High mortality among young elephant seals on South Georgia | Polarjournal
Southern elephant seals crowd the beaches of South Georgia in their thousands, amidst penguins and with numerous seabirds as neighbors. However, this also brings them into quicker contact with the globally rampant HPAI H5N1 virus, which is now raging among seals. (Photo: Michael Wenger)

The fact that the highly contagious bird flu virus HPAI-H5N1 also affects marine mammals and kills them en masse has been known since the numerous dead seals along the coast of South America. Since October, the virus has now also been detected in the Antarctic, more precisely on South Georgia. There it is spreading rapidly across the island, leaving behind not only dead seabirds, but could also affect elephant seals.

The British Antarctic Survey BAS and the Government of South Georgia and the South Sandwich Islands GSGSSI report numerous dead young elephant seals at several locations on the island. In addition, the observers recorded many animals at other locations that are already showing symptoms of disease, as the BAS reports. How many animals have died so far is still unknown. However, animals affected at seven locations on the island are on the GSGSSI’s site response list. Experts fear that the virus could soon spread to Antarctica and affect the wildlife there.

Young elephant seals are well protected against bad weather and grow to a good size quickly thanks to their high-fat milk so as not to be accidentally killed by bulls or other animals. But the little ones have little protection against a virus. (Photo: Michael Wenger)

Interestingly, the HPAI-H5N1 virus could not be detected in the dead elephant seals, unlike in the dead seals in Uruguay and Argentina. According to the authorities, the virus had led to a high mortality rate in the latter country, particularly among elephant seals. The causes of death of the young elephant seals on South Georgia are currently being investigated. The BAS and the GSGSSI are currently drawing up plans to obtain more samples for more conclusive results. To date, only rod samples have been taken from dead animals and tested for HPAI-H5N1 in Weybridge, UK. According to the BAS, however, these tests were negative and the virus could not be detected.

UPDATE: Dr. Michelle Wille from the University of Melbourne and Professor Ashley Banyard from the British Animal and Plant Health Agency (APHA) in Weybridge explain why the virus has not yet been detected with the following original statement:

First, HPAI infection in mammals is highly neurotropic, and colleagues have remarked that the traditional nasal (which are useful in detecting respiratory infections) and rectal (which are useful in detecting gastrointestinal infections) swabs, are frequently returning false negatives (Postel et al. 2022, Bennison et al. 2023). This, Swab sampling has been shown to not necessarily be sufficient for detection of viral RNA during mammalian infection. Therefore, to detect HPAI infection in mammals, more invasive sampling may well be required, such as collecting a brain sample from carcasses. However, barriers to invasive sampling include lack required highly trained personnel on the ground, lack of suitable respiratory and personal protective equipment, and a lack of appropriate facilities to process the samples. In response, APHA staff have been deployed to South Georgia to evaluate sampling options and help assist teams in the area. It is hoped that a more thorough samples set can be taken to enable either confirmation or exclusion of HPAI in mammals in the near future.

Second, based on the full genomes of HPAI from Brown Skuas and Fulmar in the sub-Antarctic (and marine mammals in South America) which are publicly available on the GISAID (Global Initiative on Sharing All Influenza Data) sequence database, there is no evidence of mutations (single nucleotide polymorphisms – SNPs) in the parts of the virus genome that are used for diagnostics. Further, the diagnostic approach at APHA includes three different test which target by three different regions of the virus genome, including highly conserved regions. Therefore, a trifecta of mutations is not only highly implausible, but there is no evidence for this based on the viral genome data in hand.

While mutations have been detected in mammalian cases globally, we have not yet identified adaptive mutations suggestive of mammal-to-mammal transmission. One key reason for the explosion in mammalian cases is linked to increased environmental pressure from infection in wild birds. Essentially, many locations are like an “all day buffet” for predatory and scavenging mammals which are being infected following the consumption of infected bird carcasses (EFSA 2023). Indeed, the consumption of dead or sick birds has been observed in South American Sea Lions (Gamma-Toledo et al. 2023Second, many marine mammals haul out in areas that are shared by marine birds, and therefore they are exposed to infected guano leading to environmental exposure. Indeed, this has been identified as an important route of transmission to seals in North America (e.g. Lair et al. 2023, Puryear et al. 2023). The large number of marine mammal cases in South America (and South Georgia) has experts worried about the potential of viral mutations allowing for more efficient mammalian transmission, but these features have not clearly been identified in the genome sequences and a substantial amount of work is still required to clarify this point.

The map displays all the landing sites in South Georgia where visits are normally permitted. The colors mark security levels for the HPAI virus according to the GSGSSI biosecurity manual: yellow = level 1 (open, taking into account the increased biosecurity measures); orange = level 2 (closed to tourists), red = level 3 (closed to all until the end of the season) Map status: November 20, 2023. Map: GSGSSI

Since the virus was detected on South Georgia, more precisely on Bird Island, in mid-October, the administration has declared warning levels from 1 to 3 for 33 landing sites that usually are visited by tourists. While warning level 1 still allows visits for everyone and are subject to increased biosecurity measures, tourist visits are no longer permitted from warning level 2 and research work is also prohibited at warning level 3. At the present time, the GSGSSI has declared level 1 for 14 landing sites, level 2 for 16 sites (including Grytviken and King Edward Point) and warning level 3 for 3 landing sites, which means complete closure. The latter includes the well-known landing sites of St. Andrews Bay, the largest colony of king penguins on South Georgia, and Cooper Bay, a gathering place for the popular macaronis.

However, closing Grytviken only restricts tourists from coming ashore. Administrative procedures will continue to take place on board the vessels. Places with a level 2 classification can be upgraded to level 1 again after a thorough review of the situation and the animals, whereas a level 3 classification means closure until the end of the season. Whether they can be reopened the following year depends on a reassessment of the sites by the authorities and expert groups. How the population of elephant seals on South Georgia, which has only slowly recovered from the slaughter by sealers in the 19th century, will fare is still up in the air.

Dr Michael Wenger, PolarJournal

Link to the GSGSSI biosafety website

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