, she would certainly die,” Dr. Kabanga explained. “He begged me to try. We had no choice.” Marie survived the treatment. After three months of recovery, she walked home to her children. But many others weren’t so fortunate.
According to WHO, Human African trypanosomiasis (HAT), or sleeping sickness, is caused by trypanosome parasites that are transmitted by tsetse flies. HAT is found only in sub-Saharan Africa. Two subspecies of Trypanosoma brucei cause disease: T. b. gambiense in West and Central Africa, and T. b. rhodesiense in East Africa.
For more on parasitic diseases, see our articles on leishmaniasis and Chagas disease at ObserverVoice.com. WHO provides comprehensive fact sheet on Trypanosomiasis, human African (sleeping sickness) and Frequently asked questions on sleeping sickness.
Disease Affecting Poor Rural Communities
This life-threatening disease mostly affects poor rural populations, causing significant harm. Travellers to endemic regions may also be at risk of infection. HAT transmission requires the interaction of humans, tsetse flies and parasite reservoirs (humans, and domestic and wild animals). The animal reservoir is very important in T. b. rhodesiense and less so in T. b. gambiense, although it could explain the long-term endemicity in some foci despite control interventions.
Transmission can be interrupted by depleting the parasite reservoirs through detection and treatment of infected people and/or domestic animals and by reducing the tsetse fly population and human–tsetse contact. In 1995, about 25,000 cases were detected, 300,000 undetected cases were estimated and 60 million people were estimated to be at risk of HAT infection. In 2001, WHO launched an initiative to reinforce control and surveillance, and HAT decreased markedly in the ensuing years. Since 2019, fewer than 1,000 cases are reported yearly. This reduction does not reflect a lack of control efforts as in general active and passive screening has been maintained at similar levels (around 2.5 million people screened per year).
WHO provides databases on Distribution in disease-endemic countries, Risk of human African trypanosomiasis, Interactive graph for HAT, Number of reported cases (T.b. gambiense), and Number of reported cases (T.b. rhodesiense).
Related topics include Chagas disease (American trypanosomiasis), Dracunculiasis (Guinea-worm disease), Leishmaniasis, and Leprosy (Hansen disease). For more on neglected tropical diseases, see our article on disease elimination efforts at ObserverVoice.com.
Two-Stage Progression with Devastating Symptoms
After infection, trypanosomes multiply in the blood and lymph (first-stage, haemolymphatic) and, following a variable incubation period (from days to months), unspecific symptoms and signs such as headache, fever, weakness, joint pain, and lymphadenopathy appear. Over time, the parasites cross the blood–brain barrier to invade the central nervous system (second-stage, meningoencephalitic), causing various neurological disturbances including sleep disorders (excessive daytime sleepiness, nocturnal insomnia), deep sensory disturbances, abnormal movements, tremor, ataxia, walking difficulties, speech difficulties, psychiatric disorders, seizures, coma and ultimately death. Most signs and symptoms are common to both stages, and sleep disorders in particular can appear already during the first stage.
Rhodesiense HAT is typically acute, progressing to second-stage within a few weeks, and to death within 6 months. Gambiense HAT progresses slowly over around 3 years (highly variable). An inoculation chancre (dermal reaction of 3–4 cm at the tsetse bite site) may appear 2–3 days after infection with rhodesiense HAT in up to 25% of local patients, but more frequently in patients from non-endemic regions. It is rare with gambiense HAT.
Sleeping sickness is diagnosed in several steps: after a clinical suspicion, serological tests (card agglutination trypanosomiasis test or HAT rapid diagnostic tests) can reinforce the suspicion, which should be confirmed by parasitological findings (in chancre exudate, lymphatic juice, blood and cerebrospinal fluid). Unfortunately, the usual serological tests are only applicable to T. b. gambiense. Stage is determined by the number of white blood cells and the presence of trypanosomes in cerebrospinal fluid examination.
Treatment Options Dramatically Improved
All confirmed HAT cases require treatment. Available treatment can cure most patients, completely eliminating trypanosomes from the body. Treatment of cases suspected by serology depends on specific conditions set by national protocols, which usually set specific conditions defining a higher suspicion index. The current treatment options include six medicines, all of which are donated by the manufacturers; WHO ensures their worldwide distribution free of charge.
