Hall Carina M, Busch Joseph D, Scoles Glen A, Palma-Cagle Kristina A, Ueti Massaro W, Kappmeyer Lowell S, Wagner David M
Center for Microbial Genetics and Genomics, Northern Arizona University, Flagstaff, AZ 86011, USA.
Parasit Vectors. 2013 Feb 11;6:35. doi: 10.1186/1756-3305-6-35.
Theileria equi is a tick-borne apicomplexan hemoparasite that causes equine piroplasmosis. This parasite has a worldwide distribution but the United States was considered to be free of this disease until recently.
We used samples from 37 horses to determine genetic relationships among North American T. equi using the 18S rRNA gene and microsatellites. We developed a DNA fingerprinting panel of 18 microsatellite markers using the first complete genome sequence of T. equi.
A maximum parsimony analysis of 18S rRNA sequences grouped the samples into two major clades. The first clade (n = 36) revealed a high degree of nucleotide similarity in U.S. T. equi, with just 0-2 single nucleotide polymorphisms (SNPs) among samples. The remaining sample fell into a second clade that was genetically divergent (48 SNPs) from the other U.S. samples. This sample was collected at the Texas border, but may have originated in Mexico. We genotyped T. equi from the U.S. using microsatellite markers and found a moderate amount of genetic diversity (2-8 alleles per locus). The field samples were mostly from a 2009 Texas outbreak (n = 22) although samples from five other states were also included in this study. Using Weir and Cockerham's FST estimator (θ) we found strong population differentiation of the Texas and Georgia subpopulations (θ = 0.414), which was supported by a neighbor-joining tree created with predominant single haplotypes. Single-clone infections were found in 27 of the 37 samples (73%), allowing us to identify 15 unique genotypes.
The placement of most T. equi into one monophyletic clade by 18S is suggestive of a limited source of introduction into the U.S. When applied to a broader cross section of worldwide samples, these molecular tools should improve source tracking of T. equi outbreaks and may help prevent the spread of this tick-borne parasite.
马泰勒虫是一种蜱传播的顶复门血液寄生虫，可引起马焦虫病。这种寄生虫在全球范围内分布，但直到最近美国都被认为没有这种疾病。
我们使用来自37匹马的样本，利用18S rRNA基因和微卫星来确定北美马泰勒虫之间的遗传关系。我们利用马泰勒虫的首个完整基因组序列开发了一个由18个微卫星标记组成的DNA指纹图谱。
对18S rRNA序列进行的最大简约分析将样本分为两个主要分支。第一个分支（n = 36）显示美国马泰勒虫的核苷酸相似度很高，样本间仅有0 - 2个单核苷酸多态性（SNP）。其余样本属于第二个分支，与其他美国样本在基因上有差异（48个SNP）。该样本是在得克萨斯边境采集的，但可能起源于墨西哥。我们使用微卫星标记对来自美国的马泰勒虫进行基因分型，发现有中等程度的遗传多样性（每个位点2 - 8个等位基因）。现场样本大多来自2009年得克萨斯州的一次疫情（n = 22），不过本研究也包括了来自其他五个州的样本。使用韦尔和科克汉姆的FST估计值（θ），我们发现得克萨斯州和佐治亚州亚群有很强的种群分化（θ = 0.414），这得到了由主要单倍型构建的邻接树的支持。在37个样本中的27个（73%）发现了单克隆感染，使我们能够识别出15种独特的基因型。
通过18S将大多数马泰勒虫置于一个单系分支中，这表明引入美国的来源有限。当应用于更广泛的全球样本横截面时，这些分子工具应能改善马泰勒虫疫情的来源追踪，并可能有助于防止这种蜱传播寄生虫的传播。
