Phylogenetic analysis and molecular characteristics of seven variant Chinese field isolates of PRRSV

Chengmin Wang,Jing Luo,Bin Wu,Hongxuan He,Yunhai Guo,Hongmei Zhang,Guoying Dong,Said Amer,Baohua Zhao

doi:10.1186/1471-2180-10-146

Abstract

BackgroundPorcine reproductive and respiratory syndrome (PRRS) has now been widely recognized as an economically important disease. The objective of this study was to compare the molecular and biological characteristics of porcine reproductive and respiratory syndrome virus (PRRSV) field isolates in China to those of the modified live virus (MLV) PRRS vaccine and its parent strain (ATCC VR2332).ResultsFive genes (GP2, GP3, GP4, GP5 and NSP2) of seven isolates of PRRSV from China, designated LS-4, HM-1, HQ-5, HQ-6, GC-2, GCH-3 and ST-7/2008, were sequenced and analyzed. Phylogenetic analyses based on the nucleotide sequence of the ORF2-5 and NSP2 showed that the seven Chinese isolates belonged to the same genetic subgroup and were related to the North American PRRSV genotype. Comparative analysis with the relevant sequences of another Chinese isolate (BJ-4) and North American (VR2332 and MLV) viruses revealed that these isolates have 80.8-92.9% homology with VR-2332, and 81.3-98.8% identity with MLV and 80.7-92.9% with BJ-4. All Nsp2 nonstructural protein of these seven isolates exhibited variations (a 29 amino acids deletion) in comparison with other North American PRRSV isolates. Therefore, these isolates were novel strain with unique amino acid composition. However, they all share more than 97% identity with other highly pathogenic Chinese PRRSV strains. Additionally, there are extensive amino acid (aa) mutations in the GP5 protein and the Nsp2 protein when compared with the previous isolates.ConclusionsThese results might be useful to study the genetic diversity of PRRSV in China and to track the infection sources as well as for vaccines development.

Highlights

Porcine reproductive and respiratory syndrome (PRRS) has been widely recognized as an economically important disease
Two subgroups were classified based on ORF2, ORF3, ORF4, ORF5 and NSP2 genes of Chinese American genotype isolates, and named as subgroup AM-I and AM-II (Figure 1)
These seven isolates clustered to the subgroup AM-I for ORF2-5 and NSP2, whereas the Chinese isolates BJ-4, VR2332 and modified live virus (MLV) were affiliated with subgroup AM-II based on ORF2-4 and NSP2

Summary

Introduction

Porcine reproductive and respiratory syndrome (PRRS) has been widely recognized as an economically important disease. Porcine reproductive and respiratory syndrome virus (PRRSV) is recognized as one of the major infective agents in the pig industry worldwide since its appearance in the 1980s. It was first diagnosed in the USA in 1987 [1], immediately found in Europe, soon disseminated to the rest of the world [2]. Based on phylogenetic analyses of PRRSV is a small, enveloped, single positive-stranded RNA virus including a genome of about 15 kb, encoding nine ORFs [2,7,8]. The presence of genetically divergent viruses in a swine population may complicate the disease control by vaccination, because the PRRSV vaccine efficacy is reduced when the challenge virus is a virus of a different genotype [17] or of a different phylogenetic cluster within the same genotype [18]

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Conclusion