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Human African trypanosomiasis (HAT), or sleeping sickness, is caused by two subspecies of a single-celled parasite, Trypanosoma brucei, and spread by the bite of the tsetse fly. The two forms behave very differently:
| T.b. gambiense | T.b. rhodesiense | |
|---|---|---|
| Where | West and central Africa | East and south Africa |
| Course | slow, over months to years | acute, over weeks |
The gambiense form accounts for about 92% of HAT cases worldwide, but the rhodesiense form is often the one that infects short-term travelers. Its reservoirs are domestic cattle and several big-game animals. In its first stage, the parasite multiplies in the blood and lymphatic system, causing fever, destruction of red blood cells and anemia, low platelet counts, an enlarged liver and spleen, and kidney disease. In the second stage it crosses into the brain and central nervous system, and death follows within weeks to months. About 90% of cases are fatal without treatment, so finding the parasite quickly and treating early are critical.
T.b. rhodesiense is endemic in 13 countries. Reported cases have fallen steadily since 2011, to only 24 in 2023, and published reports describe fewer than 30 cases in short-term travelers from countries without the disease over that period. Because the parasite lives in animals, the goal is to eliminate it as a public health problem rather than to stop transmission altogether, so occasional human cases and small outbreaks remain possible.
The case
In August 2024, CDC was consulted about a 57-year-old U.S. traveler who had recently returned from a safari in the Zambezi Valley in northern Zimbabwe. About two weeks after the likely exposure, he went to a U.S. hospital with two days of fever and a sharply outlined, ulcerated sore on his left thigh. He had no neurologic symptoms. A blood smear taken to rule out malaria showed trypanosomes, which CDC's reference laboratory confirmed as Trypanosoma brucei. His symptoms and travel fit rhodesiense HAT.
Following updated 2024 World Health Organization (WHO) guidelines, doctors started oral fexinidazole, which the guidelines now recommend for both stages of rhodesiense HAT. The patient quickly developed multisystem organ failure and needed dialysis, and a breathing tube for respiratory distress caused by fluid overload. Because it was uncertain how well fexinidazole would be absorbed through a feeding tube, doctors added intramuscular pentamidine, an alternative drug for first-stage disease. Suramin, the standard first-stage treatment before the 2024 guidelines, is generally avoided when the kidneys are impaired.
His neurologic function stayed at baseline throughout. Very low platelet counts, a known complication of the disease, made a lumbar puncture too risky, so doctors could not confirm that the parasite had not reached his central nervous system. After 10 days of pentamidine and fexinidazole he went home with only mild kidney dysfunction, and six months after discharge he showed no sign of relapse. Because parasite levels are high in this form of HAT and treatment can miss some, WHO recommends follow-up at 3, 6 and 12 months.
More cases from the same valley
Between August 2024 and January 2025, WHO received reports of three more rhodesiense HAT cases in people from countries without the disease who were bitten by tsetse flies while traveling in the Zambezi Valley. The valley spans northern Zimbabwe and southern Zambia, where conditions are similar and the parasite is endemic. These four were the first cases tied to the Zambezi Valley since 2019, although Zambia has had human cases elsewhere in that time.
What clinicians should do
- Think urgently of rhodesiense HAT in any traveler with fever arriving from an area where the parasite is endemic, even if that area has reported no recent cases.
- Order a peripheral blood smear promptly to look for trypanosomes; delay can be fatal.
- Treat with fexinidazole under the 2024 WHO guidelines, with frequent follow-up afterward.
- For help with diagnosis or treatment, contact CDC at parasites@cdc.gov or +1-404-718-4745.
Sources
- Wendt EM, Tobolowsky FA, Priotto G, Franco JR, Chancey R. Notes from the Field: Rhodesiense Human African Trypanosomiasis (Sleeping Sickness) in a Traveler Returning from Zimbabwe — United States, August 2024. MMWR Morb Mortal Wkly Rep 74(9). https://www.cdc.gov/mmwr/volumes/74/wr/mm7409a3.htm
Licence : CC0 1.0 (domaine public) · Adapté de www.cdc.gov
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