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Bird Flu Strikes Seals in Sub-Antarctica

An elephant seal.
Credit: Anchor Lee / Unsplash.
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High pathogenicity avian influenza (HPAI), commonly referred to as “bird flu”, has been confirmed in mammals inhabiting South Georgia, a remote island located in the South Atlantic Ocean that is a UK territory.

Bird flu confirmed in dead elephant and fur seals

In October 2023, several brown skua died on Bird Island, which lies off the nort-west tip of South Georgia. This raised suspicions that HPAI had been introduced to this remote area of the world.

Now, the Animal and Plant Health Agency (APHA) – an executive agency of the Department for Environment, Food and Rural Affairs of the UK – confirms that samples from dead elephant seals, fur seals, kelp gulls and Antarctic terns have tested positive for HPAI H5N1.

What is high pathogenicity avian influenza?

Avian influenza A viruses are categorized as either low pathogenicity avian influenza (LPAI) A viruses, or HPAI A viruses. The latter can cause severe disease and mortality in poultry. Though it is rare for avian influenza A viruses to infect people, five subtypes are known to have caused human infections, including H5 viruses.

From 2003 to 2023, the World Health Organization (WHO) documented 878 cases of HPAI H5N1 infection in humans.

Extent of the problem in the seal population unknown

Dr. Marco Falchieri from the influenza and avian virology team at APHA spent three weeks in South Georgia collecting samples, which were then tested and sequenced at a laboratory in Weybridge.

“The Team at APHA have conducted detailed analyses of the virus samples taken from the wildlife,” Dr. Sarah Pitt, microbiologist and principal lecturer at the University of Brighton, who was not involved in the research, said. “It shows that some birds in that region can be infected with avian influenza. However it is worth noting that there is no evidence for the presence of the virus in some of the species of bird investigated.” Falchieri and team also collected samples from albatross and giant petrol colonies on Bird Island, which tested negative for HPAI H5N1.

“The report suggests that only dead seals were tested, so the extent of the problem in the seal population is not known (so it is a qualitative result, showing that seals can be infected and affected by the virus),” Pitt added. The statement released by the APHA does not discuss whether HPAI H5N1 was the cause of death for the tested mammals.

How did the mammals become infected?

Sequence analysis from infected birds suggests that the virus has most likely been introduced through migratory bird movement from South America, the APHA report said. The genomic surveillance data also does not provide any evidence for a widespread mammalian adaptation of the virus.

“Finding HPAI in several individuals of the same species of mammal does not necessarily mean that the virus has been spreading between individuals within that species,” said Dr. Alastair Ward, associate professor of biodiversity and ecosystem management at the University of Leeds, who was not involved in the research.

Ward continued, “It seems feasible that mammals, such as seals, that are known to scavenge, may become infected when they consume infected bird carcasses.”

Is there an increased risk to humans?

The APHA’s statement emphasized that the risk of human infection with H5N1 remains very low.

“Very specific changes are needed within the virus’s genome that make it better adapted to a human host; these changes have not been detected in samples taken from wild birds or mammals to date, so the risk to humans likely remains low,” Ward said. “Nevertheless, these viruses are highly adaptable, so it would be wise to maintain surveillance programs so that we can detect new variants as they emerge and hence respond appropriately in good time if it becomes necessary to do so.”

The appearance of HPAI H5N1 in birds and mammals in South Georgia is saddening, said Professor Ian Brown, APHA’s director of scientific services: “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. If avian influenza continues to spread throughout the sub-Antarctic region, this could significantly threaten the fragile ecosystem, and potentially put a number of very large populations of seabirds and sea mammals at risk.”

“APHA will continue to work with the Government of South Georgia and South Sandwich Islands, the Falkland Islands and the British Antarctic Survey to monitor the impact on the wildlife on South Georgia, and the potential spread to other areas,” Brown concluded