Isolation And Identification Of Swine Influenza Viruses And Serological Investigation Of Swine Influenza From 2018 To 2020

Swine influenza(SI)is an acute and infectious respiratory disease of swine caused by swine influenza virus(SIV).The mortality rate is low when infected with SI alone,but it is significantly increased when infected by secondary or mixed infection with other pathogens,which causes huge economic losses to the swine industry.SIV is widespread in swine population all over the world.When these viruses coexist in swine,they may rearrange,change their genetic characteristics and pathogenicity,and then have the potential to trigger a human influenza pandemic.Therefore,timely monitoring of SIV to analyze its genetic evolution and prevalence is of great significance to the prevention and control of SI.In this study,5808 nasal swabs,198 lung and bronchus samples were collected from swine farms and swine slaughterhouses in Shandong,Henan and Hubei provinces.The virus was isolated by inoculating SPF chicken embryo allantoic cavity.A total of 21 strains of SIV were isolated,the isolation rate was 0.35%.All of them were H1N1 SIV by PCR.The isolated virus strains were divided into two genotypes,including 19 strains of triple-reassortant H1N1 viruses,derived its PB2,PB1,PA,NP and M genes from 2009 pandemic H1N1 influenza virus(pdm/09H1N1)lineage,HA and NA genes from(Eurasian avian-likes H1N1,EA H1N1)SIV lineage,NS gene from(Classical swine H1N1,CS H1N1)SIV lineage.Another 2 strains,derived its PB2,PB1,PA,NP,HA,NA,M and NS genes from pdm/09 H1N1 lineage.While isolating the virus,this study also collected 17865 swine serum samples from swine farms in different provinces such as Shandong,Henan,Jilin,Liaoning,and Shanxi et al.EA H1N1 antigen,pdm/09 H1N1 antigen and H3N2 SIV antigen were used to detect serum samples by HI test,the total seropositivity rate was 52.14%,of which the positive rates of EA H1N1,pdm/09 H1N1,H3N2 SIV,EA H1N1+pdm/09 H1N1,EA H1N1+H3N2 SIV,pdm/09H1N1+H3N2 SIV,EA H1N1+pdm/09 H1N1+H3N2 SIV were 28.89%,9.05%,0.07%,14.01%,0.07%,0.02% and 0.04%,respectively.From the above data,it can be seen that seropositivity is common in swine population.The seropositivity rate of EA H1N1 is the highest in single SIV infection,and the seropositivity rate of EA H1N1+pdm/09 H1N1 is highest in two or three s of SIV infection.In this study,the genetic evolution and key amino acid sites of isolated SIV were analyzed.At the same time,the serum in the swine population was tested.The results of the study have greatly enriched the content of SI molecular epidemiology in China and deepened our understanding of the current status of SI epidemic.The prevention and control of SI provides a theoretical basis.