News brief

Scientists detected antibodies against the H5N1 strain of highly pathogenic avian influenza (HPAI) in four polar bears in East Greenland in 2025, consistent with previous identification of the virus in birds along linked migratory pathways.

A team led by University of Inland Norway researchers analyzed heart blood collected from 28 polar bears harvested in subsistence hunts in 2024 and 2025, publishing their findings yesterday in Emerging Infectious Diseases.

Deceased, infected wild Arctic mammals were reported in Alaska in 2023 and 2024 (H5N1) and in Svalbard, Norway (H5N5), in 2026. These detections, along with the animals’ nutritional and cultural significance to Indigenous people, highlight the need for ongoing surveillance in these regions, the authors of the new study noted.

“Seasonal bird migrations to Arctic nesting grounds create a hot spot for HPAI outbreaks, amplifying interspecies interactions and the risk for viral reassortment and dissemination across migratory flyways,” they wrote.

The team screened 109 polar bear plasma samples collected from 2016 to 2025 for antibodies against all influenza A viruses. They found none before 2024, but that year, three of 14 samples they tested showed positive signals on enzyme-linked immunosorbent assay (ELISA), rising to six of 14 in 2025.

Climate warming and the subsequent loss of sea ice leads to increased time spent on land and exposure to terrestrial pathogens through the exploitation of new food sources.

Further screening of all nine positive samples and three negative samples with a hemagglutination inhibition assay revealed H5N1 antibodies in four bears that had tested positive on ELISA, suggesting survival after exposure to an HPAI virus in that clade.

The hunters reported no signs of illness in the bears, which the authors said suggests that the animals can recover from HPAI infection. While further research is needed into the route of infection, HPAI spillover into mammals usually happens during the ingestion of virus through consumption of infected birds or environmental contamination.

“Polar bears (Ursus maritimus) are Arctic apex predators that face increased challenges associated with their ecologic position at the interface between marine and terrestrial ecosystems,” the researchers wrote. “Climate warming and the subsequent loss of sea ice leads to increased time spent on land and exposure to terrestrial pathogens through the exploitation of new food sources.”