Intron Sequences in the CCT7 gene Show Diverse Evolutionary Histories of the Four Lineages withinthe "Babesia microti-Group," a Genetically Related Species-Complex Including Pathogens of Humans.

微巴贝斯虫是人类巴贝斯虫病的主要病原，是一个由至少四个分类群（美国、神户、慕尼黑和河北）组成的物种复合体。为了进一步评估该分类群的微进化历史和遗传变异性，我们使用CCT7基因中的6个内含子作为快速进化的DNA标记。系统发育和比较序列分析将美国分类群细分为三个地理亚支——北美、欧亚大陆西部到中部和欧亚大陆东北部。神户分类群在日本仅分布于少数地理区，可进一步划分为两个亚群。欧洲和日本共有的慕尼黑和Hobetsu类群在不同地理位置的样本中表现出很少或没有成对序列差异，表明在最近的历史中存在极端的种群瓶颈。我们进一步在北海道的Nemuro和Awaji岛的Sumoto进行了实地调查，发现储层中有两种谱系以相似的频率共存。对rdna阳性样本进行谱系特异性PCR检测，发现卵形伊蚊和过纵伊蚊分别携带霍别梭和美国寄生虫。未检出携带神户寄生虫的蜱虫。这一结果首次表明，两种寄生蜂是由不同的易蚊种传播的。

Babesia microti, the main causal agent of human babesiosis, is a species-complex comprised of at least four taxa (the U.S., Kobe, Munich and Hobetsu). To further assess micro-evolutionary history and genetic variability within the taxon, we used a set of 6 introns in the CCT7 gene as a rapidly evolving DNA marker. Phylogenetic and comparative sequence analysis subdivided the U.S. taxon into three geographic subclades - North America, western to central Eurasia, and northeastern Eurasia. The Kobe taxon, which occurs only in a few geographic foci in Japan could further be subdivided into two subgroups. The Munich and Hobetsu taxa, common to Europe and Japan, respectively, exhibited little or no pairwise sequence divergence among geographically diverse samples, suggesting an extreme population bottleneck in the recent histories. We further conducted a field investigation at Nemuro on Hokkaidoisland and Sumoto on Awaji island, where up to two lineages co-occur with similar frequency in reservoir. Lineage specific PCR for rDNA-positive samples demonstrated that I. ovatus and I. persulcatus carried, respectively, the Hobetsu and U.S. parasites. No Kobe-parasote carrying tick was detected. This result indicate that, for the first time, Hobetsu and U.S. parasites are vectored by different Ixodid species.