Research note: Molecular characteristics and genetic evolution of H1N1 avian influenza virus from wild birds in Shanghai, China.

The H1N1 influenza virus is a major pandemic and seasonal pathogen with a broad host range, posing a substantial threat to human health and underscoring the need for continuous surveillance. Wild birds, as natural reservoirs of avian influenza viruses (AIVs), carry H1N1 strains capable of reassorting with other influenza viruses, which can drive pandemic emergence. The global migration of wild birds facilitates the spread of these viruses, and their interactions with poultry increase the risk of cross-species transmission, further amplifying the public health threat. However, knowledge of H1N1 genetic diversity in wild birds remains limited. Database analysis shows 80% of avian-origin H1N1 isolates come from wild birds across over 40 countries, mainly in North America, Europe and Asia. This study characterized the molecular traits and genetic evolution of four H1N1 AIVs isolated from common teal and spot-billed ducks during 2019-2021. Phylogenetic and sequence analyses revealed these viruses cluster into distinct lineages, divergent from mammalian H1N1 strains, with complex genetic origins involving frequent recombination and high diversity. Frequent wild bird-poultry transmission elevates zoonotic risks. Our findings highlight wild birds' critical role in H1N1 transmission and confirm their role as an H1N1 gene pool, emphasizing the need for sustained monitoring and research.