Genetic evolution and pathogenicity analysis of two strains of duck-originated H6N2 subtype avian influenza viruses isolated in Guangxi on BALB/c mice

Objective:To investigate the molecular genetic characteristics of duck-originated H6N2 subtype avian influenza viruses isolated in Guangxi and evaluate their pathogenicity to mammalian BALB/c mice.Methods:Two strains of duck-originated H6N2 avian influenza viruses A/DK/GX/3101/2018 (GX3101) and A/DK/GX/5220/2018 (GX5220) isolated in Guangxi were selected to analyze the nucleotide homology and genetic evolution of the full-length genome by gene sequencing and genetic evolutionary analysis.Receptor binding specificity was used to analyze the receptor binding characteristics of the two viruses, and BALB/c mice were used to evaluate the pathogenicity of duck-originated H6N2 viruses.Results:Two strains of duck-originated H6N2 were derived from the Eurasian lineage.The HA cleavage site of viruses was PQIETR/GL, belonging to the low pathogenic avian influenza viruses.Amino acid mutation of E190V was found in the amino acid site of HA protein, and both strains recognized and bound avian-type SAα-2, 3 Gal receptors.After virus inoculation, the viruses were isolated and cultured positively in the lung tissues of mice, and inflammatory cell infiltration and structural integrity of alveolar structure were observed in the lung tissues of mice.Immunohistochemical detection of virus antigen showed that the lung tissues of mice inoculated with GX3101 viruses were positive for influenza virus nuclear protein (NP).Conclusion:The duck-originated H6N2 strains isolated in Guangxi have the characteristics of avian influenza viruses, and can directly infect mammalian mice without adaptation across the interspecies barrier so that the epidemic and evolution of influenza viruses H6N2 in poultry should be closely monitored.