Dusitsittipon Sirilak, Criscione Charles D, Morand Serge, Komalamisra Chalit, Thaenkham Urusa
Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
Department of Biology, Texas A&M University, TX, USA.
Mol Phylogenet Evol. 2017 Feb;107:404-414. doi: 10.1016/j.ympev.2016.12.002. Epub 2016 Dec 8.
Delimitation of species is still a necessity among parasitic pathogens especially where morphological characters provide limited discernibility. Identification of cryptic lineages (independently evolving lineages that are morphologically similar) is critical as there could be lineage-specific traits that are of epidemiological importance. Angiostrongylus cantonensis is a zoonotic pathogen that can cause eosinophilic meningitis in humans. Recent reports of single marker sequence divergence hint at the potential for cryptic diversity in this lungworm. However, to definitively address if single marker divergence corresponds to independent evolving lineages, a multilocus approach is necessary. Using multilocus data, our goal was to determine if there were cryptic lineages within Thailand, a country plagued by several outbreaks and isolated cases of A. cantonensis infection. We analyzed the genetic structure of A. cantonensis samples collected from snails, Achatina fulica, across provinces in Thailand. Multilocus data (mitochondrial sequence data and 12 nuclear microsatellites) and individual based analyses were used to test for cryptic lineages. We found strong linkage disequilibrium patterns between mitochondrial haplotypes and nuclear-identified genetic clusters. There were clearly two divergent and independent clades. Moreover, within each clade, the data suggested additional substructure where individual provinces were likely to harbor unique genetic clusters. The results indicate there are at minimum two and possibly up to eight cryptic lineages within the assumed single species of A. cantonensis. Importantly, the two main clades do not show geographic affiliation and can be found in sympatry. With recent studies highlighting A. cantonensis strain diversity in pathogenicity and infectivity, it will be important to determine if these critical epidemiological traits are associated with specific lineages.
在寄生性病原体中，物种划分仍然是必要的，尤其是在形态特征提供的辨别能力有限的情况下。识别隐秘谱系（形态相似但独立进化的谱系）至关重要，因为可能存在具有流行病学重要性的谱系特异性特征。广州管圆线虫是一种人畜共患病原体，可导致人类嗜酸性粒细胞性脑膜炎。最近关于单标记序列分歧的报道暗示了这种肺线虫存在隐秘多样性的可能性。然而，要确定单标记分歧是否对应于独立进化的谱系，就需要采用多基因座方法。利用多基因座数据，我们的目标是确定在泰国这个饱受广州管圆线虫感染多次暴发和散发病例困扰的国家内是否存在隐秘谱系。我们分析了从泰国各省的褐云玛瑙螺中采集的广州管圆线虫样本的遗传结构。使用多基因座数据（线粒体序列数据和12个核微卫星）以及基于个体的分析来检测隐秘谱系。我们发现线粒体单倍型与核鉴定的遗传簇之间存在强烈的连锁不平衡模式。明显有两个不同且独立的分支。此外，在每个分支内，数据表明存在额外的亚结构，其中各个省份可能拥有独特的遗传簇。结果表明，在假定的单一物种广州管圆线虫中至少存在两个，可能多达八个隐秘谱系。重要的是，这两个主要分支没有地理归属关系，并且可以在同域中发现。鉴于最近的研究强调了广州管圆线虫菌株在致病性和感染性方面的多样性，确定这些关键的流行病学特征是否与特定谱系相关将非常重要。
