NewsBird flu is infecting more mammals. What does that mean for us?

Bird flu is infecting more mammals. What does that mean for us?

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H5N1, one of the many viruses that cause bird flu, had already killed at least 24,000 South American sea lions along the continent’s coasts in less than a year. Now it had come for elephant seals.

Young chickens at a farm in Pescadero, Calif.
Young chickens at a farm in Pescadero, Calif., on Feb. 29, 2024. Rachel Bujalski/The New York Times

By Apoorva Mandavilli and Emily Anthes, New York Times Service

April 22, 2024 | 9:43 AM

In her three decades of working with elephant seals, Dr. Marcela Uhart had never seen anything like the scene on the beaches of Argentina’s Valdés Peninsula last October.

It was peak breeding season; the beach should have been teeming with harems of fertile females and enormous males battling one another for dominance. Instead, it was “just carcass upon carcass upon carcass,” recalled Uhart, who directs the Latin American wildlife health program at the University of California, Davis.

H5N1, one of the many viruses that cause bird flu, had already killed at least 24,000 South American sea lions along the continent’s coasts in less than a year. Now it had come for elephant seals.

Pups of all ages, from newborns to the fully weaned, lay dead or dying at the high-tide line. Sick pups lay listless, foam oozing from their mouths and noses.

Uhart called it “an image from hell.”

In the weeks that followed, she and a colleague — protected head to toe with gloves, gowns and masks, and periodically dousing themselves with bleach — carefully documented the devastation. Team members stood atop the nearby cliffs, assessing the toll with drones.

What they found was staggering: The virus had killed an estimated 17,400 seal pups, more than 95% of the colony’s young animals.

Dead elephant seals line the beach at Punta Delgada, Chubut, Argentina.Dead elephant seals line the beach at Punta Delgada, Chubut, Argentina, on Oct. 10, 2023. – Ralph Vanstreels/UC Davis via AP

The catastrophe was the latest in a bird flu epidemic that has whipped around the world since 2020, prompting authorities on multiple continents to kill poultry and other birds by the millions. In the United States alone, more than 90 million birds have been culled in a futile attempt to deter the virus.

There has been no stopping H5N1. Avian flu viruses tend to be picky about their hosts, typically sticking to one kind of wild bird. But this one has rapidly infiltrated an astonishingly wide array of birds and animals, from squirrels and skunks to bottlenose dolphins, polar bears and, most recently, dairy cows.

“In my flu career, we have not seen a virus that expands its host range quite like this,” said Troy Sutton, a virologist who studies avian and human influenza viruses at Penn State University.

The blow to sea mammals, and to dairy and poultry industries, is worrying enough. But a bigger concern, experts said, is what these developments portend: The virus is adapting to mammals, edging closer to spreading among people.

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