Isolation And Identification Of Epidemic Strains Of Avian Influenza In Hebei Province And Study On The Antiviral Effect Of Lentinan

This study aims to isolate and identify the epidemic strains of avian influenza virus in poultry farms,Hebei Province in 2019.We selected representative ones for genetic evolution analysis,evaluated the pathogenicity and transmission ability of the virus to mice,and initially explored.The protective effect of the lentinan on mice infected with the virus.This study provided new ideas for influenza prevention and controling healthy breeding.The experiment 1:Isolation and identification of avian influenza virus.The raws disease materials were isolated and obtained to 6 strains of H9N2 virus and 5 strains of H5N6 virus through chicken embryo blind transmission and sequencing.In these virus,A/chicken/Hebei/078/2019(H9N2)and A/chicken/Hebei/089/2019(H5N6)were selected strains to carry out follow-up tests.The results of genetic evolution analysis showed that the HA and NA genes of HB078 had a single genetic evolution source.The genes belong to the Y280-like branch.The phylogenetic tree branches of HA and NA genes of Hb 089belong to the Eurasian lineage,which may be homologous to the mink,and has the risk of infecting mammals.The experiment 2:Study on the pathogenicity of HB 078 and HB 089 in mice.Infect mice through nose drops to monitor.The changes in the mice body weight and lung lesions were monitored.The results showed that the mice infected with the HB 078 avian influenza virus recovered after a slight weight loss,and the mortality rate of the mice was 0.Meanwhile,the weight the mice infected with the HB 089 avian influenza virus dropped drastically on the 3rd day,and the mortality rate of the mice reached 100%.The HB 089 caused caused severe viral acute lung injury.The Experiment 3:Study on the risk of transmission of HB 078 and HB 089 among guinea pigs.Using the three-to-three model,The guinea pigs were divided into direct contact transmission group and indirect contact transmission group,and the guinea pigs model of the transmission ability of influenza virus was established.Hb 078 and Hb 089 can be transmitted by direct contact,with an efficiency of 66.7%,according to the test of guinea pig nasal rinse.The experiment 4:In this study,a mouse model of avian influenza virus Hb 078 was used to verify the inhibitory effect of lentinan on the current circulating strains in breeding farms.The BALB/c mice were divided into six groups:blank control(BC),negative control(NC)(virus model group),positive control(PC)(oseltamivir phosphate group),low,medium,and high dose lentinan groups.Changes in body weight,lung index and inhibitory rate,and changes in pneumonic factors of mice were measured and obtained.The results showed that the middle dose of lentinan could effectively inhibit the weight loss of the mice caused by HB 078 avian influenza virus infection.On the 3rd day after infection,the viral load in the lung tissue of the mice was extremely significantly reduced to 10^3.0 EID₅₀/m L,P<0.01.On the 5th day after infection,the lung index decreased significantly to 1.36±0.16,P<0.05,and the lung index inhibition rate increased to49.08%.Furthermore,the expression of INF-?gene in lung tissue was extremely significantly increased,and the expression level of TNF-?gene is extremely significantly reduced,P<0.01.Based on the above results,the results of this study show that:(1)The main subtypes of avian influenza viruses circulating in poultry farms in Hebei Province are H9N2 and H5N6;the two representative avian influenza viruses can both be unadapted under laboratory conditions Directly infect mice and guinea pigs,and HB 089 strain(H5N6)is more pathogenic to mice;the two strains of viruses can be efficiently transmitted between guinea pigs through direct contact,but they do not have the ability to transmit through air;(2)Lentinan is mainly By reducing the viral load in the lung tissue of mice,reducing lung inflammation,regulating the expression of cytokines in lung tissue,and alleviating the suppression of the mouse's specific immune function against influenza virus,it ensures the function of the body's antiviral mechanism,and then achieves the The protective effect of mice infected with avian influenza virus.