A dairy worker in Nevada has reportedly been infected by the killer variant of H5N1 bird flu; analysis shows changes in new strain that makes it more lethal in mammals.

The newer variant of avian influenza that recently infected dairy cattle in Nevada has a genetic change that’s thought to help the virus copy itself in mammals — including humans — more easily, according to a new technical brief from the US Department of Agriculture’s Animal and Plant Health Inspection Service.

Cows in Nevada have been infected with a strain of H5N1 bird flu different from the strain detected in all other herds to this point in the ongoing dairy outbreak. It's the same strain that killed a Louisiana resident in early January and sent a Canadian teenager to intensive care in early November.

A version of the H5N1 virus that has killed one person and severely sickened another has been detected in milk samples collected from Nevada dairy herds.

The USDA said four Nevada dairy herds were infected with an H5N1 bird flu strain that has circulated in wild birds, making prospects for containment in cows appear dim.

Nevada dairy cattle infected with a new bird flu strain, Type A H5N1 D1.1, raising concerns of multiple transmission channels.

Dairy cows in Nevada have been infected with a new strain of bird flu virus different from the one circulating in other herds throughout the past year, the U.S. Department of Agriculture (USDA)

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.