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.

The new H5N1 version, known as D1.1, was found in dairy cattle in Nevada and is different than the B3.13 type that has spread to more than 950 herds in 16 states over the past year, starting in Texas. The D1.1 infection was discovered by testing raw milk under a USDA dairy surveillance project launched last year.