Evolution Analysis And Pathogenicity In Mice Of A H3N2 Swine Influenza Virus

Swine influenza?SI?is a zoonotic infection caused by swine influenza virus.Its clinical syndrome is mainly respiratory symptoms.Swine influenza virus belongs to the orthomaviridae family.The swine influenza virus can be classified according to the hemagglutinin which is condensed on the surface of the virion to the red blood cells and the neuraminidase glycoprotein which can release the virions adsorbed on the cell surface.There are 16 H subtypes and 9 N subtypes type.According to the difference of HA and NA,it can be divided into many serosubtypes.There are three subtypes of swine influenza,H1N1,H1N2and H3N2.Pig,avian and human influenza viruses can bind to sialic acid-containing glycoprotein receptors on porcine epithelial cells via lectin sites on HA proteins.The influenza virus gene is recombined in pigs to produce a new virus strain,and the influenza virus is easy to infect human cells.The consequences are very serious and cause serious harm to human life and health.Prevention and treatment of the disease that also poses great challenges and therefore has important public health implications.The disease has occurred in many countries and regions such as Asia,Europe,Europe,etc.,causing huge losses to the pig industry.Therefore,the investigation and research on swine influenza viruses is carried out to understand the genetic evolution and pathogenicity of swine influenza viruses in China,and it is particularly important for the prevention and control.In order to explore the prevalence of SIV in pigs in Shandong Province and surrounding areas and the basic characteristics of the strains,the laboratory collected nasal swab samples from different regions of Shandong Province in 2018 to inoculate 10 days old SPF chicken embryos for virus isolation.Hemagglutination test,RT-PCR amplification of NP or M gene,positively identified as swine influenza virus,followed by identification of virus subtypes using typing primers,identified as H3N2 subtype,named A/Swine/Shandong/JN1/2016?H3N2?.Eight fragments of the swine influenza gene were amplified by RT-PCR,and genome-wide sequencing and sequence analysis were performed.It was found that the PA,NS and M genes were derived from the 2009 H1N1 pandemic influenza virus?pdm/09 H1N1?branch,PB2,HA.And NA comes from the North American triple-influenza virus,the NP gene is from the European avian influenza virus,and the PB1 is from the human-type influenza virus.In order to understand the characteristics of the virus at a deep level,we used BALB/c mice as test animals,and infected 6-week-old female BALB/c mice with a dose of10⁶ EID₅₀/infected dose to observe the activity and death of the mice.The body weight of the mice was changed,the mouse organs were collected for virus titer measurement,and the histopathological changes of the mouse viscera were observed,and the characteristics of the strain were analyzed.The results showed that the mice decreased in activity,decreased feed intake,and decreased body weight.The titration of the organ detected viral replication in the lungs and turbinates,but no virus was detected in the kidneys,spleen and brain.The virus content in the lungs was between 2.25log₁₀EID₅₀/mL,and the virus content in the turbinate was between 1.75log₁₀EID₅₀/mL.In order to understand the infection of SIV in pigs in Shandong Province,764 sera were detected by HI antibody test.This provides a further theoretical and experimental reference for elucidating the characteristics of swine influenza virus.