A second subtype of H5 bird flu, known as D1.1, was detected in dairy cattle and infected one worker in the US state of Nevada. On February 10, 2025, the US Centers for Disease Control and Prevention released data showing the new D1.

When it comes to the potential of H5N1 avian flu, otherwise known as bird flu, picking up mutations that may lead to human-to-human spread, that "train has already left the station," warns one infectious disease expert.

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.

Dairy herds in Nevada have been infected by a version of the H5N1 bird flu not previously seen in cows, putting virologists on high alert.

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,

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.