Thin-section transmission electron micrograph, TEM, of a single measles virus particle or virion Kallista ImagesGetty Images Measles is back, and its been tearing through the country from California to 13 other states. Already, the number of cases has broken 100. But how is it spreading so fast, and why is it so contagious?Roberto Cattaneo, PhD, is the scientist credited with figuring that out. A professor...