Infectious disease epidemiologists are concerned about the spread of a highly pathogenic avian flu, known as H5N1. It’s already devastated bird populations around the globe. In October, it appeared to be spread mammal-to-mammal on a mink farm in Spain. Marco Werman gets the latest on the H5N1 bird flu in a conversation with William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center in Nashville. He’s also medical director of the National Foundation for Infectious Diseases.