中国部分地区2005-2007年猪繁殖与呼吸综合征病毒分离株ORF5基因和Nsp2基因遗传变异分析

Genetic Variations of ORF5 Gene and Nsp2 Gene of Porcine Reproductive and Respiratory Syndrome Virus Isolates from China in 2005-2007

【目的】为分析2005-2007年间中国部分省区猪繁殖与呼吸综合征病毒(PRRSV)流行毒株的分子生物学特征,了解其遗传演化规律,查明中国目前PRRSV流行毒株现状。【方法】应用病毒分离方法从中国4个省份在2005-2007年间采集的81份疑似蓝耳病病料中分离到36株猪繁殖与呼吸综合征病毒,应用RT-PCR方法对36株PRRSV现地分离株的ORF5基因和Nsp2基因进行扩增和序列分析。【结果】36株现地分离株均属于美洲型PRRSV,ORF5基因全长均为603bp,未发现有基因缺失或插入,编码约200个氨基酸,分离株推导氨基酸序列变异主要发生在9～39位;36个分离株中有15株PRRSVNsp2基因全长为2940bp,21株PRRSVNsp2基因全长为2850bp;发生Nsp2缺失的PRRSV在Nsp2基因第481位、532～560位发生了不连续缺失,共缺失30个氨基酸。与GeneBank中收录的14个PRRSVORF5、Nsp2基因进行核苷酸及氨基酸序列比较和分析,系统进化关系显示,除B02-2005株可能与疫苗株有关外,多数现地分离株与Ch-1a株遗传距离较近,不同年份分离到的毒株与早期PRRSV分离株的同源性逐年降低。【结论】根据氨基酸变异情况对PRRSV现地分离株进行亚群聚类分析,发现36株现地分离株分别归属于以VR-2332为代表的4亚群,以BJ-4为代表的1亚群和以Ch-1a为代表的2亚群。进化关系表明PRRSVORF5、Nsp2基因及其推导的氨基酸序列均发生了较大变异,不同地区PRRSV分离株的遗传关系存在交叉现象,地域特征不明显。

[Objective] PRRSV were isolated from China in 2005-2007 to recognize the molecular biology character, phylogenetic relationship and the state quo of PRRSV prevalent isolates. [Method] 36 PRRSV isolates were isolated from 81 suspected clinical samples in 4 provinces which suffered PRRS in China in 2005-2007, ORF5 and Nsp2 genes of these isolates were sequenced and analyzed. [ Result ] 36 isolates are North America PRRSV, which of ORF5 genes were composed of 603 nucleotides, encoded polypeptides of 200 amino acid residues, no gene deletion or inseration. Variations of the deduced amino acids of ORF5 gene mainly occurred at positions of 9 to 39. Nsp2 genes of PRRSV isolates were composed of 2940 or 2850 nucleotides. Compared with 15 PRRSV isolates, Nsp2 genes deletions of 21 PRRSV isolates were occured at positions of 481 and 532-596 amino acid. Compared with 14 PRRSV ORF5 and Nsp2 genes recorded by GenBank, most isolates show a close distance evolutionary relationship with Ch-la, except for B02-2005, which may respect with PRRS vaccine virus. PRRSV isolates from different times show descendant homology compared with earlier isolates. [ Conclusion ] Based on amino acid sequence phylogenetic tree of ORF5 gene and Nsp2 gene, the 36 PRRSV isolates partly belong to subgroup IV represented by VR-2332, partly to subgroup I represented by BJ-4, and partly to subgroup II represented by Ch-la. PRRSV ORF5, Nsp2 nucleotides and amino acids have taken place a larger variation, the genetic relationship of PRRSV isolates from different regions exist cross-cutting phenomenon, no obvious geographical characteristics.