A paper in Nature communications in September 2024 reports on the detection H5N1 high pathogenicity avian influenza virus (HPAIV) in the Antarctic, where HPAIV had “never previously been detected”. After initial detection in brown skuas at Bird Island, South Georgia, in October 2023, H5N1 HPAIV was confirmed across several sampling locations in multiple avian species and two seal species. It was also confirmed in southern fulmar and black-browed albatross in the Falkland Islands. The article describes the detection, species impact, and genetic composition of the virus, proposing introductory routes and potential long-term effects on avian and mammalian species in the region.
HPAIV in the Antarctic region
The Antarctic region comprises the ice shelves, water, and island territories in the Southern Ocean inside the ‘Antarctic Convergence’ or ‘Antarctic Polar Front’, a marine belt where Antarctic waters meet the warmer sub-Antarctic waters. HPAIV had not previously been reported inside the region, which hosts “unique ecosystems which support the population strongholds of several avian and marine mammal species”. Although the “relative isolation” of the islands from human populations offers some protection from “anthropogenic environmental change”, wildlife populations in the Antarctic face varied challenges, from introduced species to longline fisheries and rapid climate change.
Several native bird species are listed as vulnerable or endangered. Iconic long-lived species with late maturity exhibit “low resilience to rapid increases in population mortality”. Thus, high mortality disease outbreaks represent a “substantial threat to already vulnerable seabird populations”. Several seabird species range between the South Atlantic and Southern Ocean, heading to the South American coast to forage or overwinter.
Birds like brown skuas, kelp gulls, southern giant petrel, and snowy sheathbills are known to be potential vectors of infectious pathogens to the ecosystem because of the migratory traits, scavenging behaviour, and acknowledged roles as carriers of low pathogenicity avian influenza viruses (LPAIV).
Detection of H5N1
The authors report the discovery of a southern giant petrel “showing behaviours indicative of loss of coordination, neurological twitching, and lethargy” by researchers of the British Antarctic Survey (BAS) on Bird Island, South Georgia, on 17th September 2023. The bird was observed being preyed and scavenged upon by brown skuas and other southern giant petrels. On 8th October, brown skuas in the same area were found showing lethargy, neck spasms, twitching, and an inability to fly. By 10th October, bird mortality was seen on Bird Island; highest mortality occurred at the roosting site of non-breeding birds. Swab samples, taken from three brown skuas on 8th October and a further brown skua on 11th October, yielded PCR positivity for HPAIV H5N1. The birds were later found dead.
More positive samples were identified throughout October and November; by 17th November 57 skuas were observed to have died at Bird Island. On 27th November, a South Georgia shag tested positive from King Edward Cove, and an Antarctic tern sampled dead on 6th December. In early December, clinical disease consistent with mammalian infection with HPAIV was observed in colonies of southern elephant seal and Antarctic fur seal. Clinical presentation included difficulty breathing and individuals showed accumulation of viscous fluid around the nasal fluid. Five southern elephant seals and one Antarctic fur seal samples were collected on 9th December, testing positive for the virus.
Between the initial detection on 8th October and 9th December, 33 avian carcasses and 17 mammalian carcasses were sampled; these included representatives of five avian species and two mammalian species from eight different locations. 66% tested positive for HPAIV H5N1.
On 30th October, a southern fulmar was reported dead on Stanley, Falkland Islands, and tested positive for the virus. Swabs were taken from various avian species across the Falkland Islands, but only three black-browed albatrosses tested positive from Saunders Island (1) and Steeple Jason (2). Between 30th October and 10th December, samples were taken and tested from 13 carcasses from nine different bird species. 31% tested positive for HPAIV H5N1.
The importance of data sharing
“Both the Falkland Islands archipelago and South Georgia represent key areas that are host to significant avian biodiversity and the presence of HPAIV on these islands represents a significant risk to the susceptible bird populations.”
South Georgia, home to around 29 avian species that breed on the island, is a recognised “Important Bird Area”. Any colony or population threatened by an outbreak of HPAIV on the island could affect the wider population of seabirds. Although seabird colonies show space partitioning between colonies, a “high degree of species overlap” is observed, often attributed to the movement of nonbreeders or juvenile birds. Interactions would aid the spread of disease.
Further potential for spread arises from “interlinkages between avian and mammalian species” testing positive for H5N1. Circumpolar and trans-Pacific migrants, like the grey-headed albatross and southern giant petrels, may facilitate this spread. Indeed, a threat of transmission to New Zealand and Australia is inferred from phylogeographic analysis that revealed a dynamic geneflow between southern Atlantic populations and Macquarie Island.
A key element in the “cycle of risk” is the opportunity for infection of scavenging birds, exacerbated by the impossibility of carcass removal, disposal, and environmental clean-up. The region is “one of the most remote environments on earth”, and the potential for virus survival in the cold environment is increased. Furthermore, local ecology of species could “influence the scale of impact”.
“Critically, assessment of sequences derived from mammalian species did not indicate any adaptive mutations of increased risk to human populations.”
The authors emphasise that their data does not indicate any increased risk of infection from the viruses. While there were no mutations that would affect the susceptibility to antivirals, they highlight the need for “continual monitoring”. This is particularly pertinent where the virus appears to be the causative agent of mortality events in seals or other avian species where scavenging occurs.
“Clearly, with continual infection events occurring in mammals globally it is of great importance to understand where mutations may represent a genuine zoonotic risk as well as understand where adaptations that have occurred in mammals become tolerated in avian species.”
The paper concludes that the current impact is “relatively minimal” for avian species. Despite observations of infection and significant mortality events in fur and elephant seals, the authors find no evidence of viral adaptation for enhanced infection of mammals. Thus, they do not predict an increased risk to human populations on the islands. However, the global release of data “restricts a fulsome interpretation”. With limited numbers of sequences available in public databases, interpretation is limited.
“This factor, as with countless other studies, highlights the importance of real-time global data sharing as a key tool in understanding the emergence and spread of these viruses. The current lack of publicly available data precludes a conclusive assessment of potential incursion routes.”
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