Why scientists are worried about the latest transmission of bird flu to cows

William Brangham:

In fact, unlike cows, this avian flu has been fatal to nearly two dozen other infected mammal species in the United States, from polar bears in Alaska to mountain lions in Colorado to raccoons. and foxes. Many of these animals were likely infected by eating dead animals carrying the virus.

But, by far, the biggest impact here in the United States has been on birds. Since this strain of avian flu arrived in the United States in early 2022, brought here by migratory birds, more than 90 million domestic birds, mostly chickens and turkeys, have died or been intentionally killed in 48 states.

And unlike previous outbreaks, this variant affected more wild birds and spread over a wider geographic area, reaching South America in late 2022.

Dr. Ralph Vanstreels, University of California, Davis: I think the alarm really went off when it reached Peru, and this is a huge seabird community, and we saw mortality unprecedented among seabirds there.