Isolation and Identification of H9N2 Subtype Avian Influenza Virus in Chicken Embryos

Among 50 eggs from a meat-type parent breeder chicken flock with egg dropping,1 embryo was dead at 9 d after incubation,which of allantoic fluid had′t hemagglutination activity,but after one passage in embryo,the allantoic fluid showed hemagglutination activity.By hemagglutination inhibition(HI) test against Newcastle disease virus(NDV),H5 and H9 subtype avian influenza virus(AIV),the agent for HA activity in allantoic fluid of dead embryos were identified as H9 subtype AIV and designated as strains ZKH90901.HA and NA genes were amplified by RT-PCR,then were cloned into pMD18-T vector and sequenced.The results showed that ZKH90901 was the H9N2 strain of avian influenza virus,The cleavage site of HA gene was KSGR↓GLF,it still belonged to low pathogenicity strain.This is the first report of isolation of H9N2 subtype avian influenza virus from eggs in China.