In the relatively few U.S. cases of human bird flu so far recorded, symptoms have typically been mild -- congestion, pink eye and other transitory effects. But if H5N1 mutated so that it could pass easily between people, "all of this may change," Chin-Hong said.

Bird flu hits Nevada as its effects remain visible at grocery stores. Susanne Rust hated to say it, but she did: “I think the H5N1 bird flu outbreak is going to continue to pest

The detection indicates that distinct forms of the virus known as Type A H5N1 have spilled over from wild birds into cattle at least twice. 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.

State officials say the highly pathogenic avian influenza – more commonly known as bird flu – is widespread in much of the state.