A newer variant of H5N1 bird flu that recently infected dairy cattle in Nevada has a genetic change thought to help the virus infect mammals – including humans – more easily, according to a new brief from the USDA’s Animal and Plant Health Inspection Service.

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.