Epidemiological Investigation Of Pathogenic Porcine Reproductive And Respiratory Syndrome In Parts Of Northeast Of China From 2014-2017 And The Comprehensive Control

PRRS is caused by porcine reproductive and respiratory syndrome virus(PRRSV),is recognized as one of the most serious infectious diseases in swine industry.In 2006,PRRS broke out in a large area in China,causing significant economic losses and aroused great attention.In order to study the prevalence of PRRSV in northeast China in recent years,this study investigated the molecular epidemiology of PRRSV etiology and serology in large-scale pig farms in Northeast China from 2014 to 2017.According to RT-PCR amplification of specific primers of Nsp2 and ORF5 genes in northeastern region from 2014 to 2017,we found a 769 bp Nsp2 gene amplified fragment and a 603 bp ORF5 amplified fragment.A total of 107 out of 501 disease-positive materials,the overall positive rate was 21.36%.The total positive rate of disease in Liaoning was 20.52%,that in Jilin was 21.42%,and that in Inner Mongolia(Chifeng)was 23.07%.This indicates that there are PRRS related strains in the study materials.The 12 strains were divided into in this study,one of the strains of BLCB(BoluoChiBu)NXX20160605 isolated in this study could induce CPE in the culture plate of Marc-145 cells and green fluorescence was observed in indirect immunofluorescence assay(IFA)of infected Marc-145 and PAM cells.And phylogenetic tree analysis of the vaccine recombinant strains,cell tests showed that the strains have a certain degree of virulence.In this study,homology analysis of nucleotides of Nsp2 of the strain of PRRSV detected from 2014 to 2017 with the selected reference strains showed that nucleotide homology of Nsp2 to each other was 80.8%-100%,GP5 Homology analysis showed that the nucleotide homology between PRRSV strains was 82.1%-100%.Analysis of the genetic evolutionary tree of Nsp2 and GP5 combined with the vaccination status of pig farms showed that there were mixed infections of vaccine virus,NADC30 strain,mutated wild virus and QYYZ strain to varying degrees in the pig farm in this study.Using ELISA kit,4143 serums of PRRS vaccine immunized pigs collected from 2014-2017 were detected in this experiment,with a total of 3771 positive and the positive rate was 91.02%.The positive rate of serum samples reached a high level,the positive rate of serum samples in Liaoning was 90.71%,the positive rate of serum samples in Jilin was 90.47%,and the positive rate of serum samples in Inner Mongolia(Chifeng)was 91.85%.The overall positive rates of antibody in Liaoning,Jilin and Inner Mongolia from 2014 to 2017 were not significantly different from those in other years.The positive rate of antibody in 2017 was slightly lower than that in 2014,2015 and 2016.This may be related to the pig farm replacement.In the same year,antibody positive rates in different regions are also closer.On the whole,the vaccines in the area are more immunized.The S/P data showed that the immunization effect in 2016 was better than that in other years,and the overall immune effect in Inner Mongolia Dong Chifeng was better than that in Liaoning and Jilin.On the basis of mastering the etiological and serological investigations,PRRS can be used to prevent and control pig farms by comprehensive prevention and control measures.The comprehensive prevention and control measures of PRRS in pigs in this study include biosafety,feed nutrition,feeding and management,vaccine immunization and purification schemes.