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.

埃文西锥虫是引起 surra 的寄生虫，是骆驼和其他牲畜中的一种锥虫病，在肯尼亚和世界许多其他地区造成严重的经济负担。伊氏锥虫的传播可以通过 tabanid 和 Stomoxys 叮咬苍蝇来机械地维持，而密切相关的非洲锥虫T . brucei brucei和T。乙。罗得西亚需要采采蝇（舌蝇属）的周期性发育才能传播。在这项研究中，我们调查了T的进化起源。埃文西. 我们使用 15 个多态微卫星来量化 41 T中遗传多样性的水平和模式。evansi分离株和 66 个T分离株。乙。brucei (n = 51) 和T。乙。罗得西亚（n = 15），包括许多来自肯尼亚的地区，T . 埃文西可能是从T进化而来的。布鲁塞_ 我们发现T . evansi菌株属于至少两个不同的T。brucei基因单位和包含与吨。brucei菌株。结果表明 41 T . evansi分离株源自多个T。来自不同遗传背景的brucei菌株，暗示T的独立起源。来自T的埃文西。brucei菌株。这一令人惊讶的发现进一步表明获得了T的能力。evansi以机械方式传播，从而摆脱与非洲采采蝇媒介的必然联系的能力，反复发生。这些发现，如果得到证实，具有流行病学意义，如T。来自不同遗传背景的布氏菌株可能成为危险的、世界性的牲畜疾病或致命的人类疾病的病原体，如T . 乙。罗得西亚