Objective To analyze the genetic evolution characteristics of H9N2 subtype avian influenza virus in external environment in Anhui province from 2019 to 2021.
Methods A total of 383 positive samples of H9N2 subtype avian influenza virus detected in the etiological surveillance for avian influenza in external environment in Anhui were used, and 21 strains of virus were isolated and cultured in chicken embryos. The whole genome was sequenced after one-step ordinary real-time PCR amplification, and a phylogenetic tree was constructed with bioinformatics software to analyze its genetic evolution characteristics.
Results The 21 H9N2 virus strains all belonged to G57 genotype, the hemagglutinin (HA) gene fragment evolved from JN/99 genotype, the neuraminidase (NA) gene originated from G9 genotype, the matrix protein (MP) gene originated from G1 genotype, the nuclear protein (NP), non-structural protein (NS), polymerase acid prorein (PA), polymerase basic protein 1 (PB1) gene originated from F/98 genotype, and the polymerase basic protein 2 (PB2) gene fragment evolved from ST/7488 genotype. HA cleavage site showed low pathogenic molecular characteristics, and there were important amino acid site mutations. Q226L, H183N, T189D, A190T amino acid mutations occurred in HA protein. 62–64 deletion occurred in the stem of NA protein. Most strains had no PB2-E627K mutation, and all the strains had no D701N mutation. The PA protein of all the strains had 356R and 409N amino acid mutations, and the M2 protein of all the strains had S31N amino acid mutations.
Conclusion Avian influenza A (H9N2) virus isolated from external environment in Anhui from 2019 to 2021 belonged to a multiple source reassortant strain, and has the molecular characteristics related to the gradual adaptation to mammalian hosts. It is necessary to pay close attention to the pathogenic evolution of the virus.