Federal authorities say it is likely being carried from farm to farm on objects like farm equipment or clothing that has touched a sick cow.

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.

The bird flu outbreak has spread to all 50 states, these maps show. Here are the symptoms and what to do if you think you might be infected.

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.

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.