A dairy worker in Nevada has been confirmed to be infected by a new bird flu strain found to be spreading among cows in the state last week . That strain of the H5N1 bird flu virus, called D1.1 by scientists, is different from a previous variant called B3.13 which had infected at least 40 dairy workers in the U.S. to date.

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.