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The ongoing spread of avian influenza (bird flu) in the United States has sparked growing concerns among health experts, particularly with the emergence of new mutations of the virus and troubling cases of infections in cats.
A recent analysis by the Centers for Disease Control and Prevention (CDC) revealed that a sample of the H5N1 virus taken from a critically ill patient in Louisiana showed signs of mutating in ways that could potentially enhance its ability to infect human airways. While the mutations were found only in this individual, and there is no evidence to suggest the altered strain has spread beyond the patient, the discovery has heightened alarm over the virus’s potential to adapt to human hosts.
The Louisiana patient, an elderly individual, was reported to be in “critical condition” earlier this month after contracting H5N1, which is known for its high fatality rate in birds. Upon closer examination, the CDC found that a small percentage of the virus in the patient’s throat carried genetic changes that could allow it to bind more efficiently to receptors in the human upper respiratory tract.
However, the CDC emphasized that these mutations had not been detected in birds, including in the backyard poultry flock where the patient is believed to have contracted the virus. The agency suggested that the mutations likely occurred as a result of the virus replicating in the patient’s body, given the severity of their illness. At this time, there has been no evidence of the mutated virus spreading to other humans.
Experts caution that it is too early to draw conclusions about the potential implications of these changes. Angela Rasmussen, a virologist at the University of Saskatchewan in Canada, noted that while the mutation might improve the virus’s ability to enter cells, further research and animal testing are necessary to assess whether it could make the virus more transmissible or virulent.
“Similar mutations have occurred in previous critically ill patients without leading to broader outbreaks,” Rasmussen said. “It’s important to monitor, but we’re not at a point where we can predict an imminent pandemic.”
Thijs Kuiken, a virologist at Erasmus University Medical Center in the Netherlands, echoed this view, emphasizing that while the ability of the virus to bind to human cell receptors is necessary for transmission, it is not sufficient on its own. For the virus to spread effectively among humans, other factors must also align, he explained.
While the mutation itself may not necessarily result in a more severe disease, it could potentially lead to milder infections, as it may favor infection in the upper respiratory tract, causing symptoms like a sore throat or runny nose, rather than targeting the lower respiratory tract, which leads to severe pneumonia.
The Growing Threat of Animal Infections
While the potential for human-to-human transmission remains uncertain, another worrisome development has been the rising number of animal infections. Earlier this month, an Oregon cat died after consuming raw pet food contaminated with H5N1. Genome sequencing confirmed that the virus found in the food matched the strain that killed the cat, which had been an indoor-only pet and had not been exposed to the virus in its environment.
The incident prompted a recall of Northwest Naturals’ Feline Turkey Recipe raw pet food, highlighting the risk of animal-to-animal transmission through contaminated products. Additionally, in Washington State, 20 big cats at a sanctuary died after contracting the virus, according to a statement from the Wild Felid Advocacy Center of Washington.
Rasmussen warned that such infections in animals could increase the risk of human exposure. “If you have an outdoor cat that gets H5 from eating a dead bird,” she explained, “and that cat comes back into your house and you’re snuggling with it, you’re sleeping with it… that creates additional exposure risk.”
As the virus continues to circulate widely, the CDC has reported 65 confirmed human cases of H5N1 in 2024, with many more potentially going undetected, particularly among poultry workers and those in close contact with infected animals. This widespread circulation raises concerns about the possibility of the virus mixing with seasonal influenza, which could trigger rapid evolutionary changes, similar to those that led to the 1918 and 2009 flu pandemics.
Experts stress the need for continued vigilance, but caution against panic. The current mutation, while concerning, is only one of many factors that need to align before the virus can pose a broader threat to public health. As health officials monitor both human and animal cases, the focus remains on containment and further study of the virus’s behavior.
