Gov. Gavin Newsom’s declaration has riled up concern, particularly in other top dairy-producing states, such as Wisconsin and Pennsylvania.

Bird flu virus has swept through farms across the nation’s largest dairy producing state. All human cases had been mild - until now.

California officials have declared a state of emergency over the spread of bird flu, which is tearing through dairy cows in that state and causing sporadic illnesses in people in the U.S.