We've all heard of the influenza virus. We've all probably even heard of the H5N1 virus (i.e. the bird flu virus). Not only are they highly contagious and dangerous, but they caused, and can still cause, widespread epidemics. They are scary. Indeed, they’re the reason people line up to get vaccinated as soon as rumors of a flu outbreak start. They’re also why people instinctively take a step back when someone nearby starts coughing.