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PLoS Negl Trop Dis. 2017 Sep 7;11(9):e0005895. doi: 10.1371/journal.pntd.0005895. eCollection 2017 Sep.

Multiple evolutionary origins of Trypanosoma evansi in Kenya.

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Biotechnology Research Institute, Kenya Agricultural and Livestock Research Organization, Kikuyu, Kenya.
Department of Biomedical Sciences and Technology, School of Public Health and Community Development, Maseno University, Maseno, Kenya.
Yale School of Public Health, Department of Epidemiology of Microbial Diseases, New Haven, CT, United States of America.
Department of Ecology & Evolutionary Biology, Yale University, New Haven, CT, United States of America.
Centre for Geographic Medicine Research Coast, Kenya Medical Research Institute, Kilifi, Kenya.
Centre for Immunity, Infection & Evolution, and Institute of Immunology & Infection Research, University of Edinburgh, Edinburgh, Scotland, United Kingdom.


Trypanosoma evansi is the parasite causing surra, a form of trypanosomiasis in camels and other livestock, and a serious economic burden in Kenya and many other parts of the world. Trypanosoma evansi transmission can be sustained mechanically by tabanid and Stomoxys biting flies, whereas the closely related African trypanosomes T. brucei brucei and T. b. rhodesiense require cyclical development in tsetse flies (genus Glossina) for transmission. In this study, we investigated the evolutionary origins of T. evansi. We used 15 polymorphic microsatellites to quantify levels and patterns of genetic diversity among 41 T. evansi isolates and 66 isolates of T. b. brucei (n = 51) and T. b. rhodesiense (n = 15), including many from Kenya, a region where T. evansi may have evolved from T. brucei. We found that T. evansi strains belong to at least two distinct T. brucei genetic units and contain genetic diversity that is similar to that in T. brucei strains. Results indicated that the 41 T. evansi isolates originated from multiple T. brucei strains from different genetic backgrounds, implying independent origins of T. evansi from T. brucei strains. This surprising finding further suggested that the acquisition of the ability of T. evansi to be transmitted mechanically, and thus the ability to escape the obligate link with the African tsetse fly vector, has occurred repeatedly. These findings, if confirmed, have epidemiological implications, as T. brucei strains from different genetic backgrounds can become either causative agents of a dangerous, cosmopolitan livestock disease or of a lethal human disease, like for T. b. rhodesiense.

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