Bird Flu Is Infecting More Mammals. What Does That Mean for Us?

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.

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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.

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 The U.S. is prepared for an influenza pandemic, with some stockpiled vaccines and antivirals, but its efforts at monitoring the virus may not pick it up quickly enough to deploy those tools.

It took several weeks before farmers, and then officials, knew that H5N1 was circulating in dairy cows.

The dairy farm outbreak has resulted in only one mild human infection, but farms are fertile ground for the virus to jump species — from cat to cow to pig and human, in any order.

Many scientists worry in particular about pigs, which are susceptible to both human and avian flu strains, providing the perfect mixing bowl for viruses to swap genes. Pigs are slaughtered when very young, and newer generations, with no prior exposure to flu, are particularly vulnerable to infections.

So far, H5N1 does not seem adept at infecting pigs, but that could change as it acquires new mutations.

Bird Flu Is Infecting More Mammals. What Does That Mean for Us? - The New York Times (nytimes.com)