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CDC: Bird flu virus that infected Michigan dairy farmer capable of airborne transmission
The strain of bird flu that infected a Michigan dairy farmworker is capable of airborne transmission, amping up concerns about its potential to spark a new pandemic, according to a research letter published in June.
In recent years, the H5N1 avian influenza virus has spilled over from birds to a growing number of mammals, including cats, skunks, raccoons, oppossums, rodents and bears. It was first identified in dairy cows in 2024, and then leaped from cows to humans.
In May 2024, two Michigan dairy farmworkers contracted the virus. The first reported conjuctivitis, also known as pink eye, as the only symptom. The second Michigan farmworker's symptoms were a little bit different. That person reported upper respiratory tract symptoms, including cough without fever, and eye discomfort with watery discharge. Both recovered.
Researchers isolated the virus from a swab used to collect a sample from the eye of one of the infected workers. That virus — clade 2.3.4.4b, genotype B3.13 — was studied to determine how transmissible it is, and the ways it spreads.
"Because avian H5N1 viruses cross the species barrier and adapt to dairy cattle, each associated human infection presents further opportunity for mammal adaption," the study authors wrote in "Emerging Diseases," a peer-reviewed journal of the U.S. Centers for Disease Control and Prevention. "This potential poses an ongoing threat to public health and requires continual surveillance and risk assessment ... to improve our ability to predict and prepare for the next influenza pandemic."
Scientists infected ferrets with that type of virus. Six of the infected ferrets were put in the same living space as six healthy ferrets, and within a week, all of them had bird flu, showing that direct contact spreads the disease.
Six other healthy ferrets had no direct contact with the infected animals, but were breathing the same air as ferrets with H5N1 bird flu, and inhaled respiratory droplets. Three of those six previously healthy ferrets became infected, the study found, suggesting an airborne infection rate of 50%.
Researchers also collected aerosol samples daily from three infected ferrets, and found evidence of airborne virus particles in samples from all three animals.
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Ferrets have been used for decades in medical research studies, especially those involving flu viruses, because their lung physiology is similar to humans. They also have similar receptors in the respiratory tract that influenza viruses bind to.
All of the infected ferrets survived the 21-day study, researchers said, recovering from moderate disease. On average, ferrets infected with H5N1 bird flu lost nearly 10% of their body weight and had fevers. They were lethargic, and had nasal and ocular discharge along with sneezing.
Since 2022, there have been 70 confirmed and probable human cases of bird flu in the U.S. One person in Louisiana, who was exposed to wild birds and a backyard flock, died. To date, there have been no reports of human-to-human transmission, according to the CDC.
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The CDC says the risk to the average American from bird flu remains low, but it's higher for people who work with animals on farms, at zoos and other animal facilities.
Contact Kristen Shamus at kshamus@ Subscribe to the Detroit Free Press.
This article originally appeared on Detroit Free Press: Virus that infected Michigan dairy farmer capable of airborne spread
