A new H5N1 bird flu mutation has appeared in a cluster of infected dairy cows. It's a genetic change that scientists say could not only make the virus more lethal, but increase its spread between mammals and possibly humans.

The ongoing bird flu outbreak has led to wild bird deaths, slaughtered livestock, and hazardous conditions for dairy industry workers.

No new human cases of avian influenza have been reported, and poultry infections are low so far in March. But infections in cats are continuing, and new research is raising concerns about the virus