Six dairy herds in Nevada have tested positive for a newer variant of the H5N1 bird flu virus that’s been associated with severe infections in humans, according to the Nevada Department of Agriculture.

In the US state of Nevada, a newly identified H5N1 bird flu strain, D1.1, has been found in six dairy herds. Scientists warn the virus could become endemic, posing risks to livestock and human health.

The strain of bird flu is distinct from what has previously been found in dairy cattle. The finding means the virus has again spilled over from birds to cows, and it raises some worrying questions.