WASHINGTON — A new genotype of H5N1 has been discovered in dairy cattle in Nevada, according to the US Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS).

The initial H5N1 detection was found through silo testing under the USDA’s National Milk Testing Strategy (NMTS). USDA then began investigating and tracing the virus. Through whole genome sequencing, the National Veterinary Services Laboratories confirmed the first detection of H5N1 clade 2.3.4.4b, genotype D1.1 in dairy cattle.

The D1.1 genotype is most commonly found in wild birds. This past fall and winter, the USDA reported the genotype in mammals and domestic poultry.

All detections of the virus in dairy cattle before the Nevada case have been H5N1 clade 2.3.4.4b, B3.13 genotype.

USDA said the appearance of the D1.1 genotype in dairy cattle does not change its eradication strategy for highly pathogenic avian influenza (HPAI).

The agency called the detection “a testament to the strength of our National Milk Testing Strategy,” which currently includes 40 states enrolled in the program.

USDA is continuing to work with the Nevada Department of Agriculture to conduct additional on-farm investigations and testing while gathering epidemiological information to better understand the new appearance of the genotype and limit the spread of the disease.

In December 2024, the first detection of the D1.1 genotype in a human was found in a Louisiana patient who was hospitalized and considered the first severe H5N1 case. Prior to that, the Centers for Disease Control and Prevention (CDC) had identified the B3.13 genotype in most patients. In total, CDC has confirmed 68 human cases of H5N1.

On Jan. 6, the CDC reported the first death due to the disease, which occurred in a Louisiana patient.

“While tragic, a death from H5N1 bird flu in the United States is not unexpected because of the known potential for infection with these viruses to cause severe illness and death,” the CDC said.

The agency noted that outside of the United States, more than 950 human cases of H5N1 have been reported to the World Health Organization, with approximately half of those cases resulting in death.

CDC maintains that the risk of HPAI to the general public is low.

To date, nearly 12,000 wild birds have been affected by the disease, 157.8 million poultry and 968 dairy herds.