2016-2017年江西地区猪繁殖与呼吸综合征病毒分子流行病学调查及ORF5基因变异分析

为了解近年来江西地区猪繁殖与呼吸综合征病毒（porcine reproductive and respiratory syndrome virus，PRRSV）分子流行病学和其遗传变异情况，本次调查于2016-2017年从江西省各地区规模化猪场采集453份疑似猪繁殖与呼吸综合征（PRRS）的病料，采用RT-PCR方法对所有病料进行检测。结果发现，其中321份病料为PRRSV阳性，阳性率为70.86%，各地区的阳性率在19.15%~84.85%之间。挑选14份阳性样品测序后，经ORF5基因序列分析，江西地区各PRRSV毒株ORF5基因的核苷酸同源性为83%~100%，PRRSV流行毒株与参考毒株的同源性在59.9%~98.5%之间。基于ORF5基因的进化树分析表明，14个测序毒株均为美洲型毒株，其中有4株为基因亚型Ⅰ，即高致病性毒株（HP-PRRSV）；3株为基因亚型Ⅱ，即经典毒株；3株为基因亚型Ⅲ，即NADC30-like毒株；4株为新出现的基因亚型Ⅳ。氨基酸序列比对分析表明，基因亚型Ⅰ、Ⅱ、Ⅲ和Ⅳ毒株ORF5基因编码的GP5蛋白氨基酸在3个表位及2个重要的抗原相关区域存在较大变异，其中以NADC30毒株为代表的基因亚型Ⅲ毒株和以GD1404毒株为代表的基因亚型Ⅳ毒株均表现出独有的氨基酸变异，这些变异可能会影响GP5蛋白的免疫原性。本次调查结果表明，2016-2017年江西地区PRRSV流行出现了新形势，美洲型毒株出现了多基因亚型共同存在的局面，以高致病性毒株（HP-PRRSV）为主，NADC30-like毒株和新基因亚型等新毒株的比例较高，同时还存在经典毒株；持续实时监测PRRSV的毒株流行和变异情况，可为临床诊断、药物和疫苗开发及PRRS的科学防控提供依据。

Molecular Epidemiology Investigation and ORF5 Gene Variation Analysis of Porcine Reproductive and Respiratory Syndrome Virus in Jiangxi Province During 2016 to 2017

To investigate the genetic variation and molecular epidemiology of porcine reproductive and respiratory syndrome virus (PRRSV) in Jiangxi province in the recent years,a total of 453 tissue samples were collected from porcine reproductive and respiratory syndrome (PRRS) suspected cases in pig farms in different regions of Jiangxi province during 2016 to 2017,and then examined by RT-PCR.Of the 453 clinical samples,321 were identified positive for PRRSV,with a positive rate of 70.86%.The positive rates were varying from 19.15% to 84.85% in different regions.14 positive samples were sequenced,and the nucleotide homologies of ORF5 gene were among 83% to 100% for the strains identified in this study,and 59.9% to 98.5% for reference strains of PRRSV.14 sequenced strains all belonged to North America type (genotype Ⅱ) PRRSV in this study,4 strains belonged to the highly pathogenic PRRSV (HP-PRRSV,subtype Ⅰ),3 strains belonged to the classic PRRSV (subtype Ⅱ),3 strains belonged to NADC30-like PRRSV (subtype Ⅲ),and 4 strains belonged to the new subtype of PRRSV (subtype Ⅳ).Sequence analysis on deduced amino acid of GP5 coded by ORF5 gene indicated that the significant variations were observed in three epitopes and two important antigenic regions in PRRSVs belonged to the four subtypes (subtypesⅠ,Ⅱ,Ⅲ and Ⅳ).Subtype specific variations in subtypes Ⅲ and Ⅳ were also observed in amino acid of GP5,which might lead to the variation of antigenecity of GP5 protein.The results indicated that there was a new situation of PRRSV strains circulating in Jiangxi province during 2016 to 2017,with multi-subtypes of strains existed and co-infected in pigs.And the most popular subtype was HP-PRRSV,while there were high rates of newly emerged NADC30-like strains and new subtype strains;It was necessary to continuously monitor the epidemiology of PRRSV,which would be benefit for the development of new diagnostic methods,drugs and vaccines for the prevention and control of PRRS.