New evidence shows that bird flu, or avian influenza, is mutating beyond chickens and cows. A Nevada dairy worker tested positive for the new variant of the disease.

The newer strain had been seen before in more than a dozen people exposed to poultry, but this is the first time an infection was traced to a cow.

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.