Laboratory of Veterinary Parasitology, Joint Faculty of Veterinary Medicine, Yamaguchi University, Yamaguchi, Japan.
Immunobiology Program/Department of Bacteriology and Immunology, Faculty of Medicine, University of Helsinki, Finland.
Int J Parasitol. 2017 Dec;47(14):971-979. doi: 10.1016/j.ijpara.2017.07.001. Epub 2017 Aug 7.
The specific status of Echinococcus canadensis has long been controversial, mainly because it consists of the mitochondrial lineages G6, G7, G8 and G10 with different host affinity: G6 (camel strain) and G7 (pig strain) with domestic cycles and G8 (cervid strain) and G10 (Fennoscandian cervid strain) with sylvatic or semi-domestic cycles. There is an argument whether the mitochondrial lineages should be recognised as separate species which correspond to the biological or epidemiological aggregation. In the present study, the specific status of E. canadensis was investigated using mitochondrial DNA and single copy nuclear DNA markers. Nucleotide sequences of complete mitochondrial cytochrome c oxidase subunit 1 (cox1) and partial nuclear phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold) were determined for 48 isolates of E. canadensis collected from different hosts in a wide range of regions. The mitochondrial phylogeny of cox1 showed that all the isolates were clearly divided into three clades corresponding to G6/G7, G8 and G10. Five and three alleles were confirmed at pepck and pold loci, respectively. These alleles were generally divided into two groups corresponding to G6/G7 or G8 and G10. However, allele sharing was confirmed among individuals belonging to different lineages. The allele sharing occurred primarily in regions where different mitochondrial DNA lineages were found in sympatry. The resultant nuclear mitochondrial discordance suggests the genetic exchangeability among E. canadensis isolates belonging to different lineages. An apparently mosaic parasite fauna that reflects faunal mixing due to natural and anthropogenic disturbance, including introductions and invasion, precludes us from designating each of G6/G7, G8 and G10 into a different species.
细粒棘球绦虫的具体状况长期以来一直存在争议，主要是因为它由具有不同宿主亲和力的线粒体谱系 G6、G7、G8 和 G10 组成：G6（骆驼株）和 G7（猪株）具有国内循环，G8（鹿株）和 G10（芬诺斯堪的亚鹿株）具有森林或半国内循环。关于线粒体谱系是否应被视为对应于生物学或流行病学聚集的单独物种存在争议。在本研究中，使用线粒体 DNA 和单拷贝核 DNA 标记物研究了细粒棘球绦虫的具体状况。为来自不同宿主和广泛区域的 48 个细粒棘球绦虫分离株确定了完整线粒体细胞色素 c 氧化酶亚基 1（cox1）和部分核磷酸烯醇丙酮酸羧激酶（pepck）和 DNA 聚合酶 delta（pold）的核苷酸序列。cox1 的线粒体系统发育表明，所有分离株均明显分为对应于 G6/G7、G8 和 G10 的三个分支。在 pepck 和 pold 基因座分别证实了 5 和 3 个等位基因。这些等位基因通常分为对应于 G6/G7 或 G8 和 G10 的两组。然而，在属于不同谱系的个体之间证实了等位基因共享。等位基因共享主要发生在不同线粒体 DNA 谱系共存的区域。核线粒体不和谐表明属于不同谱系的细粒棘球绦虫分离株之间具有遗传可交换性。明显的嵌合体寄生虫群反映了由于自然和人为干扰（包括引入和入侵）导致的动物群混合，使我们无法将 G6/G7、G8 和 G10 中的每一个指定为不同的物种。
