The avian influenza virus adapted to marine mammals. This may not be done yet.

In South America, elephant seals died in large numbers because the avian flu virus acquired mutations that allowed it to spread among mammals, a new study suggests.

The research provides the first genetic and epidemiological evidence of transmission of the avian influenza virus between mammals. And the findings contain a warning: The virus, called H5N1, could similarly mutate to cause large-scale infections in other mammal species, including humans.

The avian flu virus is responsible for an ongoing outbreak among dairy cows in the United States. Since March, it has been detected in cows in 11 states and in wastewater in several others.

The virus may already be spreading from cow to cow, but federal officials have said the most likely explanation for the outbreak is that it is spread through contaminated milk.

Infected cows have large amounts of virus in their milk, which may be thick and yellowish. Some cows were slaughtered because they never returned to normal milk production, and others died from secondary infectionsaccording to a Reuters report.

H5N1 is also believed to have spread among minks on a fur farm in Spain. But the new study is the first to bring together different streams of evidence confirming transmission from one mammal to another.

The study was put online Saturday and has not been peer-reviewed. But genetic analysis of the virus, as well as the scale and timing of infections in South American marine mammals, all suggest that the animals contracted the virus from each other, not from infected birds. indicated the researchers.

“It’s a combination of facts that present compelling evidence that there is some sort of mammal-to-mammal transmission,” said Marcela Uhart, who led the new study and directs the Wildlife Health Program. of Latin America at the University of California, Davis.

In 2022 and 2023, H5N1 killed more than 30,000 sea lions in Peru and Chile, as well as porpoises, dolphins and otters. He traveled along the Pacific coast, then up the Atlantic coast, passing through Argentina, Uruguay and Brazil.

Last October, there was a “virus tsunami” in Argentine Patagonia that wiped out more than 17,000 elephant seals, Dr. Uhart said, adding that these figures make it unlikely that the virus passed through every time. a bird to a marine mammal.

Mammal-to-mammal transmission is “almost the only explanation for how it spread across the entire southern tip of the continent and continued to spread,” she said. “Honestly, there aren’t many other ways this could have happened.”

In the new study, Dr. Uhart and his colleagues studied virus samples from baby elephant seals and terns. Their genetic analysis suggests that H5N1 jumped from wild birds to marine mammals on the Pacific coast of South America at least three times, then evolved to spread among elephant seals.

The team presented some of this data in small meetings, but other researchers were reluctant to accept the idea that marine mammals were infecting…

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