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.

小巴贝斯虫是人类巴贝斯虫病的主要病原体，是一种由至少四个分类群组成的物种复合体（美国，科比、慕尼黑和霍别）。为了进一步评估微进化历史和分类群内的遗传变异性，我们使用了一组6内含子的CCT 7基因作为快速进化的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，欧亚大陆西部至中部和欧亚大陆东北部。科比分类群仅在日本的少数地理疫源地中出现，可进一步细分为两个亚群。慕尼黑和Hobetsu分类群，共同的欧洲和日本，分别表现出很少或没有成对的序列差异之间的地理多样性的样品，这表明在最近的历史中的一个极端的人口瓶颈。我们进一步在北海道岛的根室和淡路岛的洲本进行了实地调查，在水库中，两个谱系以相似的频率共存。对rDNA阳性样品进行谱系特异性PCR检测，结果表明I. ovatus和我persulcatus进行，分别Hobetsu和美国的寄生虫。没有发现携带蜱虫的神户寄生蜂。这一结果表明，第一次，Hobetsu和美国寄生虫是由不同的Ixodid物种。

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.