WASHINGTON, D.C., December 19, 2025 On December 14, 2025, USDA’s Animal and Plant Health Inspection Service (APHIS) announced the first detection of highly pathogenic avian influenza (HPAI) in a dairy herd in Wisconsin . On December 17 , the National Veterinary Services Laboratories (NVSL) completed whole genome sequencing and confirmed that the virus is H5N1 clade 2.3.4.4b genotype D1.1. Analysis indicates that this detection is a new spillover event from wildlife into dairy cattle, separate from previous events. Key Points -- Most detections in U.S. dairy herds have resulted from movements linked to the original spillover event that occurred in the Texas Panhandle in late 2023, involving the B3.13 strain . -- In early 2025, through the National Milk Testing Strategy , USDA detected two spillover events in Nevada and Arizona dairy herds. Both were identified early, and no further herd infections occurred through animal movements. These events involved the D1.1 strain...