APHIS confirms D1.1 genotype in dairy cattle in Nevada
On January 31, 2025, the USDA Animal and Plant Health Inspection Service (APHIS) National Veterinary Services Laboratories (NVSL) 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. This confirmation was a result of State tracing and investigation, following an initial detection on silo testing under the USDA’s National Milk Testing Strategy (NMTS) in Nevada.
This genotype has been associated with severe infections in humans. The D1.1 variant of the virus was linked to the first reported death in the U.S. related to avian influenza, as well as to a severe illness in Canada. A resident of Louisiana passed away in January after developing severe respiratory symptoms following contact with wild and backyard birds. In British Columbia, a teenage girl was hospitalized for several months due to a virus traced to poultry.
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 wild birds, mammals, and spillovers into domestic poultry. The detection does not change USDA’s HPAI eradication strategy and is a testament to the strength of our National Milk Testing Strategy (NTMS).
