Abstract
BackgroundCystic echinococcosis (CE) in humans and livestock is caused by Echinococcus granulosus (sensu lato). In China where CE is endemic, a number of studies have shown that Echinococcus granulosus (sensu stricto) is majorly responsible for CE. However, E. canadensis (G6) which is the second leading cause of CE is now being detected in most parts of the country. In this study, the species diversity and genetic variation of Echinococcus granulosus (s.l.) in four counties in Tibet Autonomous Region of China were investigated.MethodsInfection with Echinococcus granulosus (s.s.) in yaks and sheep was identified using NADH dehydrogenase subunit 1 and 5 (nad1 and nad5) mitochondrial genes while the genotype G6 of E. canadensis initially diagnosed with NADH dehydrogenase subunit 1 (nad1) was further confirmed by analysis of the complete mitochondrial genome and a phylogenetic network constructed based on the nad2 and nad5 genes.ResultsOut of 85 hydatid cyst samples collected from slaughtered sheep (n = 54) and yaks (n = 31), 83 were identified as E. granulosus (s.s.) G1 (n = 77), G3 (n = 6) and 2 were identified as E. canadensis G6. Analysis of the nad1/nad5 genes revealed 16/17 mutations with 9/14 parsimony informative sites resulting in 15/14 haplotypes, respectively. Haplotype diversity (Hd) and nucleotide diversity (π) of E. granulosus (s.s.) population were 0.650 and 0.00127 for nad1 and 0.782 and 0.00306 for nad5, respectively, with an overall negative Tajima’s D and Fu’s Fs. A low FST indicated no genetic difference between isolates from sheep and yaks.ConclusionPockets of infection with E. canadensis (G6, G7, G8 and G10) have been previously reported in sheep, goats, yaks and/or humans in different parts of China. While the G6 genotype has been previously reported in sheep in the Tibet Autonomous Region, the detection in a yak in the present study represents the first to the best of our knowledge. Therefore, we recommend future surveys and control efforts to comprehensively investigate other potential intermediate hosts for the prevalence and genetic diversity of the E. canadensis group (G6, G7, G8 and G10) across the country and their inclusion into the existing CE control programme.
Highlights
Cystic echinococcosis (CE) in humans and livestock is caused by Echinococcus granulosus
Cystic echinococcosis (CE) is a parasitic zoonosis caused by tapeworm species of Echinococcus granulosus (s.l.), which infect humans and livestock upon ingestion of the infective egg stage from the definitive host resulting in the development of hydatid cyst of the metacestode larval stages in the liver, lungs and sometimes in other organs
Haplotype networks of Echinococcus granulosus (s.s.) Of the 83 E. granulosus (s.s.) isolates, 15 haplotypes resulted from the analysis of nad1 gene sequences (Fig. 2a, Table 2) and 14 from nad5 gene (Fig. 2b, Table 2)
Summary
Cystic echinococcosis (CE) in humans and livestock is caused by Echinococcus granulosus (sensu lato). The species diversity and genetic variation of Echinococcus granulosus (s.l.) in four counties in Tibet Autonomous Region of China were investigated. Recent reports of the G6 genotype and other members of E. canadensis group in areas other than Xinjiang Uygur Autonomous Region, are raising concerns on its host range and public health significance [12, 14, 15, 18]. The species diversity and genetic variation of Echinococcus species in four counties in the Tibet Autonomous Region of China were investigated and for the first time, the presence of E. canadensis (G6) in yak was confirmed using mitochondrial DNA markers (nad and nad5) and the complete mitochondrial genome analysis
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