Since H5N1 avian influenza made the unexpected jump from birds to cattle, experts are increasingly worried about human spread.Rodrigo Abd/AP PhotoGov. Gavin Newsom of California declared a "proactive" state of emergency over the H5N1 bird flu.The virus has spread rapidly through US dairy cattle herds, with 16 states affected.The CDC reports low public risk with no human-to-human spread, but 61 human cases have been detected.Gov.