A powerful strain of the avian flu has swept through seal colonies in southern Argentina, wiping out many juveniles and raising concern about a spread to other species.

The flu, also known as H5N1, appeared in South America in 2022 and made its way to Patagonian Argentina by August 2023, resulting in extreme mortality among newborn elephant seals. This year, environmental groups are rushing to learn more about the disease and what can be done to prevent it from spreading to other parts of the ecosystem.

“There’s no precedent for a mortality from a highly pathogenic avian influenza like this [in Patagonia],” said Julieta Campagna, who runs coastal protected area monitoring for the NGO Wildlife Conservation Society (WCS) Argentina. “When we first started recording cases, it was mostly seals. Then we started to worry what would happen to other species.”

Cases were first detected in South American terns (Sterna hirundinacea) before moving onto sea lions (Otaria flavescens), fur seals (Arctocephalus australis) and southern elephant seals (Mirounga leonina). H5N1 is present in the provinces of Tierra del Fuego, Santa Cruz, Buenos Aires, Rio Negro and Chubut, according to Argentina’s National Food Safety and Quality Service. Many scientists were surprised that the disease jumped from birds to mammals, especially since seals don’t feed on terns.

Elephant seals were hit the hardest. On the Valdés Peninsula in Chubut, the mortality rate of newborn elephant seals was believed to be as high as 96% last year, compared to 1% or less in 2022, according to a WCS report. A study published in the journal Marine Mammal Science in December and coauthored by Campagna estimated that 17,400 of the 18,000 elephant seal pups born last year died from Avian flu on the coasts of Chubut.

Some adult seals were affected, as well. On one high-density part of the coast, 10 adult males and 36 females were found dead, whereas in previous years even one adult carcass was considered a “rare” event, according to the study.

Especially concerning is the death of young female seals, Campagna said. Without them, reproduction rates could be low again this year — and possibly for years to come.

“We don’t know what’s going to happen to the population,” she said. “For the elephant seal, with the decline that it had last year, with a season where there were basically no calves, that’s going to have an impact on the ecosystem in the long run.”

Because the disease appears to be mutating quickly, scientists are also concerned about a second wave this year, as well as the possibility that it could jump to still more species. Orcas (Orcinus orca) seem like a likely candidate, Campagna said, because they feed on seals. Humans could also catch it if tourists crowd beaches and get too close to sick animals.

Right now, there aren’t any confirmed cases in whales or humans in Argentina, according to Valeria Falabella, the director of coastal-marine conservation at WCS. But there are human cases in other parts of the world, including Chile.

When animals contract avian flu, there isn’t much people can do except close the beach and leave them alone, Campagna said. There are no vaccines or medications. But WCS and other organizations — including the University of California, Davis — are analyzing samples taken during the worst of the outbreak to better understand how it mutated and spread in hopes of identifying new waves of infection.

They’re also in communication with researchers in Chile, Peru, Brazil and Uruguay, where similar cases have been recorded, to understand the different mutations in the region. Until that happens, the most they can do is monitor population trends and hope for the best.

“We have to keep monitoring the populations affected by this epidemic,” Campagna said. “It’s the only way to understand their ability to recover or not.”

Citation:

Campagna, C., Uhart, M., Falabella, V., Campagna, J., Zavattieri, V., Vanstreels, R. E., & Lewis, M. N. (2023). Catastrophic mortality of southern elephant seals caused by H5N1 avian influenza. Marine Mammal Science, 40(1), 322-325. doi:10.1111/mms.13101

Banner image: Dead elephant seals on a beach in Argentina. (Photo by Maxi Jonas/WCS)

Editor’s Note: The article previously said the flu arrived to South America in early 2023; it actually arrived in 2022.

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