Pathogenicity And Transmissibility Of Influenza A (H7n9)Virus Isolated From Quail

H7N9 virus is a newly recombined Influenza A virus.In 2013,it was first discovered that it can infect people and cause severe respiratory syndromes,with extremely high mortality rate,posing a serious threat to global public health.At present,the previous research on the H7N9 subtype influenza virus has mainly focused on wild bird sources,poultry sources and other strains,and there is rare report on quail source studies.Therefore,research on the pathogenicity and transmission ability of Influenza A(H7N9)virus isolated from a Quail in Hebei province in 2018 can provide theoretical and technical support for the prevention and control of Influenza A(H7N9)in Hebei Province.The research contents are as follows:1.Isolation,identification and biological characteristics of a strain of quail-derived H7N9 subtype A Influenza virus A/quail/Hebei/CH06-07/2018(H7N9),(referred to as CH06-07 strain)from Hebei Province in 2018 was completed.The results of homology,amino acid mutation sites and genetic evolution analysis showed that except the strain with the highest nucleotide homology between PB2 gene and NP gene was of duck origin,the other genes(PB1,PA,HA,NA,M,NS)with the highest nucleotide homology are all of chicken origin.The strain with the highest homologous nucleotide homology is of chicken origin;the HA06 protein of' the CH06-07 strain has G186V mutation,the PB2 gene encodes the protein 1292V and K526R mutation,the PB1 gene encodes the protein I368V mutation,and the PA gene encodes the protein K356R and S409N mutation,M1 gene encoding protein has N30D mutation.M2 gene encoding protein has S31N mutation,NS gene encoding protein has P42S mutation(H3 number);the HA gene and NA gene of CH06-07 strain are placed in the Eurasian branch.The results of the receptor binding characteristics test showed that the CH06-07 strain not only possesses the a-2,3 sialic acid receptor binding ability,but also the ?-2,6 sialic acid receptor binding ability,which means that the CH06-07 strain has both the ability to infect birds and the potential to infect mammals.The results of EID50 measurement showed that the half chicken embryo infectious dose of CH06-07 strain was 108.87 EID50/mL.2.The pathogenicity of CH06-07 strains to the quail and mice were studied.The test results showed that the mortality of quails challenged by CH06-07 was 100%,and that of mice after challenge was 80%;the virus could be detected in multiple organs of the quail and mice.Flu-related lesions were observed in the lungs of quail and mice by HE staining,and virus antigens could be detected in the lungs of quails and mice by immunohistochemical.3.The transmission ability of the CH06-07 strain between quails and guinea pigs was studied,and an aerosol sample protocol based on the liquid impact microbial aerosol sampler(AGI-30)was established,which improved the H7N9 influenza virus aerosol sampling efficiency.The results showed that the CH06-07 strain has a very strong ability to spread between quails,and 100%transmission can occur.The third weather sol detoxification amount is significantly higher than the first day;the transmission efficiency of the CH06-07 strain between guinea pigs is three pass two.The amount of aerosol detoxification was highest on the first day,and then gradually decreased.4.A new aerosol-infected BALB/c mouse model was established in order to evaluate the pathogenicity difference of the two inoculation method,mice were challenged in lung by aerosol route using a liquid quantitative nebulizer or by intranasal inoculation.The results showed that compared with nasally inoculated mice,the lung weight of aerosol challenged mice was significantly reduced(P<0.05),the survival rate was also reduced,and virus titer in lung was significantly increased(P<0.05),and the pathological damage was more obvious.Compared with the traditional nasal challenge method,the quantitative aerosol challenge of lung fluid established in this study can increase the virus load in mice and improve the accuracy of evaluating the pathogenicity of Influenza A H7N9 virus.