| Background and objectiveAstrovirus is a kind of non-enveloped single positive sense RNA virus,initially detected by Appleton and Higgins in fecal sample of a child with diarrhea in 1975.Several studies have confirmed that astrovirus can cause vomit,diarrhea and fever in human beings.Rats and asian musk shrews,which have a similar appearance,are called rat-like animals in daily disease control works in mainland China.Both human and rats can be the host of astrovirus.A novel astrovirus was detected in feces of brown rats during 2007 to 2008 by Hongkong research Chu and his fellows.According to their phylogenetic analysis,this novel astrovirus has a close relationship with a novel human astrovirus.Astrovirus is the kind of virus that possess a high genetic variability and that has the ability to make recombination between different genotypes.That makes it possible for Astrovirus to conduct interspecies transmission.Thus the novel virus detected of rat feces may share a common ancestor with the novel human astrovirus.The aims of this study were understand the prevalence of astroviruses in feces of rats and musk shew(Suncus murinus)in Guangdong and Fujian province.After the detection,genetic analysis will be taken to realize the classification information of the viruses and evaluate the risk of an interspecies transmission event.Methods1.Detection of Astroviruses1.1.Sample collectionCages were used to capture rats and musk shrews between Octorber 2014 and February 2016 in Guangzhou and Xiamen province.Total RNAs extracted from feces collected from captured animals was used for viral nucleic acid detection.1.2.Screening test for viral nucleotideA semi-nested PCR method was used to detect viral nucleic acid.Positive rates were calculated separately for different animals.1.3.Confirmation of viral nucleotideBased on available nucleic acid of brown rat astrovirus,viral ORF2 gene specified nested-PCR methods were designed to confirmed genomic type of each positive sample.2.Genome sequencing and genetic analysis2.1.Sample selection and sequencingSome positive samples confirmed by ORF2 gene specified nested-PCR methods were selected for RNA extraction using Tizol.These RNA samples were then sent to Takara Corp.for viral genome sequencing.2.2.Genetic analysisViral sequences obtained in this study were compared to sequencing templates to realize nucleic mutation and amino acid mutation.Mutiple-sequence alignments and phylogenetic analysis was conducted then to evaluate the distance between sequences.Results1.Sample collectionA total of 713 fecal samples from 5 species of rats and Asian musk shrew were included in this study,which 317 from Rattus norvegicus,64 from Rattus losea,44 from Rattus tanezumi,1 from Bandicota indica,1 from Niviventer,and 286 from Suncus murinus.2.Detction of astrovirusA total of 204 samples showed positive results.Rattus losea had the highest positive rate(71.88%),followed by Rattus norvegicus(43.53%),Rattus tanezumi(22.73%),and Suncus murinus(3.5%).Among all positive samples,specified segments were successfully amplified in 93 of positive samples.3.Sequencing and genetic analysisTwo viral genomic sequences were obtained,which one was similar to virus strain detected by Hongkong researcher and the other varies in nucleic acid.Mutiple-sequence alignment and predicted protein structure comparison indicated that brown rat astroviruses might not be able to conduct interspecies transmission between human and rats.Conclusion1.Brown rat astrovirus are detected commonly in rats from some regions in Guangzhou and Xiamen city.2.Asian musk shrews can carry rat astrovirus,but further study should be conducted to confirm the ability for rat astrovirus to infect asian musk shrews.3.More research should be taken to show the varieties of astrovirus.4.Brown rat astrovirus and human astrovirus MLB1 are phylogenetically closely related to each other,so they might share a common ancestor.But rat astroviruses might not be able to conduct interspecies transmission between human and rats. |
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