On Jan. 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.
The confirmation was a result of State tracing and investigation following an initial detection of silo testing under the USDA’s National Milk Testing Strategy (NMTS) in Nevada.
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USDA APHIS continues to collaborate with the Nevada Department of Agriculture by conducting additional on-farm investigations and testing and gathering additional epidemiological information to better understand this detection and limit the spread of disease.
The Nevada case is the first detection of the 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.
