| Avian reovirus(ARV)infections can cause a variety of diseases,including common viral arthritis/tenosynovitis,stunting syndrome and malabsorption syndrome,and characterised mostly with arthritis/tenosynovitis.In recent years,the infection rate of ARVs is increasing,the clinical features of the disease are various,and the epidemic trend is becoming more serious,which lead to much more difficult to prevent and control of ARVs,causing considerable economic losses in poultry husbandry.Only several ARVs were isolated in China and the study on its biological characteristics,evolution,and pathogenicity were rarely reported.Suspected positive samples collected from 2012 to 2016 in our lab were detected and analysed.Data showed that the epidemic trend became more serious and the scope expanded.Two provinces were detected positive in 2012,while the number of positive provinces soared to eight in 2016.The positive infection rate of ARVs increased from 5% in 2012 to 52% in 2015,among which samples from Hei Longjiang?Ji Lin and Liao Ning occupied the biggest amount.The analysis showed that ARVs were prevalent in chicken flocks in various regions of our country and showed increasing infection rate and more serious epidemic trend.In this study,9 ARV field strains,named LN01,LN02,LN03,LN04,LN05,LN06,XY01,WZ01,MS01,were isolated and identified from above positive samples.Biological characteristics analysis showed that the replication ability of all the newly isolates were comparable with S1133 strain in vitro.All strains had high chick embryo mortality,and all chick embryos were detected died within 144 h after infection.Phylogenetic analysis of the ARV ?C gene demonstrated that the newly isolates clustered in lineage 1 and 3.LN05 and JS01 were more closely related to strain 138 in lineage 3.Other isolates were closely related to S1133 strain,and clustered in lineage 3.From the results of the comparative analysis of the amino acid sequences of ?C,10 conservative amino acid mutations were found special in?C amino acid sequence of ARV isolates compared to S1133 strain.Five isolates(HeB02,LN01,MS01,LN05 and JS01)were selected to infect specific-pathogen-free(SPF)chickens,using S1133 strain as a reference.Data showed that all of the infected chickens appeared clinical signs in different degrees 72 h.p.i..The mortality of the newly isolates was all above60%,among which MS01 was 100%,significantly higher than that of S1133 strain(p < 0.05).The results showed that the pathogenicity of ARV isolates was higher than that of the reference strain,and the pathogenicity of the isolates was different in different regions and different isolated times.The viral loads of MS01 in the joints of dead chickens in different time points was significantly higher than that of S1133 strain(p < 0.05),which was consistent with the pathogenicity of SPF chicken,indicating that there is a positive correlation between ARV viral replication ability and its pathogenicity.The replication ability of HeB02 and JS01 were comparable to S1133 strain,while their pathogenicity was higher than that of S1133 strain,indicating that the ability of viral replication in vivo is not the only factor to determine its pathogenicity.To further explore the molecular basis of the high pathogenicity ofMS01,the whole genome sequence was analyzed and showed that the nucleotide sequence homology was above 99% among MS01,S1133,JS01 and HeB02,indicating that single mutation in gene segment may influence viral virlence,but further study need to be carried out to determine the specific sites.In this study,the epidemiology of ARVs in different areas was statistically analyzed,and nine isolates were isolated and identified.The comparative study on the biological characteristics and pathogenicity of the isolates in 2011 and in 2015 was conducted,and the whole gene sequence of MS01 was analyzed,which enriched the database and bioinformatics of ARVs in China,and provided the theoretical and practical basis for the investigation and prevention and control of ARVs in China. |
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