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Health authorities have confirmed that the bird flu virus detected in a critically ill patient in the United States has undergone a mutation, enhancing its ability to infect human airways. Despite this concerning development, officials have emphasized that there is currently no evidence suggesting the virus has spread to others beyond this single case.
In a concerning update earlier this month, authorities reported that an elderly patient in Louisiana was hospitalized in critical condition after being infected with a severe case of the H5N1 virus.
An analysis posted by the CDC on Thursday pointed out that a small percentage of the virus detected in the patient’s throat had undergone genetic changes that could lead to increased binding to certain receptors in the human upper respiratory tract, a factor that may heighten the virus’s potential for human infection.
These genetic changes, crucially, have not been detected in birds, including the backyard poultry flock that is believed to have initially infected the Louisiana patient. The CDC clarified that the mutations were probably generated by the virus replicating in a patient with severe disease. Moreover, the agency stated that there has been no indication of the mutated virus being transmitted to other humans.
Experts contacted by AFP said it was too early to determine whether these changes would make the virus spread more easily or cause more severe disease in humans.
The particular mutation “is one step that is needed to make a more efficiently transmissible virus,” said Angela Rasmussen, a virologist at the University of Saskatchewan in Canada. “But I do want to point out that it’s not the only step.”
Read also: Bird Flu: US Confirms First Case Without Animal Contact
She explained that while the mutation might mean the virus can more easily enter cells, this would need to be confirmed through further testing on animals. Moreover, similar mutations have been found in severely ill patients in the past without triggering wider spread among humans.
“It’s good to know that we should be looking out for this,” she said, “but it doesn’t actually tell us, ‘Oh, we’re this much closer to a pandemic now.’”
Another expert, Thijs Kuiken of Erasmus University Medical Center in the Netherlands, agreed with Rasmussen.
“Efficient attachment to human upper respiratory tract cells is necessary, but not sufficient, for more efficient transmissibility between people,” he said, “because the attachment process is but one of several steps in the virus replication cycle in a human cell.”
Rasmussen expressed greater concern about the overall level of bird flu currently circulating rather than this specific case.
The CDC has reported 65 confirmed human cases of bird flu in the United States in 2024, with more likely going undetected among dairy and poultry workers.
