Diversified reassortant H9N2 avian influenza viruses in chicken flocks in northern and eastern China.

According to our previous study of the M genes of H9N2 avian influenza viruses (AIV) in infected chickens, A/Quail/Hong Kong/G1/97 (G1 97)-like M genes newly emerged in northern and eastern China in addition to the existing A/chicken/Hong Kong/Y280/97 (Y280)-like lineage M genes. To systematically track the genesis and evolution of H9N2 viruses in this region, whole genome sequences of seventeen H9N2 isolates were obtained and their phylogenetic properties were determined. Phylogenetic analysis revealed several newly emerged lineages of gene segments in addition to the Y280-like and A/chicken/Shanghai/F/98(F 98)-like lineages, which are prevailing in northern and eastern China according to previous reports. Reassortments among these gene segments generated five novel genotypes of H9N2 viruses that have not been reported before in China. The emerging genotypes of H9N2 viruses in this region indicate that H9N2 virus genes undergo active evolution, particularly their internal genes, which raises concern for their likely contribution to gene reassortment and production of AIVs with new properties. Our study provides valuable insight into the prevalence of H9N2 viruses in northern and eastern China and demonstrates the need of long-term monitoring of the evolution of H9N2 AIV.