On Jan. 31, 2025, the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed by whole genome sequence the first detection of highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b, genotype D1.1 in dairy cattle.

The confirmation, a result of a State of Nevada tracing and investigation, followed an initial detection on silo testing under the USDA’s National Milk Testing Strategy in Nevada. The sequencing was conducted at the National Veterinary Services Laboratories (NVSL).

This is the first detection of this virus genotype in dairy cattle (all previous detections in dairy cattle have been HPAI H5N1 clade 2.3.4.4b, genotype B3.13). Genotype D1.1 represents the predominant genotype in the North American flyways this past fall and winter and has been identified in dozens of wild birds and mammals with spillovers into domestic poultry and pets.