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Viruses love to jump between animal species.

In 2023K a highly pathogenic bird flu leapt to seals in South America, killing some 17,000 elephant seal pups (about 97 percent of the vulnerable animals) and an unknown number of adults in a major breeding colony in Península Valdés, Argentina. A new genetic analysis, published in the science journal Nature Communications, determined that once the virus entered this population of marine mammals, it evolved and spread easily between seals, likely stoking a transnational outbreak.

The results underscore the risk of bird flu spread in animals, including us. After all, some 75 percent of emerging infectious diseases in humans come from other animal species. These are known as zoonotic diseases.

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"We reflect that H5N1 viruses becoming more evolutionary flexible and adapting to mammals in new ways could have global consequences for wildlife, humans, and/or livestock," the scientists wrote.

FYI: The images below show dead seals and birds.

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SEE ALSO: These animals went extinct in 2023

The dramatic, recent consequences for the elephant seals of Península Valdés can be seen in the images below.

"We were totally appalled by the dramatic impact of the epidemic of avian influenza on this population," Valeria Falabella, a study coauthor and the director of coastal and marine conservation at Wildlife Conservation Society Argentina, said in a statement. "It is likely that more than half of the reproductive population died due to the virus. It will take decades before the numbers are back to the 2022 population size."

Before the seals died, researchers observed telltale signs of infection in the pups, including labored breathing, tremors, trouble moving, and nasal discharge.

The carcasses of elephant seal pups documented in Punta Delgada, Argentina, in October 2023. Credit: Marcela Uhart / UC Davis An August 2024 image of skeletal remains of elephant seal pups from the Península Valdés colony. The outbreak occurred in 2023. Credit: Marcela Uhart / UC Davis In foreground: the remains of a dead elephant seal pup in Península Valdés. In background: young elephant seals on the beach. Credit: Ralph Vanstreels / UC Davis Dead elephant seal pups seen on the beach in Punta Delgada, Argentina, in October 2023. Credit: Ralph Vanstreels / UC Davis

Swabbed samples taken from infected seals showed how the H5N1 virus has become increasingly adaptable to new hosts. The viruses found in seals and birds (such as terns) in Argentina formed a distinct clade or group that also spread to seals in Peru, Chile, Brazil, and Uruguay.

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This virus isn't going away. While it hasn't been detected in the decimated elephant seal colonies in 2024, it has been "widespread in wild birds and has caused outbreaks in poultry and U.S. dairy cows, with recent cases reported among dairy and poultry workers," UC Davis, whose researchers worked on the new study, explained. Fortunately, the virus isn't spreading from humans to other humans — though it is infecting some U.S. dairy and poultry workers (46 people have been reported infected in the U.S. as of Nov. 11, according to the CDC).

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The researchers will continue monitoring the spread of this virus in the wild and elsewhere, with the aim of understanding how it's evolving.

It's unknown, of course, when or where the next novel viral outbreak in humans will come from. It could be a long time. Or not. It could be another coronavirus. Or another influenza virus — which caused the devastating 1918 flu pandemic (and may have started as an avian flu). But what's certain, although sometimes easy to forget, is that our history is punctuated by pandemics.

Topics Health

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