Investigation On Molecular Epidemiology Of Porcine Reproductive And Respiratory Syndrome Virus In Hebei In 2007-2011

Porcine reproductive and respiratory syndrome is caused by porcine reproductive and respiratory syndrome virus (PRRSV), which caused some clinical features such as fever, abortion, the high mortality rate of piglets before and after weaning, and respiratory disorders of different ages for pigs. It can cause immune suppression, secondary infections,other diseases of the immune failures and so on. PRRS as a major epidemic is now widespread in many countries, and has become the hot issue of global veterinary concerned. It is growing that regarding this disease of occurring, prevalence and reporting, and it has researched from the first report of our country in 1996. Easily mutation characteristics of PRRSV Nsp2 and ORF5 gene leaded to the virus changes of some biological characteristics, which increased difficulty for controlling. Therefore, grasping the variation trend of the prevalence of PRRSV disease is very meaningful to prevent and control it.In the whole PRRSV genome, the variation of non-structural proteins of Nsp2 and structural proteins of ORF5 was largest, which is the target genes of molecular epidemiology and genetic variation analysis of PRRSV. Therefore, exploring the variation of Nsp2, ORF5 genes possesses important significance for PRRSV.In the present study, the clinical samples was collected from different farms of Hebei regions in 2007-2011, and select the lungs, spleen, lymph nodes and other tissue and serum for the material, which were used for the amplication of Nsp2 and ORF5 gene by RT-PCR. Their amplification products were cloned and sequenced in order to analyze the variation of recently prevalent PRRSV.16 Nsp2 gene and 16 ORF5 gene were finally obtained by RT-PCR.The sequence analysis revealed that these Nsp2 gene sequences shared 94.4%～99.8% necleotide and 88.3%～99.4% amino acid identities to each other,73%～74.8% nucleotide and 62.3%～68.5% amino acid identities with VR2332. Compared with some Chinese isolates previously in 2005, BJ-4,CH-1a,HB-1 and HB-2, the obtained Nsp2 gene sequences were closely related to that of HB-1, which is 87.7%～93.2%.The nucleotide and amino acid homology of the obtained fragments ranged from 97%～99.8% and 95%～99.5% for ORF5 gene. When compared with VR2332and LV, the nucleotide varied from 87.1%～88.6% and 55.2%～57.7%, and amino acid identity varied from 87.9%～89.1% and 62.5%～63.8% in ORF5. It was obvious that all isolates sequenced in the research are clustered within North American genotype, while Nsp2 and ORF5 gene showed high degree of diversity.The phylogenetic trees based on the deduced amino acid sequences of Nsp2 and ORF5 gene from this survey and GenBank were constructed. The phylogenetic analysis of Nsp2, combined with the derived information from ORF5 gene indicated that Chinese prevalent PRRSV strains could be divived into 3 subgroups whose representives were BJ-4, CH-1a and HB-1 strain respectively, moreover it was implied that PRRSV strains prevalent in our province entirely belong to the same subgroupⅢ, and was closely relative to HB-1 strain isolated from2002.