Macnish M G, Morgan-Ryan U M, Monis P T, Behnke J M, Thompson R C A
WHO Collaborating Centre for the Molecular Epidemiology of Parasitic Infections, Division of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, Western Australia, Australia 6150.
Parasitology. 2002 Dec;125(Pt 6):567-75. doi: 10.1017/s0031182002002366.
Since isolates of Hymenolepis nana infecting humans and rodents are morphologically indistinguishable, the only way they can be reliably identified is by comparing the parasite in each host using molecular tools. In the current study, isolates of H. nana from rodent and human hosts from a broad geographical range were sequenced at the ribosomal first internal transcribed spacer (ITS1), the mitochondrial cytochrome c oxidase subunit 1 (C01) gene and the nuclear paramyosin gene loci. Twenty-three isolates of H. nana were sequenced at the ITS1 locus and this confirmed the existence of spacers which, although similar in length (approximately 646 bp), differed in their primary sequences which led to the separation of the isolates into 2 clusters when analysed phylogenetically. This sequence variation was not, however, related to the host of origin of the isolate, thus was not a marker of genetic distinction between H. nana from rodents and humans. Sequencing of a 444 bp fragment of the mitochondrial cytochrome c oxidase 1 gene (C01) in 9 isolates of H. nana from rodents and 6 from humans identified a phylogenetically supported genetic divergence of approximately 5% between some mouse and human isolates. This suggests that H. nana is a species complex, or 'cryptic' species (=morphologically identical yet genetically distinct). A small segment of the nuclear gene, paramyosin, (625 bp or 840 bp) was sequenced in 4 mouse and 3 human isolates of H. nana. However, this gene did not provide the level of heterogeneity required to distinguish between isolates from rodent and human hosts. From the results obtained from faster evolving genes, and the epidemiological evidence, we believe that the life-cycle of H. nana that exists in the north-west of Western Australia is likely to involve mainly 'human to human' transmission.
由于感染人类和啮齿动物的微小膜壳绦虫分离株在形态上无法区分，唯一能够可靠鉴定它们的方法是使用分子工具比较每个宿主中的寄生虫。在本研究中，对来自广泛地理区域的啮齿动物和人类宿主的微小膜壳绦虫分离株进行了核糖体第一内部转录间隔区（ITS1）、线粒体细胞色素c氧化酶亚基1（C01）基因和核副肌球蛋白基因位点的测序。对23个微小膜壳绦虫分离株的ITS1位点进行了测序，这证实了间隔区的存在，尽管其长度相似（约646 bp），但其一级序列不同，在系统发育分析时导致分离株分为2个簇。然而，这种序列变异与分离株的宿主来源无关，因此不是啮齿动物和人类微小膜壳绦虫之间遗传差异的标记。对9个来自啮齿动物和6个来自人类的微小膜壳绦虫分离株的线粒体细胞色素c氧化酶1基因（C01）的444 bp片段进行测序，确定了一些小鼠和人类分离株之间在系统发育上支持的约5%的遗传差异。这表明微小膜壳绦虫是一个物种复合体或“隐存”物种（=形态相同但遗传上不同）。对4个小鼠和3个人类微小膜壳绦虫分离株的核基因副肌球蛋白的一小段（625 bp或840 bp）进行了测序。然而，该基因并未提供区分啮齿动物和人类宿主分离株所需的异质性水平。根据从进化较快的基因获得的结果以及流行病学证据，我们认为西澳大利亚州西北部存在的微小膜壳绦虫的生命周期可能主要涉及“人传人”传播。