Treatment choices are based on the causative trypanosome and the disease stage. The medicines for treatment of second-stage must cross the blood–brain barrier and tend to be more toxic and complex to administer than first-stage medicines. In 2019, WHO issued interim guidelines for treatment of gambiense HAT. For treatment of rhodesiense HAT, the former guidelines remain valid.
Gambiense HAT can be treated with oral fexinidazole in first-stage and also non-severe second-stage, with some limitations of age and body weight and following some important specific rules to ensure efficacy. In first-stage, intramuscular pentamidine can be also used, and in second stage nifurtimox–eflornithine combination therapy (NECT). Rhodesiense HAT must be treated without delay, because it can provoke multi-organ failure and progress to second stage within a few weeks. In first-stage, the treatment is intravenous suramin, with pentamidine as an alternative. In second-stage, the only treatment is intravenous melarsoprol.
Recent WHO Initiatives and Achievements
June 2024 WHO published Guidelines for the treatment of human African trypanosomiasis providing updated evidence-based recommendations on therapeutic choices. May 2024 WHO published Human African trypanosomiasis eliminated as a public health problem in Chad. November 2025 WHO announced WHO and Bayer AG renew longstanding collaboration to eliminate three deadly neglected tropical diseases. August 2025 WHO announced Kenya achieves elimination of human African trypanosomiasis or sleeping sickness as a public health problem. February 2025 WHO delivers fexinidazole to Malawi and Zimbabwe – a long-awaited safer treatment for rhodesiense human African trypanosomiasis. January 2025 WHO announced Guinea eliminates human African trypanosomiasis as a public health problem.
WHO activities include Mapping and tracking transmission until elimination, Coordinating partners and countries within one HAT network, Supporting research and innovation, and Supporting endemic countries to eliminate. WHO’s Control of Neglected Tropical Diseases programme coordinates global efforts.
Strong Global Commitment
World Health Assembly passed WHA57.2 on Control of human African trypanosomiasis, 2004, WHA56.7 on Pan African Tsetse and trypanosomiasis eradication campaign, 2003, WHA50.36 on African trypanosomiasis, 1997, and WHA36.31 on African human trypanosomiasis, 1983.
Dr. Kabanga now works in a world transformed. “In 1998, I saw dozens of sleeping sickness cases every year. Many died despite treatment. Today, I see maybe one or two cases annually. The new oral medicine, fexinidazole, changed everything—patients can take pills at home instead of receiving toxic intravenous infusions in hospitals for weeks.”
“But the greatest transformation is prevention. Mobile screening teams visit remote villages, testing entire populations. They find cases early, before the parasites reach the brain. Early treatment is simple, safe, highly effective,” Dr. Kabanga emphasized. “We’re on the verge of eliminating sleeping sickness as a public health problem. Countries like Kenya and Guinea have already achieved this milestone. It seemed impossible in 1998 when we were losing so many patients. Now it’s within reach.”
“What made the difference? Political commitment, sustained funding, donated medicines from pharmaceutical companies, dedicated health workers, innovative diagnostic tools, safer treatments, and comprehensive surveillance,” Dr. Kabanga explained. “Sleeping sickness proves that even the most devastating neglected tropical diseases can be defeated. We just need to maintain the effort until every last case is eliminated. We cannot stop now when we’re so close to victory.”
For more information, visit WHO’s sleeping sickness topic page or explore related content at ObserverVoice.com.
Frequently Asked Questions (FAQs)
Human African trypanosomiasis (HAT), or sleeping sickness, is caused by trypanosome parasites that are transmitted by tsetse flies. HAT is found only in sub-Saharan Africa. Two subspecies of Trypanosoma brucei cause disease: T. b. gambiense in West and Central Africa, and T. b. rhodesiense in East Africa. This life-threatening disease mostly affects poor rural populations, causing significant harm. Travellers to endemic regions may also be at risk of infection. HAT transmission requires interaction of humans, tsetse flies and parasite reservoirs (humans, and domestic and wild animals). Animal reservoir is very important in T. b. rhodesiense and less so in T. b. gambiense. Transmission can be interrupted by depleting parasite reservoirs through detection and treatment of infected people and/or domestic animals and by reducing tsetse fly population and human–tsetse contact. In 1995, about 25,000 cases were detected, 300,000 undetected cases were estimated. Since 2019, fewer than 1,000 cases are reported yearly. WHO provides Distribution in disease-endemic countries, Risk map. WHO fact sheet: Sleeping sickness.
