Mass #mortality of southern elephant #seals during multi-species #outbreak of HPAI #H5N1 on sub - #Antarctic Heard Island

 

Abstract

High pathogenicity avian influenza (HPAI) has spread across the sub-Antarctic, causing significant wildlife impacts. We report its first detection in an Australian external territory, Heard Island and McDonald Islands, which supports over one million breeding seabirds and seals. Drone and ground surveys (October 2025, January 2026), combined with viral genome analysis, confirmed infection with Influenza A H5N1 clade 2.3.4.4b at Heard Island. Drone surveys revealed mass mortality in southern elephant seals, with 8,573 pups (62%) recorded dead across Heard Island by the final surveys. Mortality increased at an average rate of 5.6% per day in a subset of harems, and the highest observed mortality in a harem was 97%. Based on the average (76%) mortality in the final surveys, total estimated pup mortality at Heard Island was 13,359 (from a total population of 17,364 pups), though this may be an underestimate as mortality was ongoing at this time. HPAI was detected in six of nine species tested and, we suspect, led to elevated mortality in king and gentoo penguins. Phylogenetic analysis indicates the virus was introduced from Crozet Islands, with an estimated arrival around August 2025. These data show the continued easterly spread of HPAI around the sub-Antarctic, with severe but heterogeneous impacts across taxa. Our results demonstrate the value of drones for large scale monitoring, underscoring the need for continued and enhanced HPAI surveillance across the Southern Ocean.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.06.16.732752v1

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#Vaccination against #H5 HP #influenza virus leads to persistent immune response in wild king #penguins

 

Abstract

Since 2021, the panzootic of high pathogenicity avian influenza (HPAI) represents an increasing threat to wild vertebrate populations. In this context, recent vaccines developed for poultry could provide tools for the conservation of wild endangered birds populations. The king penguin (Aptenodytes patagonicus), a long-lived seabird breeding in dense colonies with an extended chick-rearing period, was identified as a possible surrogate species for a vaccination trial in a sub-Antarctic natural setting. We investigate here the immune response of king penguin chicks to a self-amplifying mRNA vaccine against a H5 HPAI clade 2.3.4.4b protein. Thirty chicks were vaccinated (primo- and boost-injections), 20 were kept as controls. Along 250 days of monitoring, vaccinated chicks showed a high and persistent immune response, granting a strong seroneutralisation capacity against the virus, up to fledging. No adverse effects were observed. The screening for antibodies against unspecific avian influenza viruses suggested that no natural infection occurred over the entire trial. The emergence of HPAI in the Southern Indian Ocean in October 2024 highlights the timeliness of such experimental tests. Our results show the vaccine could provide a powerful tool for mitigation and emphasises the need for studies considering ethical and practical issues of vaccination for wildlife conservation.

Competing Interest Statement

The authors declare as only conflict of interest that the work was partially funded by Ceva Wildlife Research Fund, an endowment fund created by Ceva Sante Animale, whose objective is to support applied animal health research projects contributing to wildlife conservation. Ceva Wildlife Research Fund had no role in the conceptualization, design, data collection, analysis, decision to publish, or preparation of the manuscript.

Funder Information Declared

French Polar Institute (IPEV), Project ECOPATH-1151, Project ECOENERGY-119

Agence Nationale de la Recherche, https://ror.org/00rbzpz17, ECOPATHS ANR-21-CE35-0016, WILDFLU ANR-2025-CE35-00XX

Ceva Wildlife Research Fund, CWRF2

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.09.06.674613v1

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