Serological Detection And Evolutionary Analysis Of Epidemic Strains Of Classical Swine Fever Virus In Shanxi Province From 2018 To 2019

Classical swine fever(CSF)is an infectious disease caused by classical swine fever virus(CSFV).It is characterized by high fever,rapid infection and high mortality,leading a considerable economic loss in pig industry.In order to understand the prevalence of CSF in Shanxi province in recent years,this study was to investigate the positive ratio of CSFV antibody by blocking ELISA to evaluate the protective efficacy of CSFV vaccine to pigs.The serum samples collected from the slaughterhouse in 2019 were used to distinguish between wild CSFV strains and vaccine strains.The suspected samples from various regions of Shanxi were tested by CSFV RT-PCR to further determine the distribution of CSFV in Shanxi,and finally part of the positive samples was subjected to full-length sequencing of CSFV E2 gene to analyze the genotypes and mutations of the epidemic of CSFV strains in Shanxi.It can lay the foundation for the limitation of CSF in Shanxi.In this study,4567 sera samples from pig farms in 2018 and 3285 sera samples from 2019 were tested for CSFV antibodies,and 360 serum samples from slaughterhouses in 2019 were distinguished from wild CSFV strains and vaccine strains antibodies The results showed that the antibody positive ratio of CSFV was 85.64% in 2018,88% in 2019 and 4.44% in 360 serum samples.In addition,250 clinical samples from various regions of Shanxi Province were tested for RT-PCR of CSFV in 2019.The positive ratio of samples from Linfen city(36.49%)and Jinzhong city(31.82%)samples exceeded 30%,suggesting that it is necessary to strengthen the prevention and control of CSF.Finally,the full length of the E2 gene of CSFV collected from two positive samples was sequenced and analyzed.Comparing with the E2 sequences of different genotype strains in the NCBI database,and performing evolutionary tree analysis,it was showed that SX-1 and Hu B16-2015 are 97% homologous,belonging to the 2.1b subtype.SX-2 strain(vaccine Strain)is 99.4% homologous to the HCLV vaccine strain and belongs to type 1.1.In summary,the immunization of the classical swine fever vaccine in Shanxi was satisfied from 2018 to 2019,but there were still CSFV infections in some pig herds,implying the vaccine immunization failure occurred..Through the investigation of infection or immunization failure farms,it is found that immunization failure is mainly due to the poor environment in the farm.Therefore,we should pay more attention to the establishment of a better biological safety system in production practice,and design better scientific immunization procedures.