Epidemiological and Genomic Characterization of H5 Subtype Avian Influenza Viruses in Jining City, 2024–2025

Objective: The aim of this study was to characterize the epidemiological features and whole-genome characteristics of H5 subtype avian influenza viruses circulating in Jining City during 2024–2025, and to provide scientific evidence for avian influenza prevention and control. Methods: A total of 748 poultry-related environmental samples were collected in March, June, September, and December of 2024–2025. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) was used to detect influenza A virus and H5 subtype viral RNA. H5-positive samples were subjected to whole-genome sequencing and analyzed using bioinformatics tools. Results: Among the 748 samples, the positivity rate of influenza A virus was 16.04% (120/748), and that of the H5 subtype was 8.16% (61/748). The H5 positivity rate in 2025 (11.88%) was significantly higher than that in 2024 (5.37%). Higher positivity rates were observed in March and December compared to June and September. Twelve complete H5 genomes were obtained, including nine H5N1 and three H5N6 strains. All HA genes belonged to clade 2.3.4.4b. Key mutations related to antigenic drift, replication and adaptation were detected in multiple viral proteins. Conclusions: The positivity rate of H5 subtype avian influenza viruses in Jining City showed an increasing trend during 2024–2025, with higher prevalence in winter and spring. The circulating strains predominantly belonged to clade 2.3.4.4b. Antigenic drift-associated mutations in the HA protein were identified in some strains, which may affect vaccine matching. Enhanced surveillance of H5 viruses and regular evaluation of antigenic compatibility between vaccine and circulating strains are recommended to mitigate potential risks posed by viral genetic variation.