Multiple introductions of highly pathogenic avian influenza viruses into the High Arctic: Svalbard and Jan Mayen, 2022-2025.

Between 2022 and 2025, highly pathogenic avian influenza viruses (HPAIVs) of clade 2.3.4.4b, including four distinct H5 Eurasian (EA) genotypes, were detected in wild birds and mammals in the Svalbard Archipelago and on the island of Jan Mayen. We describe their epidemiology and genomic characteristics to improve understanding of HPAIV occurrence and transmission in the High Arctic. The initial cases in 2022 occurred during summer and involved a glaucous gull (Larus hyperboreus) and great skuas (Stercorarius skua) on Svalbard and Jan Mayen, representing the first detections of HPAIVs in the High Arctic. Three HPAIV genotypes were identified: EA-2020-C (H5N1), EA-2021-AB (H5N1) and EA-2021-I (H5N5). In 2023, HPAIVs were detected in a broader range of bird species and retrospectively in an Atlantic walrus (Odobenus rosmarus rosmarus) as reported by another research group. Genotypes identified in 2023 were EA-2020-C (H5N1), EA-2021-I (H5N5) and EA-2022-BB (H5N1). No cases were reported in 2024. In 2025, EA-2021-I (H5N5) was detected in Arctic foxes (Vulpes lagopus) on Svalbard, without preceding detections in wild birds. The foxes exhibited neurological symptoms and necropsy of one individual revealed the presence of feathers in its stomach. All sequenced viruses from the Arctic foxes uniquely carried the combination of PB2-E627K and PB1-H115Q, previously associated with mammalian adaptation. The detection of multiple genotypes indicates repeated and independent introductions of HPAIVs into these regions. The co-circulation of genetically distinct virus strains in areas of high bird density further suggests that Arctic breeding grounds may facilitate local viral amplification, reassortment and subsequent dissemination along migratory flyways, including transcontinental spread.