A genetic analysis of viral samples from a patient in Louisiana hospitalized with the first severe case of bird flu showed mutations that may result in the virus becoming more transmissible among humans, according to the Centers for Disease Control and Prevention.
The agency in its latest update released Thursday said the mutations were not found in samples taken from wild birds, suggesting the virus changed over the course of the patient’s infection.
Angela Rasmussen, a virologist who specializes in emerging infectious diseases, said in a post on the social platform X that it was “good news” the changes to the virus weren’t detected in birds, “because it reduces risk of transmission to another person and suggests ‘human-adapted’ viruses aren’t emerging in birds.”
The Louisiana patient was hospitalized in critical condition with severe respiratory symptoms from bird flu. According to agency officials, the patient had exposure to sick and dead birds in backyard flocks.
The CDC said the mutations in that patient were similar to ones observed in a hospitalized patient in British Columbia, Canada. The changes may make it easier for the virus to bind to receptors in a person’s upper respiratory tract.
“Although concerning, and a reminder that A(H5N1) viruses can develop changes during the clinical course of a human infection, these changes would be more concerning if found in animal hosts or in early stages of infection … when these changes might be more likely to facilitate spread to close contacts,” the CDC said in the report. “Notably, in this case, no transmission from the patient in Louisiana to other persons has been identified.”
Health experts said it’s been expected that the virus would mutate, and while there’s a sliver of good news that the changes happened after infection, it’s still concerning.
“The H5N1 situation remains grim,” Rasmussen wrote. “There has been an explosion of human cases. … More sequences from humans is a trend we need to reverse—we need fewer humans infected, period.”
Michael Mina, an infectious disease immunologist, said on X the situation ought to be a “wake up call” for the U.S. response, which experts said has been extremely lacking.
Former Food and Drug Administration Commissioner Scott Gottlieb said on X that in the “low probability scenario” bird flu develops into a widespread outbreak, the “U.S. will have only itself to blame. Agricultural officials did just about everything wrong over last year, hoping [the] virus would burn out and it didn’t.”
The CDC has confirmed 65 cases of H5N1 bird flu in humans in 2024. Most of the cases were caused by exposure to infected cattle, while others were found in people working at poultry farms and culling operations.
The number of infected cattle herds continues to climb, and California is the most affected state. As of Thursday, 685 herds in the state tested positive for H5N1, according to the U.S. Department of Agriculture. Nationally, there are 901 herds in 16 states infected.
The CDC said the public risk remains low, and the detection of genetic changes “underscores the importance of ongoing genomic surveillance in people and animals, containment of avian influenza A(H5) outbreaks in dairy cattle and poultry, and prevention measures among people with exposure to infected animals or environments.”
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