The new strain, D1.1, is different from the strain, B3.13, that has been detected in other dairy herds throughout the country, but has been connected to serious infections in humans.

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.

That's the way one scientist puts it — referring to how infected wild birds survive long enough to spread it to birds and mammals around the world. And that's a serious risk for human health.