University of Glasgow, College of Medical, Veterinary and Life Sciences, Garscube Campus, Bearsden Road, Glasgow G61 1QH, UK.
Int J Parasitol. 2011 Feb;41(2):193-203. doi: 10.1016/j.ijpara.2010.08.004. Epub 2010 Sep 15.
The tick-borne apicomplexan parasite Theileria annulata is endemic in many sub-tropical countries and causes the bovine disease tropical theileriosis. Although the parasite is known to be highly diverse, detailed information is lacking on the genetic structure of natural populations and levels of multiplicity of infection in the cattle host. With the widespread deployment of live attenuated vaccines and the emergence of drug-resistant parasites in the field, it is vital to appreciate the factors which shape genetic diversity of the parasite both within individual hosts and in the wider population. This study addresses these issues and represents an extensive genetic analysis of T. annulata populations in two endemic countries utilising a high-throughput adaptation of a micro- and mini-satellite genotyping system. Parasite material was collected from infected cattle in defined regions of Turkey and Tunisia to allow a variety of analyses to be conducted. All animals (n=305) were found to harbour multiple parasite genotypes and only two isolates shared an identical predominant multi-locus profile. A modelling approach was used to demonstrate that host age, location and vaccination status play a measurable role in determining multiplicity of infection in an individual animal. Age was shown to positively correlate with multiplicity of infection and while positive vaccination status exerted a similar effect, it was shown to be due not simply to the presence of the immunising genotype. Importantly, no direct evidence was found for the immunising genotype spreading or recombining within the local parasite community. Genetic analysis confirmed the tentative conclusion of a previous study that the parasite population appears to be, in general, panmictic. Nevertheless, evidence supporting linkage disequilibrium and a departure from panmixia was uncovered in some localities and a number of explanations for these findings are advanced.
蜱传边缘无体寄生虫泰勒虫在许多亚热带国家流行，引起牛的热带泰勒虫病。尽管已知该寄生虫具有高度多样性，但对其自然种群的遗传结构和牛宿主感染的多重性水平的详细信息却知之甚少。随着活减毒疫苗的广泛应用和田间耐药寄生虫的出现，了解塑造寄生虫在个体宿主内和更广泛种群中的遗传多样性的因素至关重要。本研究解决了这些问题，并利用一种高通量微卫星和小型卫星基因分型系统的改编，对两个流行国家的泰勒虫种群进行了广泛的遗传分析。从土耳其和突尼斯的感染牛中采集寄生虫材料，以允许进行各种分析。所有动物（n=305）均携带多种寄生虫基因型，只有两种分离株具有相同的主要多位点图谱。一种建模方法表明，宿主年龄、位置和疫苗接种状态在决定个体动物的感染多重性方面起着可衡量的作用。年龄与感染的多重性呈正相关，而阳性疫苗接种状态也有类似的效果，但这并不是由于免疫基因型的存在。重要的是，没有直接证据表明免疫基因型在当地寄生虫群体中传播或重组。遗传分析证实了之前一项研究的初步结论，即寄生虫群体总体上似乎是泛交配的。然而，在一些地方发现了支持连锁不平衡和偏离泛交配的证据，并提出了一些对这些发现的解释。
