Virulent strain of avian flu detected in seals in Antarctic region

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The Antarctic seal is the latest species to be hit by a virulent strain of avian flu as the virus jumps from birds to wild animals around the world, increasing concerns it will adapt to infect mammals and humans more easily.

The UK’s Animal and Plant Health Agency said on Thursday that its experts had detected avian flu in seals and other animals on the sub-Antarctic island of South Georgia, which scientists concluded was most likely introduced by birds migrating from South America.

The spread to mammals of the virulent H5N1 strain, which was first detected in poultry and wild birds in the spring of 2021, has raised concerns that the virus will begin to adapt to mammals, boosting its zoonotic potential to spread to humans.

“Given Antarctica is such a unique and special biodiversity hotspot, it is sad and concerning to see the disease spread to mammals in the region,” said Prof Ian Brown, APHA’s director of scientific services.

Ashley Banyard, an avian flu expert at APHA, said the team had found no evidence of adaptation among seals on South Georgia, indicating that the virus was not transmitted from seal to seal, but rather from birds scavenged by them or through their exposure to bird excrement.

However, scientists have found signs of adaptation in mammals in other parts of the world. For example, scientists found evidence of mammalian adaptation following a severe outbreak among seals on the New England coast of the US in June 2022. Adaptation was also identified in sealions in Chile.

South America has been badly hit by the virus in recent months, leading to thousands of deaths of marine mammals in Peru, Brazil and Chile. Its spread to the Atlantic Convergence — the marine belt encircling Antarctica — will be a further cause of concern for epidemiologists.

“It’s a numbers game,” said Banyard. “At the start of an outbreak you might not see adaptation in mammals, but if there is continued exposure there may be adaptation.”

In July last year the World Health Organization warned that the “alarming rise in mammalian cases” of bird flu posed an increased zoonotic risk as it meant the virus could adapt to infect humans more easily. While the incidence of avian flu in humans is low, fatality rates are high.

The US Centers for Disease Control and Prevention said 19 human cases had been detected worldwide from January 2022 to the end of December 2023, with nine severe cases leading to five deaths. Almost all of the patients had been infected through contact with diseased poultry and there was no evidence of the virus spreading between people.

The virus was first detected in the sub-Antarctic region in October last year following the deaths of several skuas, predatory seabirds. During a three-week expedition, an APHA virology team detected the virus in elephant seals and fur seals, as well as in birds including brown skuas, kelp gulls and Antarctic terns.

However avian flu has caused less infection among captive and wild birds across the northern hemisphere over the past three months than it did during the autumns of 2021 and 2022. Just five outbreaks have been reported across the UK since October 1, 2023; there had been more than 360 outbreaks over the previous two years.

Sampling of seabirds also suggests that some species that had been hit particularly hard by H5N1 have developed some immunity to the virus.