A mutation of the bird flu virus found in a critically ill patient in the United States has shown adaptations that may make it better suited to human airways, health authorities revealed. However, there is no evidence of transmission beyond the individual case.
The Centers for Disease Control and Prevention (CDC) disclosed that the mutation was detected in an elderly Louisiana patient who remains in critical condition with a severe H5N1 infection. Officials believe the patient was infected through contact with a backyard poultry flock.
In a report released Thursday, the CDC highlighted genetic changes in the virus sampled from the patient’s throat. These changes may enhance the virus’s ability to bind to cell receptors in the upper respiratory tract of humans, potentially facilitating human infection.
Crucially, the CDC clarified that these mutations were not present in birds and are believed to have emerged during replication of the virus within the patient. The agency emphasized that no evidence of further human-to-human transmission has been observed.
Experts have urged caution, noting the mutation represents one of several steps necessary for the virus to become more transmissible among humans.
“This mutation improves the virus’s ability to enter human cells, but it’s not enough on its own to make it highly contagious,” said Angela Rasmussen, a virologist at the University of Saskatchewan in Canada. Further testing is needed to determine whether the mutation affects transmissibility or severity in humans.
Rasmussen also noted that similar mutations have been observed in past cases of severe illness without resulting in broader outbreaks. “It’s a sign to remain vigilant, but it doesn’t mean we are on the brink of a pandemic,” she added.
Thijs Kuiken, a virologist at Erasmus University Medical Center in the Netherlands, echoed this sentiment. “Efficient attachment to human upper respiratory cells is necessary but only one step in a complex replication cycle,” he said.
The CDC has reported 65 confirmed human cases of bird flu in the U.S. in 2024, primarily among individuals with direct exposure to infected poultry. Experts warn that the high prevalence of bird flu in animals increases the risk of reassortment with seasonal influenza, potentially resulting in rapid evolution of the virus.
“This ongoing circulation of bird flu in avian populations is a bigger concern,” Rasmussen cautioned, pointing to the possibility of genetic mixing that could lead to more dangerous viral strains, as seen in the pandemics of 1918 and 2009.
Health officials continue to monitor the situation closely, emphasizing that public awareness and preventive measures are key to minimizing risks.
