Surveillance for influenza A virus H5-specific antibodies in Canada Geese (Branta canadensis) in Pennsylvania

Wild waterfowl serve as reservoirs for low pathogenic (LP) avian influenza viruses (AIV), maintaining a diversity of viral subtypes; however, infection with the H5 subtype has historically been uncommon in most species. This has changed with the emergence of H5N1 highly pathogenic (HP) AIV in North America during 2021–2022, substantially altering AIV ecology in wild birds.

Prior to H5N1 HPAIV’s emergence in North America, Canada geese (Branta canadensis) exhibited high exposure to H5 LPAIV relative to other waterfowl. During 2009–2012, 24% (20-28%) of Canada geese sampled in Pennsylvania during June had antibodies to AIV nucleoprotein (NP). Though antibodies to multiple hemagglutinin subtypes were detected, the most common was H5.

To assess changes in AIV exposure following H5N1 HPAIV’s introduction, blood samples from Canada geese throughout Pennsylvania were collected in June 2025, with antibodies to AIV NP detected in 33% of the geese. Among NP-seropositive samples, 52% had H5 antibodies. Of these, 48% reacted to a North American H5 LPAIV antigen, 18% to a Eurasian H5 HPAIV antigen, and 14% to both antigens. Additionally, among samples positive to both H5 antigens, 75% had Eurasian H5 antibody titers that were equal or higher than North American.

These results indicate that Canada geese in Pennsylvania are exposed to H5N1 HPAIV, although seroprevalence remains lower than that associated with historic North American H5 LPAIV. Collectively, these findings improve understanding of H5 AIV exposure and immunity in Canada geese and clarify the role of this species in the evolving epidemiology of H5N1 HPAIV.