Domestication Of Mouse-adapted Strains Of Seasonal Influenza B Victoria Virus And Study On The Pathogenicity Of Mouse-adapted Strains

The study of the determinants of pathogenicity and virulence of Influenza B virus(IBV)on non-human mammalian hosts is crucial.Animal models are available,but the lack of animal models for studying IBV limits the research on the pathogenicity and transmission factors of influenza B,as well as the evaluation of the effectiveness of animal antiviral drugs and vaccines,so this study uses the 2019 Northern Hemisphere recommended by WHO Seasonal influenza B virus vaccine strain B/Colorado/06/2017-like virus(B/Victoria lineage),referred to as IBV-WT(wild type Influenza B virus strain,IBV-WT)strain.The IBV-WT strain was used to infect mice at103.83 MLD50/50 μL,and the mice were sacrificed at 5 dpi(Days post infection,Dpi),and the lung supernatant was taken to infect the next generation of mice.Mouse-adapted influenza B virus(IBV-MA)was obtained in the 20 th generation.To analyze the genetic characterization of seasonal Victoria influenza B virus after adaptation to non-human mammals,and to compare the virulence of IBV-WT and IBV-MA,to confirm the increased virulence of MA strains in mice and to study its adaptation Pathogenesis in mice.At the same time,in order to detect the replication of the virus during the passaging process,the replication virus detection primers and probes were designed according to the NS2(Non-structural,NS2)protein of the influenza virus during the passaging experiment.The results showed that the mice were infected with the supernatant of the lung grinding supernatant of the MA generation slaughtered mice,and the mice showed severe clinical symptoms: curled up,messy coat,slow movement,and all died at 6dpi.The genetic characterization during its adaptation to mice was analyzed.Genome analysis showed that compared with WT,the MA strain had five mutations,namely I188 T in the HA gene,K358 E in the NA gene,and S157 G and V431 I in the PA gene..102TCID50/50μL infected mice were fixed with IBV-WT and IBV-MA at the same time,and the mice were sacrificed at 3 dpi,5 dpi,7 dpi,9 dpi and 14 dpi time points,respectively.Through the comparison of body weight changes,lung virus titers and pathological sections,it was found that the weight loss of the M21 group was more obvious than that of the IBV-WT group,and the virus titers in the target organs of the mice were higher.At the same time,a q RT-PCR method for the detection of seasonal Victoria influenza B virus genome and replicating subgenes was successfully established.