Infection by the small liver fluke, Opisthorchis viverrini, causes serious public health problems, including cholangiocarcinoma, in Thailand and southeastern Asian countries. Previous studies have reported that O. viverrini represents a species complex with varying levels of genetic differentiation in Thailand and Lao PDR. In this study, we re-examined population genetic structure and genetic diversity of O. viverrini using extensive samples of the parasite collected over 15 years from 12 geographical localities in Thailand and eight localities in Lao PDR. Parasite life-cycle stages of 721 individuals of O. viverrini (91 cercariae, 230 metacercariae and 400 adult worms) were genotyped using 12 microsatellite loci. Metacercariae exhibited genetic diversity comparable with that of experimentally raised adults: metacercariae can therefore be used to represent O. viverrini populations without the need for laboratory definitive hosts. Data obtained from larval as well as adult worms identified two distinct genetic clusters of O. viverrini. Sequences of a portion of the mitochondrial cox1 gene strongly supported the existence of these two clusters. One, the widespread cluster, was found at all sampled sites. The second cluster occurred only in Phang Khon District, Sakon Nakhon Province (SPk), within the Songkram River wetland in Thailand. A striking feature of our data relates to the temporal dynamics of the SPk cluster, which was largely replaced by representatives of the widespread cluster over time. If the SPk cluster is excluded, no marked genetic differences were seen among O. viverrini populations from Thailand and Lao PDR. The underlying causes of the observed population structure and population dynamics of O. viverrini are not known.

小肝吸虫Opisthorchis viverrini 的感染在泰国和东南亚国家引起严重的公共卫生问题，包括胆管癌。先前的研究报告称，O. viverrini代表了泰国和老挝人民民主共和国具有不同遗传分化水平的物种复合体。在这项研究中，我们使用 15 年来从泰国 12 个地理地点和老挝人民民主共和国 8 个地点收集的大量寄生虫样本重新检查了O. viverrini 的种群遗传结构和遗传多样性。721 只O. viverrini个体的寄生虫生命周期阶段使用 12 个微卫星位点对（91 条尾蚴、230 条尾蚴和 400 条成虫）进行基因分型。囊蚴表现出与实验饲养的成虫相当的遗传多样性：因此，囊蚴可用于代表O. viverrini种群，而无需实验室最终宿主。从幼虫和成虫获得的数据确定了O. viverrini 的两个不同的遗传簇。部分线粒体cox1 的序列基因强烈支持这两个簇的存在。一是广泛分布的集群，在所有采样点都被发现。第二个集群仅发生在泰国宋干河湿地内的沙功府 (SPk) 的攀孔县。我们数据的一个显着特征与 SPk 集群的时间动态有关，随着时间的推移，它在很大程度上被广泛集群的代表所取代。如果排除 SPk 集群，泰国和老挝人民民主共和国的O. viverrini种群之间没有发现明显的遗传差异。观察到的O. viverrini种群结构和种群动态的根本原因尚不清楚。