Ecological implications and lessons from high pathogenicity avian influenza H5N1 2.3.4.4b in Antarctica

High pathogenicity avian influenza (HPAI) H5N1 clade 2.3.4.4b poses a major global conservation threat, with Antarctic and subantarctic ecosystems at particular risk given the substantial ecosystem services driven by birds and mammals susceptible to HPAI in these regions. Understanding its impacts on threatened species and ecosystems, and the effectiveness of surveillance tools used by conservation managers, is critical. We surveyed seabirds and marine mammals at Dismal and Horseshoe Islands, Marguerite Bay, Western Antarctic Peninsula, in February–March 2025 for signs of HPAI H5N1 infection and mortality at the presumed southern limit of its spread, and sampled seabirds (primarily South Polar Skua Stercorarius maccormicki) using rRT-PCR and rapid antigen kits (VDRG® AIV Ag Rapid Kit 2.0). HPAI H5N1 was confirmed by rRT-PCR in 22 South Polar Skuas and one Kelp Gull Larus dominicanus. High skua mortalities were consistent with global trends, though many pairs were still breeding during surveys. No other species showed signs of infection despite observed environmental risk factors, although none were tested. Rapid tests showed 90% agreement with rRT-PCR results across 23 carcasses and seven live bird samples, indicating their potential utility for early detection. Practical implication: Sustained monitoring of Antarctic and subantarctic birds and mammals—integrating long-term monitoring data where possible, and where appropriate, implementing rapid antigen testing to enhance early detection (pending further evaluation and/or used with caution)—should be prioritised to improve our understanding of population-level impacts of HPAI H5N1 and track its ongoing global spread.