Objective To analyze molecular tracing and evolutionary characteristics of H9N2 avian influenza virus (AIV) strains isolated from two human cases and related environmental samples collected from live poultry markets (LPMs) in Changsha City in April 2025, provide scientific basis for avian influenza prevention and control.
Methods Gene sequencing was performed on H9N2 AIVs obtained from throat swabs of the two cases and environmental samples. Genetic evolution analysis on HA and NA genes, homology, receptor-binding specificity, protein activity, drug resistance, and N-glycosylation patterns were focused.
Results A total of 10 H9N2 avian influenza virus (AIV) gene sequences were obtained, including 1 whole genome. Homology analysis revealed that the HA gene was most similar to strains isolated from Fujian Province, while the NA gene was most similar to isolates from Fujian and Chongqing. HA gene belonged to the Y280-like h9.4.2.5 lineage, featuring a cleavage site of PSRSSR ↓ GLF. The receptor-binding site harbored Q226L and Q227M substitutions, and multiple antigenic mutations were observed compared to Y280-like vaccine strains. N-glycosylation site prediction identified 7 potential sites in all strains. All NA gene exhibited a deletion at amino acid positions 55-57 in the stalk region. Key active-site mutations (K135E, I145T) were mutanted, along with one or more substitutions in head epitopes, but no antiviral resistance markers were found. N-glycosylation analysis revealed 4 potential sites in 9 strains and 3 in 1 strain, the latter possibly linked to an N78D substitution upon sequence alignment.
Conclusion The H9N2 avian influenza virus exhibited diverse mutations in key sites and functional domains detected in Changsha in April 2025, with multiple transmission chains spreading locally. Multifaceted measures should be strengthened to enhance epidemic control and prevention.