A strain of bird flu spreading among dairy cows in Nevada has infected a dairy worker in the state, the Centers for Disease Control and Prevention said Monday.

The newer strain had been seen before in more than a dozen people exposed to poultry, but this is the first time an infection was traced to a cow. The Nevada dairy worker was exposed at a farm in Churchill County, in the west central part of the state, state health officials said.

The variant of bird flu that killed a Louisiana resident has now been found in dairy cows. Until now, the human cases of bird flu traced to cattle have been mild, mostly eye infections. But the U.S. Department of Agriculture confirmed that a strain previously found only in wild birds has turned up in dairy herds in Nevada ‒ raising concerns that future human infections could be more serious.