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 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.

Nevada has confirmed its first human case of bird flu in a farm worker who was exposed to infected dairy cattle, the Central Nevada Health District said on Monday, after authorities last week reported a second strain of the virus in cows in the state.