Most Americans planning a summer safari in Zambia or Zimbabwe are thinking about malaria prophylaxis, yellow fever vaccination, and what camera lens to pack. Very few are thinking about tsetse flies — or the potentially fatal parasitic disease those flies can transmit in a single bite. The CDC maintains an active travel notice for East African Sleeping Sickness in Zambia and Zimbabwe, warning that several cases of East African human trypanosomiasis have occurred in travelers returning from safari areas in these countries — a resurging cluster that includes the first documented U.S. case from the Zambezi Valley since 2019.
East African Human African Trypanosomiasis (HAT), caused by the parasite Trypanosoma brucei rhodesiense and transmitted by infected tsetse flies, is classified as a neglected tropical disease and is invariably fatal without treatment. Unlike West African trypanosomiasis — which causes a slow, years-long progression toward neurological deterioration and the characteristic somnolence that gave sleeping sickness its name — the East African (Rhodesiense) form progresses in weeks to months. Left untreated, patients develop neurological involvement within days to weeks of the bloodstream stage and can die within weeks to months of the initial infection.
The details of the case that re-established Zambezi Valley as an active transmission zone are documented in a CDC MMWR report published in 2025: a U.S. traveler returning from a wildlife area in Zimbabwe in August 2024 developed fever, fatigue, headache, and skin rash — symptoms that many physicians would attribute to malaria, dengue, or a non-specific viral illness — before eventually receiving the correct diagnosis and life-saving treatment. Three additional cases in travelers from other non-endemic countries who visited the same Zambezi Valley region were subsequently reported to the WHO, confirming that this was not an isolated event but an emerging cluster in a region that had been quiet for five years.
How Tsetse Flies Transmit African Trypanosomiasis — and Why They Are Hard to Avoid
Tsetse flies (genus Glossina) are found exclusively in sub-Saharan Africa, inhabiting woodland and bush areas near water sources. Unlike mosquitoes, which are attracted primarily to the chemical signatures of human skin and breath, tsetse flies are attracted to movement and to large dark-colored objects — which means they frequently bite wildlife, domesticated animals, safari vehicles, and the humans inside them. They are aggressive biters that can penetrate clothing, and their bites are painful enough to be noticed, which distinguishes them from the painless mosquito bite of malaria transmission.
The CDC's recommendations for safari travelers to endemic areas specifically address tsetse fly avoidance: wear medium-weight, neutral-colored clothing (khaki, tan, olive), including long-sleeved shirts and long pants; avoid wearing blue or very dark colors (to which tsetse flies are strongly attracted); inspect vehicles and clothing before boarding; use insect repellent; and avoid dense bush and woodland near water during the hours of peak tsetse activity (morning and late afternoon).
The Zambezi Valley, which spans northern Zimbabwe and southern Zambia, is a documented historical endemic zone for T. brucei rhodesiense, and the 2024 cluster of cases after a five-year gap from that specific area suggests that transmission conditions have re-established — possibly as wildlife populations recover from previous disruptions, or as tsetse habitats shift with changing land use and climate patterns.
What Makes Diagnosis So Critical — and So Frequently Delayed
The initial symptoms of East African HAT — fever, severe headache, fatigue, muscle aches, joint pain, and a red sore (chancre) at the bite site — appear 1 to 3 weeks after infection and are clinically indistinguishable from malaria, influenza, or multiple other tropical and non-tropical illnesses. Many travelers will have received malaria chemoprophylaxis that prevents malaria but offers no protection against trypanosomiasis, and when malaria tests return negative, sleeping sickness may not immediately appear on the differential diagnosis of emergency physicians or general practitioners who have never encountered the disease.
The key diagnostic test is a peripheral blood smear examined under microscopy for the presence of trypanosomes — the elongated, motile parasites that are visible in blood during the early bloodstream stage of the disease. This test requires an experienced microscopist and may require multiple samples examined at peak parasitemia. Given the disease's rapid progression, any traveler with fever returning from a Zambia or Zimbabwe safari who tests negative for malaria should have sleeping sickness specifically excluded through peripheral blood smear, and clinicians who suspect the diagnosis should contact the CDC Emergency Operations Center at (770) 488-7100 for assistance with testing and treatment guidance.
Treatment of early-stage East African HAT uses suramin, an intravenous drug that must be obtained through the CDC. Late-stage disease with neurological involvement requires nifurtimox-eflornithine combination therapy (NECT), also available through the CDC. Both require prompt recognition and immediate treatment consultation.
Frequently Asked Questions
Q: What is East African Sleeping Sickness?
A: East African Human African Trypanosomiasis (HAT) is a parasitic disease caused by Trypanosoma brucei rhodesiense, transmitted by tsetse fly bites in sub-Saharan Africa. Without treatment, it is uniformly fatal, and can cause death within weeks to months.
Q: Why are Zambia and Zimbabwe specifically a concern right now?
A: A cluster of cases occurred in the Zambezi Valley region — spanning northern Zimbabwe and southern Zambia — in 2024, including a U.S. traveler and three other non-endemic country travelers. These are the first Zambezi Valley-linked cases since 2019, indicating re-establishment of active transmission in that region.
Q: How can safari travelers protect themselves from tsetse flies?
A: Wear neutral-colored medium-weight clothing (khaki, tan, olive), avoid blue or very dark colors, inspect vehicles before boarding, use insect repellent, and avoid dense bush near water during peak tsetse activity hours (morning and late afternoon).
Q: What should I do if I develop fever after a Zambia or Zimbabwe safari?
A: Seek emergency care immediately and disclose your safari travel history. Ask specifically that malaria AND African trypanosomiasis be considered and tested for. If malaria tests are negative and fever persists, peripheral blood smear for trypanosomes is the critical next test.
Q: How is East African sleeping sickness treated?
A: Early-stage disease uses suramin (IV). Late-stage neurological disease requires nifurtimox-eflornithine combination therapy (NECT). Both must be obtained through and administered with guidance from the CDC Emergency Operations Center.
