Viruses work by taking control of our cells and carefully reprogramming them into machines to make more viruses. Because of this, a virus infecting a new host species is like someone trying to win an argument by shouting at people in a language that they can’t understand. And this is where pigs come in.

Pigs can become coinfected with bird and human viruses, allowing genes to swap to form a new, more dangerous virus that can more easily infect humans.

Another cause for concern: flu season is underway in the U.S., and as seasonal influenza virus goes around, “humans, ourselves, could be a mixing vessel,” Davis says. If a person were simultaneously infected with bird flu and seasonal flu, the two viruses could theoretically combine to create a more transmissible strain.

The United States Department of Agriculture last week reported that a pig on a backyard farm in Oregon was infected with bird flu.

H5N1 avian flu was confirmed in a pig on a backyard farm in Oregon, the first detection of the virus in hogs in the