The bird flu strain tearing through American barns for four years has killed two people who contracted it from sick animals. So far, there is no evidence that humans can spread the virus, which remains adapted to avian cells rather than human throats and noses.

Under the right conditions, that barrier could fall. A 2024 study found that a single mutation could shift the dairy strain from preferring bird cell receptors to receptors found in people, raising fears that the virus could gain a foothold in humans and spark a pandemic.

A ProPublica investigation found conditions for such a threat at C&T Fenn Farms in Utah, where bird flu has spread among thousands of mink raised for fur. The outbreak continued uncontrolled for more than two months after state agriculture officials learned in the middle of August that mink were dying.

Mink are particularly concerning because their lungs and airways are remarkably similar on a cellular level to those of people. They have caught and spread other flu viruses, and some mink previously infected humans with COVID-19.

State and federal officials did not order the mink killed or actively monitor exposed workers for symptoms. Flu experts described the response as “irresponsible” and “puzzling,” while one called it “playing with fire.”

If one chicken tests positive for this virulent strain, federal rules require the entire flock to be killed, with poultry farmers reimbursed for their losses. No comparable federal rules govern bird flu outbreaks among mink.

Utah state veterinarian Amanda Price asked the U.S. Department of Agriculture for help, but USDA officials said they did not regulate mink or have an approved vaccine for them. CDC officials spoke with state health employees who were less involved, but they did not speak with Price, and she did not contact them.

Records and interviews showed that Utah officials focused heavily on the farm owner and the potential destruction of his business. “It has been devastating,” Price told ProPublica. “This is his life’s work that he’s seeing be destroyed. I really hope that you understand the humanity behind this situation.”

A fur trade representative warned Price that killing the mink could destroy the business and ultimately the industry. Tom Peacock, an avian influenza researcher at the Pirbright Institute, said other countries confronting H5N1 on fur farms moved quickly to depopulate them.

Officials also failed to monitor mink workers even though CDC guidance urges such surveillance. Utah health officials previously conducted active monitoring, but stopped after agriculture officials complained that farmers were annoyed and becoming less willing to cooperate.

Under a 2025 agreement, the Utah Department of Agriculture and Food agreed to share information about farm outbreaks as long as health officials did not track workers’ health. Pamela Gomez Pinedo, a respiratory disease epidemiologist for Utah’s health department, said monitoring would occur only with evidence of human to human transmission.

That policy left a glaring question about how officials would detect such transmission without testing workers. Price said the approach allows farmers to decide whether to contact health officials, adding that the response would change if people began actively dying.

Eye redness appears in more than 90% of human bird flu cases and is often the only symptom. A ProPublica reporter found two farm workers, including one with a visibly red eye, but the health department did not recommend testing after owner Chad Fenn said dust had entered the worker’s eye.

Genomic analysis of mink lung and brain samples showed they carried the same strain spreading through dairy herds. Officials did not know whether contaminated beef caused the outbreak, although Fenn said the mink routinely eat raw livestock organs, including organs from cows.

Scientists are also concerned about reassortment, which can occur when another flu virus infects the same cell and exchanges genetic material with bird flu. The risk grew more troubling as September brought one of the earliest flu season starts on record, rather than the usual acceleration in November.

Initial genetic sequences from dead mink showed no especially concerning mutations, according to experts and the CDC. Experts nevertheless said the virus would have continued mutating during two additional months of spread, while Price said she was still awaiting results from newer samples taken two weeks earlier.

Communications obtained through Utah’s public records law showed officials worked to protect the farm’s privacy and avoided declaring an emergency because it “may alert animal rights groups.” One local health department spokesperson told ProPublica that a possible bird flu outbreak “would be news to me.”

Price had not visited the property and relied on conversations with the owner and veterinarian, along with Google Maps. She imposed a verbal hold on moving mink, manure or carcasses, but experts warned that without active surveillance, officials cannot credibly claim the virus has not spread.

Fenn said the virus continued spreading at a slower pace and rejected concerns that mink posed an unusual danger. Peacock offered a stark assessment of conditions at the farm: “I would want a full on hazmat suit if I were on that farm. Or, preferably, I’d rather not to be on that farm.”