Dairy cows in Nevada have been infected with a new strain of bird flu virus different from the one circulating in other herds throughout the past year, the U.S. Department of Agriculture (USDA)

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.

The USDA said four Nevada dairy herds were infected with an H5N1 bird flu strain that has circulated in wild birds, making prospects for containment in cows appear dim.