Evolution Analysis And Pathogenicity In Mice Of Swine Influenza Viruses Isolated From 2016 To 2018 In Shandong Province

Swine influenza?SI?is an acute,highly contagious,infectious respiratory tract disease caused by swine influenza virus?SIV?.Pigs are proposed as the"mixing vessel"of influenza viruses for having the sialic acid receptors of human and avian influenza virus co-infection of different avian,human or swine influenza viruses at the same time.It possible that the novel genotype or subtype viruses will be generated in pigs by genetic reassortment and obtain the potential ability to infect human and cause new worldwide pandemics.Therefore,it is of great public health significance to carry out the epidemiological investigation and pathogenicity study of SIV.To investigate the prevalence of SIV in Shandong province,a total of 5260 nasal swabs were collected from different slaughterhouses and pigs of farms during 2016 and 2018.Thirty-eight strains of H1N1 subtype SIV were isolated by 10 days embryonated eggs and identified by RT-PCR.Genetic and phylogenetic analysis showed that 21 strains viruses were divided into two different genotypes,including 18 strains of triple-reassortant H1N1 viruses,derived its PB2,PB1,PA,NP and M genes from 2009 pandemic H1N1?pdm/09 H1N1?viruses,HA and NA genes from Eurasian avian-like H1N1?EA H1N1?SIVS,NS gene from classical swine H1N1?CS H1N1?;Another 3 strains of triple-reassortant H1N1 viruses,derived its PB2,PB1,PA and NP genes from 2009 pandemic H1N1?pdm/09 HIN1?viruses,HA,NA and M genes from EA H1N1 SIVS,NS gene from CS H1N1.To know the pathogenicity of two different genotypes of H1N1 SIV,four viruses?SW/SD/LW16/17,SW/SD/TA25/17,SW/SD/TA95/17 and SW/SD/TA97/17?were chosen to evaluate their pathogenesis in BALB/c mice.six-week-old female BALB/c mice were infected with 10⁶ EID₅₀0 of respective virus by intranasal inocuLation.The pathogenicity of virus was evaluated by measuring the body weight loss of mice and virus replication titre in vivo and pathological histologic changes of lung after infection the viruses.The resuLts showed that 4 strains showed a certain pathogenicity in mice.After the virus infection,each group had a weight loss rate of more than 30 percent,and the mice were considered as dead after infection.The titration resuLts of the viscera showed that the virus was detected at the same time in the lungs and the turbinate,and the virus was not detected in the kidney,spleen and brain.The viral titers ranged from 7.92 log₁₀EID₅₀/mL⁹.13 log₁₀EID₅₀/mL in lungs,and from 3.63 log₁₀EID₅₀/m L⁶.29 log₁₀EID₅₀/mL in nasal turbinates.The above resuLts showed that different genotypes of H1N1 and different strains of the same genotype showed certain pathogenicity in mice.