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.

An emerging strain of highly pathogenic avian influenza has spilled over from wild birds to dairy cows in the state of Nevada, and officials at the US Department of Agriculture (USDA) and some scientists are concerned by a mutation they are seeing.

Experts said it raises new questions about wider spread and the difficulty of controlling infections in animals and the people who work closely with them.