Interannual differences in common eider duck exposure to avian influenza viruses at an Arctic colony

Avian Influenza viruses (AIVs) regularly circulate among migratory birds, but starting in late 2021 an incursion of highly pathogenic AIV (HPAIV; H5N1 clade 2.3.4.4b) was detected widely in North American wild birds. Understanding exposure of migratory birds to AIV can be assessed through detection of anti-AIV antibodies, which indicate prior infection and survival. We used archived plasma samples from a long-term population monitoring programme to examine trends in prior AIV infection (as indicated by antibody detection) in female common eider duck (Somateria mollissima borealis) across years pre- and post-HPAIV detection in Canada (2018, 2019, 2022, 2023 and 2024). Anti-AIV antibodies have been assessed at this colony previously; therefore, we also combined the results from our analyses with previous data to extend the temporal trend analyses back to 2007. While we found that anti-nucleoprotein (NP) antibody positivity was relatively high across all five years, with observed proportions of seropositive females ranging from 76.9% (in 2019) to 100% (2018, 2023 and 2024), we found that levels of detections of anti-NP antibodies have been generally higher since 2011, with lower levels observed in earlier years (e.g. 2007). Anti-H5 antibody positivity levels increased significantly between 2019 and both 2023 and 2024, reflecting the likely change in exposure with the occurrence of the 2021 HPAIV H5N1 incursion in North America. We found no differences in annual anti-H7 antibody positivity levels. Our results demonstrate that Arctic-breeding common eider ducks have experienced varying exposure to AIV over the study period, with increasing exposure to multiple types of AIV based on an increase in antibody detections in recent years.