The first severe case of H5N1 bird flu was confirmed in Louisiana. Here is a map of other states that have been affected.

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 virus, which has spread for years in wild birds, commercial poultry and many mammal species.

Gov. Gavin Newsom declared a state of emergency Wednesday as the H5N1 bird flu virus moved from the Central Valley to Southern California dairy herds, while federal officials confirmed the first U.S.