New version of bird flu infects Nevada dairy worker
A Nevada dairy worker was infected with a version of bird flu that is known to have killed one person in the United States and severely sickened a teen in Canada, state and federal health authorities said.
This version of the virus was detected for the first time in dairy farms last month in Nevada. The Central Nevada Health District said Monday that an adult was exposed to infected dairy cattle while working at a farm in the northwestern part of the state. The Centers for Disease Control and Prevention said its genetic analysis confirmed that the virus in the Nevada person is the same as was detected in the Nevada dairy cows.
The Nevada worker had conjunctivitis, commonly known as pink eye, but no other reported symptoms. The worker is recovering, the district said, and close contacts and other workers exposed at the farm are being contacted and monitored for symptoms. They are being offered personal protective equipment, testing and antiviral medication, the district said. No additional cases have been confirmed.
The latest development comes after federal agriculture officials announced last week that they had identified this version of the virus in dairy herds in Nevada. The discovery of this version, called D1.1, has raised concerns among experts that dairy cows may be more susceptible to the H5N1 virus, thereby increasing the risk of cow-to-human spread, especially for farmworkers and others in close contact with the animals.
The CDC said in a statement that this case involving “cow-to-human spread of H5 in a person with higher-risk occupational exposure does not change CDC’s risk assessment, which remains low for the public but is higher for people with occupational or recreational exposures.”
There is currently no evidence of person-to-person spread of H5N1 bird flu from the worker in Nevada to others. “Combined with the mild nature of the individual’s illness, this case does not change CDC’s low risk assessment for the public,” the agency said.
This version of the virus is circulating broadly in wild birds and is likely to have infected 15 people in Iowa, Louisiana, Oregon, Washington and Wisconsin during 2024, the CDC said.
It is different from the B3.13 virus that has caused dairy cow outbreaks and the majority of the 68 human infections in the United States since the outbreak among cows was first disclosed in March 2024. Most of the infections in people have been mild, regardless of which version of the virus infected them.
The exception is the fatal case of a Louisiana man - the first U.S. bird flu death - who had prolonged, unprotected exposure to infected backyard birds, the CDC said. The D1.1 version of the virus also sickened a teen in Canada, who probably became infected from exposure to poultry or wild birds, because the virus in her was closely related to viruses circulating in wild birds in British Columbia, experts have said.
The D1.1 version of the virus in the Nevada worker contains a genetic mutation that has previously been linked to more efficient virus replication in people and other mammals, the CDC said. But no other mutations were identified. The agency also did not identify any changes that would suggest decreased effectiveness of current antiviral treatments, such as Tamiflu.
The infection of the Nevada worker is concerning, but not that surprising because officials and experts still do not have the full picture of how the H5N1 virus spreads to humans and how sick they get.
“The cow has now served as a vehicle for onward transmission to humans,” said Abraar Karan, an infectious-disease physician at Stanford University.
For months, experts and health officials have underscored the importance of farmworkers using appropriate personal protective equipment to protect against splashes of milk or feathers and dust in poultry farms.
The infection in the Nevada dairy worker suggests the requirement for personal protective equipment “was breached or something was not being cleaned properly,” Karan said.
The finding of D1.1 in the Nevada dairy cows raises questions about early assumptions by federal agriculture and health officials that the outbreak in dairy cows in spring 2024 began when the virus jumped from birds to cows in the Texas panhandle last year in a single event.
The detection of D1.1 in Nevada cows “is the second spillover event from migratory wild birds to dairy cattle,” the U.S. Agriculture Department has reported. Agriculture officials found the virus after testing raw milk collected from a silo as part of a national milk testing strategy begun last year by the USDA. It’s not clear how this version of the virus spilled into the Nevada herds. The affected dairy producers in Nevada had reported large wild bird die-offs near the dairies. -
The Washington Post