A version of the avian influenza virus different from the one rampaging through herds since last spring has been detected in dairy cows in Nevada, USDA says.

The finding indicates that the virus, known as H5N1, has spilled from birds into cows at least twice — leading to these two sets of infections — and that it could continue to do so. It also suggests that the virus may pose a persistent risk to cows and to the people who work closely with them.

The U.S. Department of Agriculture has detected a bird flu strain in dairy cattle that previously had not been seen in cows, the agency's Animal and Plant Health Inspection Service said on Wednesday.