The Central Nevada Health District (CNHD) today said it has confirmed the state’s first human infection from H5N1 avian flu, which involves a worker who was exposed to sick cows at a dairy farm in Churchill County.
In its announcement, the CNHD said conjunctivitis was the only symptoms and that the worker is recovering.
Close contacts and other people who may have been exposed are being contacted and monitored for symptoms. Officials have offered them personal protective equipment and antivirals. So far, no sign of human-to-human spread has been reported.
“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 said.
The report didn’t note a genotype from the patient’s sample, but recent detections in Churchill County involved the D1.1 genotype, which marked the spillover of a second H5N1 genotype from cattle, one that’s different from the B3.13 genotype implicated in earlier dairy cattle outbreaks.
D1.1 is widely circulating in wild migratory birds and has been linked to a few illnesses in humans, some of them severe.
The Centers for Disease Control and Prevention (CDC) added the Nevada case to its list of confirmed human cases since early 2024, which now stands at 68 cases, 41 of them involving dairy workers.
Nevada cows didn’t have clinical signs until after testing
In other developments, the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) on February 7 published a technical briefing on the recent detection of the D1.1 H5N1 genotype in Nevada dairy cows, which also contained new details about the investigation and information from genetic sequencing.
In the initial announcement, APHIS had said the detections came from milk testing in Nevada. It said 3 of 11 silo samples collected in early January were positive for avian influenza, which was confirmed on January 10 at the USDA National Veterinary Services Laboratory.
Investigators determined that as many as 12 dairies could have contributed milk to the silos that tested positive. On-farm bulk milk samples were collected and tested, and avian flu was found at two of the dairies. Whole-genome sequencing confirmed the H5N1 2.3.4.4 lineage and the D1.1 genotype in four bulk milk samples from one herd. Scientists also found a partial sequence consistent with D1.1 from a second herd.
Clinical signs in the cows didn’t develop until after the detections, and both producers reported large wild bird die-offs near their facilities.
Mutation linked to mammalian adaptation
The D1.1 genotype found in dairy cattle is closely related to the virus circulating in wild migratory birds across different North American flyways.
Though sequencing didn’t identify any mutations in the hemagglutinin gene of the dairy cow virus that would make it more easily infect mammals, investigators did find the D701N mutation in the polymerase basic protein 2 (PB2) gene that has been linked to mammalian adaptation before in samples from four cows.
APHIS scientists said D701N hasn’t been found in D1.1 viruses from wild birds or in dairy cows with B3.13 genotype viruses. They added, however, that the mutation has turned up in human cases, with no evidence of onward spread.
The group praised the quick action of the Nevada Department of Agriculture in enrolling herds in the national milk testing program and in quarantining the affected herd to prevent the spread beyond the local area.
In its latest updates, APHIS today confirmed three more H5N1 detections in livestock, two in Nevada and one in California. The additions lift the national total to 962, including 739 in California and now 7 in Nevada.
