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.