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. The virus, also known as Type A H5N1, was detected for the first time in U.S. dairy cattle in March. Since then, bird flu has been confirmed in at least 866 herds in 16 states. More than 60 people in eight states have been infected, with mostly mild illnesses, according to the U.S. Centers for Disease Control and Prevention. One person in Louisiana has been hospitalized with the nation’s first known severe illness caused by the virus, health officials said this week….