Mississippi state and federal officials have confirmed an outbreak of a strain of bird flu not reported in the U.S. since 2017, with quarantine and depopulation efforts already underway.

When biologists first noticed increased bird flu cases in October, 49 cases had been reported. But because they can only test a limited number of carcasses, the true number is likely higher.

According to the governor's office, more than half of all avian flu cases in the United States are in Pennsylvania.

After a catastrophic outbreak of bird flu devastated southern elephant seal populations in 2023, scientists are on high alert.

The confirmation last week of H5N1 bird flu in northern elephant seals at California’s Año Nuevo State Parkhas put wildlife managers and public health officials on alert.