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.

A fast-growing outbreak of avian flu has upended California’s dairy industry, the nation’s largest producer of milk, infecting most of the state’s herds and putting thousands of farmworkers at risk for contracting the virus.

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