bioRxiv | March 21, 2026
28 March 2026
The frozen isolation of the sub-Antarctic and Antarctica has been breached by a formidable adversary. A comprehensive study of the High Pathogenicity Avian Influenza (HPAI) H5N1 virus reveals that the pathogen has not only established a foothold in these remote ecosystems but is actively evolving and persisting across vast distances.
Researchers analyzed 104 novel viral genomic sequences collected across an 8,000-kilometer range, including the Antarctic Peninsula and several sub-Antarctic archipelagos. The study identified two distinct viral lineages responsible for the devastation:
- Clade I: Derived from avian-focused lineages in South America, this clade demonstrated long-distance, eastward circumpolar dispersal. Its movement patterns align closely with the rapid, wind-driven migrations of large petrels and albatrosses.
- Clade II: Originating from South American marine mammal lineages, this clade remained concentrated within the Scotia Sea area (including South Georgia and the Falklands), characterized by frequent back-and-forth transmission between islands.
The biological cost of this incursion has been staggering. On South Georgia, an estimated 47% of breeding female southern elephant seals, roughly 53,000 individuals, succumbed to the virus during the 2023/24 season. In the Falklands, black-browed albatrosses faced fatalities potentially reaching one hundred thousand, primarily among chicks.
Crucially, the study highlights that the virus is not static. Researchers observed lineage replacement dynamics, where successive versions of the virus became dominant by fixing known mammalian-adaptive mutations. Specifically, mutations such as PB2 D701N and Q591K were found to enhance viral replication in mammalian cells, raising significant concerns about the virus's long-term drivers of mammalian adaptation.
Perhaps most concerning is the evidence of local persistence. The virus re-emerged in the 2024/25 austral summer from lineages already present the previous year, suggesting it can survive the harsh Antarctic winter. This could occur through:
1. Environmental persistence in the freezing climate.
2. Sustained transmission among resident species like gentoo penguins.
The study concludes that the risk of H5N1 becoming endemic in the region is high. With scavenging seabirds acting as long-distance vectors, the threat of further spread to Oceania and other untouched polar regions remains a critical conservation and public health priority.
