A pig on an Oregon farm tested positive for bird flu for the first time in the U.S. on Oct. 30, concerning virologists because pigs have been a source of prior human pandemics. The USDA said on Nov. 6 that a second pig on the farm had also tested positive.

On a recent Monday morning, workers began their week on a large poultry farm in Franklin County, Washington, home to over 800,000 chickens. By the end of the day, avian flu had been discovered among some of those chickens.

The general public health threat remains low, but some infectious disease experts worry about a thinning line that's kept bird flu from spreading between people.

H5N1 bird flu is spreading among animals and humans, raising concerns about mutation risks. While human cases are mild, experts stress urgent preparedness for potential pandemics and vaccine readiness gaps.