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.

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

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

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.

California declared a state of emergency this week over the spread of bird flu in the state as the virus continues to be detected among the state’s cattle herds. California Gov. Gavin Newsom (D) said in a statement Wednesday that the declaration of an emergency is meant to “ensure government agencies have the resources

Bird flu, or avian influenza, is a rare but serious disease that can spread from birds to humans under certain conditions. So far, most cases have been confirmed through direct contact with infected birds or other animals,

More than 4 million chickens and turkeys have been killed across California in an attempt to stop the virus from spreading.

At least 61 people in the US have contracted bird flu amid outbreaks in poultry and dairy cows. What are the symptoms? What to know about highly pathogenic avian influenza, aka, H5N1.