Biological Characteristics And Control Study On Porcine Reproductive And Respiratory Syndrome Virus JS2014 Strain

Porcine reproductive and respiratory syndrome(PRRS)was first reported in the United States in 1987,PRRSV has already been one of the most economically important diseases of the global swine industry.It caused by porcine reproductive and respiratory syndrome virus(PRRSV),is a serious infectious disease of swine.PRRSV was firstly described in China in 1995,along with the development of China's pig industry,PRRS annually on China's pig industry has brought huge losses,and the amount cannot be estimated.Especially the 2006 outbreak of HP-PRRS and the 2013 outbreak of NADC30-like on China's pig industry are causing huge economic losses.In order to study the prevalence of Porcine Reproductive and Respiratory Syndrome Virus(PRRSV)in Southern China,this study tested 1038 serum samples and 1816 disease samples(lung,brain,lymph nodes)of 51 pig farms in different regions of South China during 2015-2017.The results showed that 512 of the 1038 collected swine sera were PRRSV positive with the positive rate of about 49.3%.Among the 2854 collected samples,134 samples were detected as classical PRRSV,the positive detection rate was 4.7%;1151 samples were detected as highly pathogenic PRRSV,the positive detection rate was 40.3%;605 samples were detected as the NADC30-like strain,the positive detection rate was 21.2%.There was PRRSV mixed infection in the samples.The detection rate of co-infection of classic PRRSV + HP-PRRSV was 2.5%.The rate of co-infection of classic PRRSV + NADC30-like PRRSV was 2.0%,and the rate of co-infection of HP-PRRSV + NADC30-like PRRSV was 13.1%.In order to further study the genetic variation of PRRSV in Southern China,the ORF5 gene of PRRSV positive samples was amplified and sequenced.According to the sequence alignment,the PRRSV strains in South China showed diversity,and the sequences belonged to Linage 8,Linage 3,Linage 1 and Linage 5,respectively.Further comparison of the Amino acids variation sites of GP5 revealed that the variation sites were concentrated in the signal peptide region(aa 1-26),the first hypervariable region(aa 32-36)and the second hypervariable region(aa 57-62).In the meantime,aa 117-131 and aa 181-200 were found in the five epitope regions(aa 37-45,aa 36-52,aa 117-131,aa 149-163 and aa 181-200)of the GP5 protein Epitope region differences in amino acids more variation.From the positive samples of pig farm which outbreak of “abortion strom”,we found a PRRSV variant,isolated and designated JS2014.Based on the sequence analysis of genetic evolution,JS2014 showed high homology with JXA1(94.9%).The further analysis of phylogenetic showed JS2014 was a potential natural recombinant,and four recombination events have taken place within JS2014(The recombination events took place in 8757 nt-9613 nt,12210 nt-12490 nt,12869 nt-13094 nt and 13880 nt-14707 nt).JXA1-R and QYYZ are two putative parental-like strains.By the test of pathogenicity in piglets,it showed that JS2014 was milder than JXA1,but significantly higher virulent than QYYZ.In this study,we also analyzed the protective effect of commercial vaccines(JXA1-R and Ingelvac? PRRSV MLV)against JS2014 strain.The results showed that JXA1-R vaccines had better protective effects on JS2014 strain.