Dairy herds in Nevada have been infected by a version of the H5N1 bird flu not previously seen in cows, putting virologists on high alert.

Until last week, all bird flu in dairy herds had been identified as the B3.13 variant, which was believed to have come from wild birds in late 2023 or early 2024. The USDA confirmed the virus's existence in the Nevada dairy cattle through milk sampling, the agency said.