Surveillance of avian influenza viruses in Hebei Province of China from 2021 to 2023: Identification of a novel reassortant H3N3.

Avian influenza remains a global public health concern for its well-known point mutation and genomic segment reassortment, through which plenty of serum serotypes are generated to escape existing immune protection in animal and human populations. Some occasional cases of human infection of avian influenza viruses (AIVs) since 2020 posed a potential pandemic risk through human-to-human transmission. Both east-west and north-south migratory birds fly through and linger in the Hebei Province of China as a stopover habitat, providing an opportunity for imported AIVs to infect the local poultry and for viral gene reassortment to generate novel stains. In this study, we collected more than 6000 environmental samples (mostly feces) in Hebei Province from 2021 to 2023. Samples were screened using real-time RT-PCR, and virus isolation was performed using the chick embryo culture method. We identified 10 AIV isolates, including a novel reassortant H3N3 isolate. Sequencing analysis revealed these AIVs are highly homologous to those isolated in the Yellow River Basin. Our findings supported that AIVs keep evolving to generate new isolates, necessitating a continuous risk assessment of local avian influenza in wild waterfowl in Hebei, China.