The highly pathogenic avian influenza (HPAI) H5N1 has breached Antarctica’s natural barriers. This aggressive strain of bird flu, responsible for widespread mortality in bird populations globally, spreads rapidly and can cause high rates of death. Its arrival in this remote ecosystem represents a significant threat to the unique and densely concentrated wildlife that resides there.
The Virus’s Journey to the Antarctic
The pathway for HPAI H5N1 to the frozen continent was the annual movements of migratory birds. Genetic analysis confirms the virus traveled from South America, where it had caused significant die-offs. These birds acted as the primary vectors, carrying the virus across the Drake Passage to Antarctic and sub-Antarctic feeding and breeding grounds.
Among the first species implicated in this transmission are brown skuas, predatory seabirds known for their long-distance travel. The initial confirmation of the virus in the Antarctic region came in October 2023 on Bird Island, South Georgia, a sub-Antarctic island.
The first suspected cases within the official Antarctic Treaty Area were reported in December 2023. These observations were made near Argentina’s Orcadas Station and involved Antarctic skuas. By February 2024, the virus’s presence on the Antarctic Peninsula itself was definitively confirmed through laboratory testing.
Wildlife Affected by the Outbreak
The H5N1 virus has infected a broad range of species in Antarctica, impacting both birds and marine mammals. Avian species have been hit particularly hard, with significant mortality in predatory and scavenging birds. Skuas, among the first to test positive, have experienced substantial losses, partly due to their behavior of feeding on the carcasses of infected animals, creating a cycle of transmission.
Other affected bird species include kelp gulls and Antarctic terns. While there were initial fears for the continent’s penguin populations, large-scale die-offs have not yet been reported among species like gentoo or Adélie penguins. However, the situation remains under close observation by researchers.
The outbreak has also crossed over into mammalian populations. Southern elephant seals and fur seals have suffered significant mortality events. The virus was confirmed in these pinniped populations in the sub-Antarctic islands and the Antarctic Peninsula, with reports of thousands of deaths. The high viral loads found in tested animals indicate a high degree of infectiousness among these populations.
Consequences for the Antarctic Ecosystem
The arrival of HPAI H5N1 threatens the Antarctic ecosystem because its wildlife is “immunologically naive.” Having evolved in extreme isolation, these animal populations have no prior exposure or built-up immunity to this virus. This lack of defense makes them exceptionally vulnerable to widespread mortality, with some seabird colonies in other parts of the world seeing losses of up to 60%.
The death of key species could trigger cascading effects throughout the Antarctic food web. For instance, skuas are significant predators of penguin eggs and chicks; a sharp decline in the skua population could alter the reproductive success of penguin colonies. Similarly, a mass die-off of seals would remove a major predator and a source of nutrients for scavengers, disrupting the ecological balance.
The dense breeding colonies of both birds and seals create an environment where the virus can spread with speed and efficiency. A single infected animal returning to a colony can initiate an outbreak that affects thousands of individuals. The long-term consequences could include major breeding failures and lasting damage to the continent’s biodiversity.