Identification And Immunogenicity Analysis Of Six Strains Of Chicken H9 Subtype Avian Influenza Virus

In the early 1990 s,the Avian influenza virus(AIV)was first identified in Italy.Today,the virus has spread throughout the world.The virus mainly infects all kinds of poultry,waterfowl,and migratory birds.It also spreads between human and lower mammals.In 1994,Chen Bolun.isolated H9 subtype in affected chickens.In the past 20 years,a large number of H9 subtype avian influenza epidemics have been reported in various regions of the country each year.The virus has mainly caused sluggish growth of poultry,difficulty in breathing,and decreased egg production,which has seriously affected the healthy development of China's aquaculture industry.In order to understand the genetic variation of the H9 subtype avian influenza viruses that has been circulating in recent years in China,we investigated the virus isolation of suspected H9 subtype avian influenza viruses collected in different provinces from 2014 to 2015.Through virus identification and sequence determination,we analyze the genotypes and genetic variation of the currently circulating H9 subtype avian influenza virus.Moreover,through serum cross-inhibition experiments,we analyze the antigenic differences between H9 subtype avian influenza viruses isolates and H9 subtype avian influenza viruses vaccine strains to reveal the prevalence of the H9 subtype avian influenza viruses in China in recent years.The results of this study indicate that the six strains of avian influenza viruses isolated from 2014 to 2015 were all H9 subtype avian influenza virus strains.Through HA gene amplification and sequence alignment analysis,the HA sequences of the isolates were close to the sequences of H9 subtype avian influenza lineage 4.2.5 and had a farther distance to H9 subtype avian influenza vaccine strain F and SS(lineage 4.2.3).Through the comparison of the amino acid sequence of HA sequence,the glycosylation sites of the isolates and the F and SS vaccine strains are quite different.And there is no continuous basic amino acid insertion near the HA protein cleavage site(position 335~343).It means the isolates meet the molecular characteristics of the low pathogenic avian influenza virus.The results of serum cross-inhibition test showed that the HI value of the H9 isolates and the vaccine strains differed significantly in this study.The antigenic difference coefficient(R value)of WS-JL strain and WS-HD strain to the vaccine strains F and SS was lower than 0.125 which indicated the difference in antigenicity was significant.This study provides an important reference for the prevention and control of H9 subtype AIV in China.