Study of intra-species diversity in Giardia intestinalig Assessment of a genotype distribution in isolated islands of Indonesia

我们的目的是确定肠贾第鞭毛虫种内遗传多样性的现状以及维持该物种种群多样性的因素。用18S小亚基核糖体RNA、谷氨酸脱氢酶和磷酸丙糖异构酶基因等多位点标记对不同地理位置(印度尼西亚、尼泊尔和日本)的不同哺乳动物(狗、猪、鼠和人)的贾第鞭毛虫样本进行了分析。在人类样本中，A和/或B组合内的各种亚型被清楚地分类，但没有观察到特定部位的基因型分布。我们还证实，在印度尼西亚农村地区的几个人类样本中，存在C和D组合，这两种组合已被确认为狗特有的基因类型。对同一地点采集的人和动物分离株的测定序列的比较明确地证实了B集合群中每个亚集合簇的存在。结合先前关于肠杆菌属寄主专一性的指示，这些结果表明寄主专一性可能是该病原菌遗传多态的集合性水平的部分原因，但每个集合体内的多样性，特别是B集合体的多样性似乎不是这种情况。虽然目前的地理分布和病原菌的分离不被认为是其遗传多样性的驱动力，因为这种分布没有指示任何地点，但我们在这里表明了一个地点的生态位分离可能与多样性的形成有关。生态位分离可能使贾第鞭毛虫积累基因组中独特的突变，并在克隆种群中保持新的多样性。

We aimed to determine the status of intra-species genetic diversity of Giardia intestinalis and the factors that contribute to the maintenance of population diversity in this species. Giardia samples collected from various mammals (dog, pig, mouse and human) i n different geographical sites(Indonesia, Nepal and Japan) were analyzed using multilocus markers (18S small subunit ribosomal RNA, glutamate dehydrogenase and triosephosphate isomerase genes). In the human samples, various sub-genotypes within assemblage A and/or B were clearly classified ; however, no site-specific distribution of genotypes was observed. We also confirmed that assemblages C and D, which have been recognized as dog-specific genotypes, were present in a few human samples in a rural area of Indonesia. A comparison of the determined sequences of human and animal isolates collected at the same site specifically confirmed the presence of each sub-assemblage cluster within assemblage B.Taken together with previous indications of assemblage-level host specificities in G. intestinalis, these results demonstrate that host specificities could be partly responsible for the assemblage levels of genetic polymorphism in this pathogen, however the diversity within each assemblage especially assemblage B seemed not in the case. Although the present geographical distributions and isolations of the pathogen were not thought to be a driving force of its genetic diversity since the distribution did not indicate any locality, we showed here the possibility that niche separations in a site might be related to the diversity formation. Niche separation may enable Giardia to accumulate the unique mutations in the genome and maintain novel diversity within the clonal population.