TED-Ed explains the science of how viruses can jump from one species to another and the deadly epidemics that can result from these pathogens.

Here’s a story that happened right here in Maryland.

At a Maryland country fair in 2017, farmers reported feverish hogs with inflamed eyes and running snouts. While farmers worried about the pigs, the department of health was concerned about a group of sick fairgoers. Soon, 40 of these attendees would be diagnosed with swine flu. How can pathogens from one species infect another, and what makes this jump so dangerous? Ben Longdon explains.