Nevada confirms state’s first human case of H5N1 in dairy worker

The Central Nevada Health District has reported the first confirmed case of H5N1 avian flu in a human within the state. The individual, a dairy farm worker in Churchill County, was exposed to infected cattle.

According to the CNHD, the worker exhibited only conjunctivitis as a symptom and is currently recovering. Health officials are reaching out to those who may have had contact with the infected individual and are providing them with protective equipment and antiviral medication. So far, there is no indication that the virus is spreading between people.

“While the current public health risk to the general public remains low, people who work with birds, poultry, or cows, or have recreational exposure to them, are at higher risk,” the CNHD stated.

The report did not specify the genotype of the virus found in the patient, but previous detections in Churchill County have identified the D1.1 genotype. This represents the emergence of a second H5N1 strain in cattle, differing from the earlier B3.13 genotype associated with prior dairy farm outbreaks.

The D1.1 strain is widely found in migratory birds and has been responsible for several human infections, some of which were severe.

The Centers for Disease Control and Prevention has added this case from Nevada to its list of confirmed human infections since early 2024. That total now stands at 68 cases, with 41 involving dairy workers.

The U.S. Department of Agriculture Animal and Plant Health Inspection Service released a technical briefing on February 7 regarding the detection of the D1.1 H5N1 genotype in Nevada dairy cattle. The report includes new investigative findings and genetic sequencing data.

Originally, APHIS confirmed the presence of the virus in Nevada through milk testing. In early January, three out of eleven tested silo samples were found to contain avian influenza, with confirmation provided by the USDA National Veterinary Services Laboratory on January 10.

Subsequent investigations revealed that milk from up to 12 dairies may have contributed to the positive samples. Additional testing of on-farm bulk milk detected the virus at two of these dairies. Whole-genome sequencing confirmed the presence of the H5N1 2.3.4.4 lineage and the D1.1 genotype in multiple bulk milk samples from a single herd. A partial sequence indicative of D1.1 was also identified in a second herd.

Interestingly, the cattle did not show symptoms of illness until after the virus was detected. Both dairy operators reported large numbers of wild bird deaths near their facilities prior to the outbreak.

The D1.1 genotype affecting dairy cattle is closely related to the virus strains found in migratory birds across North American flyways.

Although sequencing did not detect mutations in the hemagglutinin gene that would enhance mammalian transmission, scientists identified a D701N mutation in the polymerase basic protein 2 (PB2) gene. This mutation has previously been associated with mammalian adaptation and was found in samples from four cows.

APHIS researchers noted that this mutation has not been detected in D1.1 viruses from wild birds or in dairy cows infected with the B3.13 genotype. However, it has appeared in some human infections, with no signs of further transmission between individuals.

In its latest update, APHIS confirmed three additional H5N1 cases in livestock — two in Nevada and one in California. This brings the national count to 962 detections, with 739 cases in California and seven now recorded in Nevada.