Seal pup die-off from avian flu in Argentina looks ‘apocalyptic’

A very contagious strain of highly pathogenic avian influenza (HPAI) is wreaking havoc on elephant seals (Mirounga leonina) on the coast of Patagonia, Argentina. According to the Wildlife Conservation Society (WCS), almost 96 percent of elephant seal pups living at three breeding sites where the H5N1 strain of HPAI was detected have died. The WCS team estimates 17,000 elephant seal pups died in these areas in 2023.

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“It’s the first report of massive elephant seal mortality in the area from any cause in the last half century. The sight of elephant seals found dead or dying along the breeding beaches can only be described as apocalyptic,” WCS Executive Director of Health Chris Walzer said in a statement. “This 2023 die-off contrasts starkly with the 18,000 pups born and successfully weaned in 2022.”

The WCS believes that the elephant seals had little to no interaction with infected bird populations, which is further evidence of mammal to mammal transmission. According to veterinarian Marcela Uhart at the University of California, Davis, since newborn elephant seal pups suckle their mothers to feed, there is little chance that the pups ate infected birds. “This is all highly suggestive of some sort of transmission between mammals,” Uhart told New Scientist.

A recently deceased elephant seal pup. The pup was probably a week old when it died. CREDIT: ©Maxi Jonas.

H5N1 was first detected in 1996 in China. The virus had been largely confined to domesticated birds for several years, but has been spreading quickly in wild populations since 2021. H5N1 infected over 150 domestic and wild bird species around the world. Over 500,000 birds in South America alone have died from the disease. H5N1 has also killed more than 2,200 Dalmatian pelicans in Greece and about 20,000 Sandwich terns in the Netherlands.

Bird flu spreads through air droplets and bird feces. According to WCS, it is exacerbated by alterations to bird migration schedules due to human-caused climate change and repeated re-circulation in domestic poultry. There have also been outbreaks of the virus at mink farms in France and Spain and the USDA banned poultry imports from France in October 2023. Scientists confirmed that the virus jumped to wild mammals in May 2022 and has since been detected in dozens of mammals including pumas, foxes, skunks, and brown bears. Roughly 700 endangered Caspian seals died from the virus in 2023. H5N1 also killed a polar bear for the first time in fall 2023, according to health officials in Alaska.

[Related: USDA bans French poultry imports over avian influenza vaccine.]

In response to the spread, the World Health Organization has urged public health officials to prepare for a potential spillover to humans. Initially, scientists thought that mammals could only catch the virus through contact with infected birds. While cases of humans getting infected and seriously ill from bird flu are rare, the more it spreads among mammals, the easier it will be for the virus to evolve to transmit more easily between them. For COVID-19, the number of healthy humans infected by a single sick individual–or R naught value–initially ranged from 1.7 to 7 new infections. Among birds with H5N1, around 100 birds can be infected by a single sick bird.

“It is imperative that we take a collaborative One Health approach to identifying emerging strains of bird flu across the globe to support the development of specific and universal vaccines that can quickly treat infection in people to prevent another pandemic,” said Walzer. “The cost of inaction is already causing major devastation to wildlife. As we work to help affected populations recover, we must remain vigilant against the spread of this deadly pathogen to people before it’s too late.”