Pathogenic Porcine Reproductive And Respiratory Virus: Molecular Epidemiology: Genetic Variation Of NSP2 And ORF5

PRRS was first recognized in North America in 1980s and spread rapidly throughout the world, the syndrome that caused reproductive and respiratory problems in swine was initially called "mystery swine disease" and is now termed "porcine reproductive and respiratory syndrome (PRRS)". Porcine reproductive and respiratory syndrome (PRRS) poses a significant economic threat to the swine industry worldwide.The etiological agent, PRRSV, Porcine reproductive and respiratory syndrome virus (PRRSV) is reported to have evolved at a higher evolutionary rate than other RNA viruses. Most recently "porcine high fever disease" was reported in China starting in 2006 with highly pathogenic PRRSV(HP-PRRSV) being a critical virus associated with high morbidity and mortality (20%) associated with this syndrome. To better understand the epidemiology of this virus in China, and to examine the evolutionary characteristics of PRRSV in China after the 2006 outbreak,and to explore the possible mechanism of the pathogenicity of the highly pathogenic PRRSV, we started this work.In this research, we investigated the epidemicity and genetic diversity of PRRSV based on the detection of 1060 clinical samples and sequenced of the ORF5 sequences and the partial NSP2 sequences of 101 isolates from 2009 to 2010 in China from epidemic regions in AnHui, HuBei, HeNan, GuangXi, JiangXi, FuJian, GuangDong, HeBei, ShaanXi and etc. province.Our results showed that the positive rate of PRRSV infection 71.71% in 2009 and 54.03% in 2010, and that the highly pathogenic PRRSV was now the dominant strain in China. Through sequence alignment analysis of amino acid residue, it was found that the similarity of NSP2s is 83.6%-100%, of ORF5s is 89.5%-100%. Phylogenetic analyses showed that all these 101 isolates belonged to the North American genotype, and moreover we divided North American genotype into four subgenotypes. Furthermore, a re-emerging strain which apparently evolved from the highly pathogenic PRRSV in 2006 appeared to be widely prevalent in China from 2009 onwards. Sequence analyses revealed that the hypervariable region of NSP2 in most of the isolates contained a discontinuous deletion equivalent to 30 amino acids, along with other types of deletions in individual. Extensive amino acid substitutions in the GP5 sequence translated from ORF5 were found, particularly in the primary neutralization epitope and the potential N-glycosylation sites. Compared with the classical PRRSV, the quantity and position of the potential N-glycosylation sites had changed.Our results suggest that Chinese PRRSV was undergoing the evolution quickly and appear to evolve immune escape potentiality against the current clinically used vaccine. Information from this study will help towards understanding the evolutionary characteristics of Chinese PRRSV and assist ongoing efforts to develop and use PRRSV vaccines in the future.