Abstract
In China, the nematode Trichinella spiralis is the main aetiological agent of human trichinellosis. We performed multi-locus microsatellite typing of T. spiralis isolates to improve the current knowledge of the evolution and population diversity. First, seven polymorphic microsatellite loci were used to infer the genetic diversity of T. spiralis collected in 10 endemic regions. Then, a Bayesian model-based STRUCTURE analysis, a clustering based on the neighbor-joining method, and a principal coordinate analysis (PCA) were performed to identify the genetic structure. Finally, the phylogenetic position of Chinese isolates was explored based on six mitochondrial and nuclear genetic markers (cox1, cytb, 5S ISR, ESV, ITS1, and 18S rDNA) using the maximum likelihood and Bayesian methods. In addition, the divergence time was estimated with multiple genes using an uncorrelated log-normal relaxed molecular-clock model. A total of 16 alleles were detected in 2,310 individuals (1,650 muscle larvae and 660 adult worms) using seven loci. The STRUCTURE analysis indicated that the T. spiralis isolates could be organized and derived from the admixture of two ancestral clusters, which was also substantiated through the clustering analysis based on the allelic data. PCA separated most samples from Tiandong, Guangxi (GX-td), and Linzhi, Tibet (Tibet-lz), from the remaining isolates. However, both maximum likelihood and Bayesian inference supported the close relationship between Xiangfan, Hubei (HB-xf), and GX-td. The molecular dating analysis suggested that the Chinese isolates started to diverge during the Late Pleistocene (0.69 Mya). Generally, T. spiralis was observed to harbor low genetic variation, and further investigation with deeper sampling is needed to elucidate the population structure.
Highlights
Nematodes of the genus Trichinella are cosmopolitan zoonotic parasites, and more than 100 species of mammals, birds, and reptiles have been confirmed as suitable hosts (Pozio, 2014)
11 T. spiralis isolates were originally collected from naturally infected hosts in 10 geographical locations in China
We prepared 3,850 individuals originating from 10 geographic regions representing 10 T. spiralis isolates and performed a genetic variation analysis of these samples using seven microsatellite loci to investigate the genetic structure
Summary
Nematodes of the genus Trichinella are cosmopolitan zoonotic parasites, and more than 100 species of mammals, birds, and reptiles have been confirmed as suitable hosts (Pozio, 2014). In China, human cases have been recorded in 17 out of the 34 provinces/autonomous regions/municipalities (Cui et al, 2011). Great achievements have been made in the taxonomy, phylogeny, and biogeography of the Trichinella genus during the last decade (Zarlenga et al, 2006; Pozio et al, 2009; Mohandas et al, 2014; Korhonen et al, 2016), only a few studies have focused on the genetic diversity of the Chinese T. spiralis population. Human trichinellosis cases have been recorded in 17 provinces/autonomous regions/municipalities of China; only seven geographical isolates from the endemic regions were identified (Yang et al, 2008; Fu et al, 2009; Wang et al, 2012; Zhang et al, 2016). Our knowledge of the population diversity of T. spiralis obtained from different geographical areas of China is still fragmented
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