The Central Nevada Health District (CNHD) has confirmed the state’s first human case of avian influenza A (H5N1) in an adult exposed to infected dairy cattle at a Churchill County farm. The individual experienced conjunctivitis as the only symptom and is currently recovering. According to the Centers for Disease Control and Prevention (CDC), the risk to the general public remains low.
Officials report no evidence of human-to-human transmission. Close contacts and other farm workers potentially exposed to the virus are being monitored, offered personal protective equipment (PPE), tested, and provided with antiviral medication as a precaution. No additional cases have been confirmed at this time.
Emerging Viral Strain and Dairy Farm Infections
The CNHD did not specify the genotype of the virus in the infected worker. However, recent detections in Churchill County identified the D1.1 genotype, a second H5N1 strain that has spilled over into cattle. This genotype differs from B3.13, which was linked to earlier dairy cattle outbreaks.
D1.1 is widely circulating among wild migratory birds and has been associated with a handful of human cases, some of which were severe. The CDC has now recorded 68 human cases of H5N1 in the United States since early 2024, with 41 of them involving dairy workers.
Dairy Cows Showed No Symptoms Until After Testing
The U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) recently published a technical briefing detailing the detection of the D1.1 H5N1 genotype in Nevada dairy cows. Initial findings came from milk testing, with three of 11 silo samples collected in early January testing positive for avian influenza. The USDA National Veterinary Services Laboratory confirmed the presence of the virus on January 10.
Investigators traced the contaminated milk back to at least 12 dairies. Further on-farm testing confirmed the H5N1 2.3.4.4 lineage and the D1.1 genotype in multiple samples. Notably, dairy cattle did not display symptoms until after the positive test results, and affected farms reported significant wild bird die-offs near their facilities.
Mutation Raises Concern Over Mammalian Adaptation
Genetic sequencing of the dairy cattle virus found no mutations in the hemagglutinin gene that would increase its ability to infect mammals. However, scientists did detect the D701N mutation in the polymerase basic protein 2 (PB2) gene, a marker previously linked to mammalian adaptation.
The D701N mutation has not been identified in D1.1 viruses from wild birds or in dairy cows infected with the B3.13 genotype. While this mutation has been observed in human H5N1 cases, there is currently no evidence of onward transmission.
Precautions for Farm Workers and Public Health Recommendations
While the overall public health risk remains low, individuals working with poultry, livestock, or wild birds face a higher risk of exposure. Health officials recommend the following precautions:
- Avoid direct contact with sick or dead animals, their droppings, and contaminated surfaces.
- Prevent pets from interacting with infected wildlife.
- Ensure proper food safety by cooking poultry, eggs, and dairy products to appropriate temperatures and avoiding unpasteurized milk or cheese.
- Receive the seasonal flu vaccine to reduce the risk of co-infection, although it does not prevent avian influenza.
- Report sick or dead birds to USDA Wildlife Services at (775) 851-4848 and notify veterinarians or the Nevada Department of Agriculture about affected livestock.
Anyone exposed to sick or dead birds or working on a farm where avian influenza has been detected should monitor for respiratory symptoms or conjunctivitis. Those who develop symptoms within 10 days of exposure should inform their healthcare provider about their contact with potentially infected animals and follow appropriate medical guidance.
Ongoing Surveillance and National Response
In its latest update, APHIS confirmed three additional H5N1 detections in livestock—two in Nevada and one in California. This brings the national total to 962 cases, including 739 in California and seven in Nevada.
The USDA continues to monitor the outbreak closely, with state and federal agencies implementing measures to control the spread of the virus in dairy cattle and limit potential transmission risks to humans.
