By Leah Douglas and Tom Polansek CHICAGO (Reuters) -H5N1 bird flu was detected in a pig in a backyard farm in Oregon, the first detection of the virus in swine in the country, the U.S. Department of Agriculture said on Wednesday.

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.

H5N1 avian influenza, more commonly known as bird flu, has infected more than 100 million birds in the U.S. and almost 500 dairy cattle herds across 15 states. The virus has popped up in mammals including elephant seals,