Isolation and identification of H9N2 subtype avian influenza virus from chicken in Guangxi and its genetic evolution

ObjectiveThis study determined molecular genetic variation regularity of H9N2 subtype avian influenza virus(AIV)and its effects on public health safety of human so as to provide reference for the prevention and control of H9 subtype avian influenza(AI).MethodSuspected tissue samples were collected from one chicken farm in Guangxi, viral isolation was performed by inoculating SPF chicken embryo.The virus was preliminarily identified as H9 subtype AIV isolated strain.Then eight gene fragments isolated from H9 subtype AIV including HA,NA,PB2,PB,PA,NP,M and NS were sequenced,and their genetic evolution was analyzed.The biological characteristics of the isolated strain were also determined at the same time.ResultA H9N2 subtype AIV strain,named A/chicken/Guangxi/BT1/2016(H9N2),was successfully separated from the sick chicken population in Guangxi.The cleavage site of HA gene in A/chicken/Guangxi/BT1/2016(H9N2)was PSRSSR↓GLF,which had typical features of low pathogenic AIV(LPAIV)molecule.In genetic evolution relation,it belonged to 4.2.5 branch,and had some differences with the domestic H9N2 subtype AIV vaccine strains which belonged to 4.2.3 branch.The other seven genes were also derived from different AIV subtypes.The isolated virus strain A/chicken/Guangxi/BT1/2016(H9N2)could bind to α-2,3 sialic acid and α-2,6 sialic acid receptors,with the potential risk to infect human. Virus distribution was mainly concentrated in trachea,lung and spleen after it infected chicken,and the virus also could be released through the respiratory tract and digestive tract at same time.The virus was released from day 1 and peaked on the day 5 after the chicken was infected.ConclusionA/chicken/Guangxi/BT1/2016 (H9N2),isolated from Guangxi sick chicken population,belonged to LPAIV.It is a H9N2 subtype new virus created by different subtypes AIV.It can lead to the failure of chicken vaccine immunization and has the potential risk of infecting hu-man beings.