evidence: The recent spread of avian influenza in dairy cattle in the U.S. has startled even some scientists who've tracked a global outbreak of the virus over the last few years. [...] The first cases of this H5N1 bird flu strain emerged in North America among wild migratory birds in late 2021 and soon spread to poultry farms. It's now showing up among dairy cows and at a major egg producer and one person who had close contact with cows has been infected. [...] Currently it's not clear exactly how bird flu is spreading among mammals, and to what extent infections are mostly happening after some kind of contact with infected birds.