The Roslin Institute, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Campus, Roslin, Midlothian EH25 9RG, UK.
The International Livestock Research Institute, PO Box 30709, Nairobi, Kenya.
Int J Parasitol. 2020 May;50(5):403-412. doi: 10.1016/j.ijpara.2019.12.006. Epub 2020 Feb 4.
The tick-borne protozoan parasite Theileria parva causes an acute, often fatal disease in cattle throughout a large part of eastern and southern Africa. Infection of African buffalo (Syncerus caffer) is also widespread in this region but does not cause clinical disease in this species. This difference most likely reflects the evolutionary history of the parasites in these species, in that cattle were only introduced into Africa within the last 8000 years. In both hosts, T. parva establishes a carrier state, involving persistence of small numbers of parasites for many months following the acute phase of infection. This persistence is considered important for maintaining the parasite populations. Although cattle and buffalo parasites both produce severe disease when transmitted to cattle, the buffalo-derived parasites are usually not transmissible from infected cattle. Recent studies of the molecular and antigenic composition of T. parva, in addition to demonstrating heterogeneity in the populations in both host species, have revealed that infections in individual animals are genotypically mixed. The results of these studies have also shown that buffalo T. parva exhibit much greater genotypic diversity than the cattle population and indicate that cattle parasites represent a subpopulation of T. parva that has adapted to maintenance in cattle. The parasites in cattle and buffalo appear to be maintained largely as separate populations. This insight into the genotypic composition of T. parva populations has raised important questions on how host adaptation of the parasite has evolved and whether there is scope for further adaptation of buffalo-maintained populations to cattle.
在东非和南非的大部分地区，蜱传播的原生动物寄生虫泰勒虫会导致牛群出现急性、往往致命的疾病。在该地区，非洲野牛（Syncerus caffer）也广泛受到感染，但这种疾病在该物种中不会引起临床症状。这种差异很可能反映了这些物种中寄生虫的进化历史，因为牛只在过去 8000 年内才被引入非洲。在这两种宿主中，T. parva 建立了一种带虫状态，在感染的急性阶段之后，少量寄生虫会持续存在数月。这种持续存在被认为对维持寄生虫种群很重要。尽管牛和水牛的寄生虫在传播给牛时都会导致严重疾病，但源自水牛的寄生虫通常不能从感染的牛传播。最近对 T. parva 的分子和抗原组成的研究，除了证明两种宿主物种中的寄生虫群体存在异质性外，还表明个体动物的感染是基因型混合的。这些研究的结果还表明，水牛 T. parva 的基因型多样性比牛群大得多，表明牛寄生虫代表了适应在牛群中维持的 T. parva 的一个亚群。牛和水牛中的寄生虫似乎主要作为独立的群体得到维持。对 T. parva 群体基因型组成的这种深入了解引发了一些重要问题，即寄生虫对宿主的适应是如何进化的，以及水牛维持的种群是否有进一步适应牛的空间。
