A clinical and epidemiological investigation of the first reported human infection with the zoonotic parasite Trypanosoma evansi in Southeast Asia


Background.Trypanosoma is a genus of unicellular parasitic flagellate protozoa. Trypanosome brucei spp. and Trypanosoma cruzi are the major agents of human trypanosomiasis; other Trypanosoma spp. can cause human disease, but are rare. In March 2015 a 38-year-old woman presented to a healthcare facility in southern Vietnam with fever, headache and arthralgia. Microscopic examination of blood revealed a trypanosoma infection.

Image/United States Army Center of Military History
Image/United States Army Center of Military History

Methods. Microscopic observation, PCR amplification of blood samples and serological testing were performed to identify the infecting species. The patient’s blood was screened for the trypanocidal protein Apolipoprotein L1 and a field investigation was performed to identify the zoonotic source.

Results. PCR amplification and serological testing identified the infecting species as Trypanosoma evansi. Despite relapsing six weeks after completing amphotericin B therapy, the patient made a complete recovery after five weeks of suramin. The patient was found to have two wild-typeAPOL1 alleles and a normal serum Apolipoprotein L1 concentration. After responsive animal sampling in the presumed location of exposure, cattle and/or buffalo were the most likely source of the infection, with 14/30 (47%) of animal blood samples testing PCR positive for Trypanosoma evansi.

Conclusions. We report the first laboratory confirmed case of Trypanosoma evansi in a previously healthy individual without APOL1 deficiency, potentially contracted via a wound whilst butchering raw beef, and successfully treated with suramin. A linked epidemiological investigation revealed widespread and previously unidentified burden of Trypanosoma evansi in local cattle, highlighting the need for surveillance of this infection in animals and the possibility of further human cases.