Pigs can be mixing vessels for bird flu and human flu viruses.Charity Burggraaf/Getty ImagesA pig has tested positive for H5N1 bird flu in a backyard farm in Oregon.Pigs can host both bird and human flu viruses, which can make them a dangerous "mixing bowl."Flu season can also heighten the risk of mutations and eventual human transmission of H5N1.A bird flu virus has jumped one species closer to a human outbreak.The H5N1 bird flu was detected in a pig in Oregon, the first instance of a swine infection in the US, officials announced on Wednesday.Pigs get both bird flu viruses and human flu viruses, making them a genetic mixing bowl where H5N1 could gain genetic mutations that help it spread between humans.That's not inevitable, but "I would say the concern elevated slightly with this pig infection," Stacey Schultz-Cherry, a virus expert at St.