After infection, trypanosomes multiply in blood and lymph (first-stage, haemolymphatic) and, following variable incubation period (from days to months), unspecific symptoms such as headache, fever, weakness, joint pain, lymphadenopathy appear. Over time, parasites cross blood–brain barrier to invade central nervous system (second-stage, meningoencephalitic), causing various neurological disturbances including sleep disorders (excessive daytime sleepiness, nocturnal insomnia), deep sensory disturbances, abnormal movements, tremor, ataxia, walking difficulties, speech difficulties, psychiatric disorders, seizures, coma and ultimately death. Most signs and symptoms are common to both stages, and sleep disorders can appear already during first stage. Rhodesiense HAT is typically acute, progressing to second-stage within few weeks, and to death within 6 months. Gambiense HAT progresses slowly over around 3 years (highly variable). Inoculation chancre (dermal reaction of 3–4 cm at tsetse bite site) may appear 2–3 days after infection with rhodesiense HAT in up to 25% of local patients. WHO Q&A: Sleeping sickness FAQ. Related: Chagas disease, Leishmaniasis.
Sleeping sickness is diagnosed in several steps: after clinical suspicion, serological tests (card agglutination trypanosomiasis test or HAT rapid diagnostic tests) can reinforce suspicion, which should be confirmed by parasitological findings (in chancre exudate, lymphatic juice, blood and cerebrospinal fluid). Unfortunately, usual serological tests are only applicable to T. b. gambiense. Stage is determined by number of white blood cells and presence of trypanosomes in cerebrospinal fluid examination. WHO provides Interactive graph for HAT, Number of reported cases (T.b. gambiense), Number of reported cases (T.b. rhodesiense). WHO activities: Mapping and tracking transmission, Supporting research and innovation. Related: Dracunculiasis, Leprosy.
All confirmed HAT cases require treatment. Available treatment can cure most patients, completely eliminating trypanosomes from body. Current treatment options include six medicines, all donated by manufacturers; WHO ensures their worldwide distribution free of charge. Treatment choices are based on causative trypanosome and disease stage. Medicines for treatment of second-stage must cross blood–brain barrier and tend to be more toxic and complex to administer than first-stage medicines. In 2019, WHO issued interim guidelines for treatment of gambiense HAT. For rhodesiense HAT, former guidelines remain valid. Gambiense HAT can be treated with oral fexinidazole in first-stage and non-severe second-stage. In first-stage, intramuscular pentamidine can also be used, and in second stage nifurtimox–eflornithine combination therapy (NECT). Rhodesiense HAT must be treated without delay. In first-stage, treatment is intravenous suramin, with pentamidine as alternative. In second-stage, only treatment is intravenous melarsoprol. June 2024 WHO published Guidelines for treatment. February 2025 WHO delivers fexinidazole to Malawi and Zimbabwe.
In 1995, about 25,000 cases were detected, 300,000 undetected cases estimated, 60 million people at risk. In 2001, WHO launched initiative to reinforce control and surveillance, and HAT decreased markedly. Since 2019, fewer than 1,000 cases reported yearly. August 2025 WHO announced Kenya achieves elimination as public health problem. January 2025 WHO announced Guinea eliminates as public health problem. May 2024 WHO published Chad eliminated as public health problem. November 2025 WHO announced WHO and Bayer AG renew collaboration to eliminate three deadly NTDs. WHO activities: Coordinating partners within one HAT network, Supporting endemic countries to eliminate. WHA passed WHA57.2 on Control, 2004, WHA56.7 on Pan African eradication campaign, 2003. WHO’s Control of Neglected Tropical Diseases coordinates efforts.
- WHO Sleeping Sickness Topic Page
- WHO Fact Sheet on Sleeping Sickness
- WHO Guidelines for Treatment of HAT
- Interactive HAT Data
- WHO Control of Neglected Tropical Diseases
Disclaimer: This article is an adaptation of publicly available information from WHO’s Human African trypanosomiasis health topic page (WHO, Geneva. Licence: CC BYNC-SA 3.0 IGO). WHO is not responsible for the content or accuracy of this adaptation. This content is for informational and educational purposes
only and does not constitute medical advice. ObserverVoice.com is a news and information platform
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