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.

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.

Officials have discovered the virus in 645 dairy herds, more than in any other state so far. In a stark acknowledgment of the increasing seriousness of bird flu’s spread, Gov. Gavin Newsom of California declared on Wednesday that the outbreak of infections among the state’s dairy cattle constituted an emergency.

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. That raises new questions about the outbreak of the virus,

CDC and NIAID Los Angeles County health officials reported the first human case of bird flu in the area less than a week after a statewide emergency declaration was announced. In a statement released on Monday,