Abstract
BackgroundCervids used to be considered the only animal intermediate hosts of the G10 genotype of Echinococcus canadensis. Yaks are often herded in the Qinghai-Tibet Plateau, China, where echinococcosis remains prevalent. However, no E. canadensis G10 cases have been recorded in yaks until now. The aim of our study was to identify causative agents of echinococcosis in yaks in this region.MethodsTotal genomic DNA was extracted from the germinal layer of one hydatid using a Blood and Tissue Kit. Full-length mitochondrial (mt) cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) genes were amplified by PCR. All purified PCR products were directly sequenced in both directions. Then seven pairs of overlap primers were designed to amplify the entire mt genome sequence of a suspected E. canadensis G10 isolate. Phylogenetic analyses were performed based on concatenated nucleotides from the 12 protein-coding genes of mt genomes of Echinococcus species in a Bayesian framework using MrBayes v3.1 and implementing the GTR + I + G model.ResultsHydatids were found in yaks (n = 129) when organs were inspected at the slaughterhouse in Maqu county, Gannan Tibetan Autonomous Prefecture, Gansu Province, China in October 2016. Of these, 33 (25.6%) harbored up to a dozen hydatid cysts. One cyst from each yak was characterized by sequencing its mitochondrial (mt) cox1 and nad1 genes. On the basis of these sequence data, 32 cysts were identified as Echinococcus granulosus (sensu stricto) (G1-G3) and the remaining one was identified as the G10 genotype of E. canadensis. Its mt genome was then fully sequenced and compared with that of the G10 genotype in GenBank (AB745463). Phylogenetic analysis using complete mt genomes confirmed the Chinese cyst as belonging to the G10 genotype.ConclusionsTo our knowledge, this is the first report globally of E. canadensis (G10) from yaks in China, which suggests that the G10 genotype has a wider geographical distribution and broader host range than previously believed. This genotype has therefore potential risks to human health and animal husbandry.
Highlights
Cervids used to be considered the only animal intermediate hosts of the G10 genotype of Echinococcus canadensis
Recent phylogenetic studies based on both mitochondrial and nuclear Deoxyribonucleic acid (DNA) genes show that E. granulosus (s.l.) is comprised of at least five independent species: E. granulosus (s.s.), E. equinus (G4), E. ortleppi (G5), E. canadensis (G6-G10) and E. felidis [3,4,5,6]
These E. canadensis genotypes closely match the intermediate host-associated strains described in the earlier reports where E. canadensis G10 was named as cervid strain [11], which was first found in cervids in northeastern Finland representing a distinct genotype [12]
Summary
Cervids used to be considered the only animal intermediate hosts of the G10 genotype of Echinococcus canadensis. Cystic echinococcosis (CE) is one of the most important parasitic diseases in humans and one of the 17 neglected diseases (NTDs) prioritized by the World Health Organisation (WHO) in 2012 It is a widespread zoonosis caused by the cyst stage of Echinococcus granulosus (sensu lato) [1, 2]. Molecular and morphological studies suggest that it would be better if these E. granulosus (G6-G10) be re-classified as a separate species (i.e. E_canadensis) [5, 7,8,9,10] These E. canadensis genotypes closely match the intermediate host-associated strains described in the earlier reports where E. canadensis G10 was named as cervid strain [11], which was first found in cervids in northeastern Finland representing a distinct genotype [12]. A human case of the G10 type was recently reported in China [2]
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