| Avian influenza(AI)is caused by avian influenza virus(AIV)in a variety of birds(wild and poultry)and exhibits a mild respiratory symptoms or acute sepsis characteristics.Among many subtypes of avian influenza,H9N2 subtype influenza.Mainly infected poultry,wild birds,people,and so on.As the H9N2 subtype influenza virus belongs to the low pathogenic avian influenza,the infected wild birds often shows asymptomatic or slight symptom.As wild birds migrate,the virus is transmitted to different animals,causing the outbreak of the subtype influenza virus.Therefore,it is very important to control H9N2 influenza virus in wild birds.During molecular epidemiological investigation of wild avian influenza virus in 2016-2017 the whole genome amplification and sequencing of the isolated 22 strains of H9N2 influenza virus were carried out,and the genetic variation of H9N2 subtype influenza virus in wild birds was studied by phylogenetic analysis.The receptor affinity characteristics of 8 strains of H9N2 subtype avian influenza virus were identified and their binding characteristics were analyzed.At the same time,two kinds of commercialized H9N2 influenza inactivated vaccine were selected to evaluate protection efficiency of the current vaccine against the strains,which further provides suggestions for H9N2 influenza virus prevention and control.1.In 2016-2017,1194 samples of wild fowl feces and cotton swabs were collected from the wetland nature reserves.Ninety-six samples were positive for avian influenza virus,including 26 samples of H9 influenza,2 samples of H5 influenza and 9 samples of H7 influenza.The whole genome amplification and sequencing were conducted for 26 samples of H9N2 and 22 strains of wild birds in different time,and compared with the reference strain gene database,the evolutionary tree was plotted and the genetic variation was analyzed.The results showed that there were differences in the internal genes of the isolated strains.The isolates were in different branches,but all belonged to the Eurasian pedigree Y280-like.Although the evolutionary tree is complete,the H9N2 subtype of influenza strain has undergone gene rearrangement or recombination over time,resulting in genetic mutation.2.In order to study the receptor binding ability,8 strains of H9N2 subtype influenza virus were selected.The receptor affinity characteristics were identified by a solid phase enzyme test.The results showed that these 8 strains had the ability to bind with two sialic acid receptors.The binding ability of 3 strains with human sialic acid receptor was stronger than that of avian sialic acid receptor,which indicated that 3 strains was possible to infect human.3.In order to determine whether the current vaccine was effective in protecting chickens against the attack of H9N2 subtype influenza virus,we chose two kinds of vaccines to challenge 5 strains in the three branches.Determination of antibody and detoxifycation verified the effect of vaccine on virus protection.The results showed that vaccine immunization at 14 d reached the protection level of HI antibody(?4 log2).The antibody level of the two vaccines reached 8 log2 at day 21,with strong protection ability.The chickens were challenged with virus at day21.The results showed that the current commodity vaccines cannot fully protect against the H9N2 subtype influenza virus.In summary,H9N2 subtype influenza virus mainly affected wild birds and changed antigenicity.We should develop an effective vaccine as soon as possible to control the forthcoming outbreak.In order to reduce the occurrence of H9N2 influenza,we should pay close attention to the dynamics of the influenza virus,carry out epidemiological investigation,enhance feeding management,perform reasonable vaccine regime,and strengthen monitoring and control measures. |
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