Bird flu virus shows signs of worrisome mutation: CDC

Samples from a patient who recently developed the first severe case of H5N1 bird flu in the U.S. showed mutations that may make it easier for the virus to bind to cell receptors in the human upper respiratory tract, according to a Dec. 26 update from the CDC. 

On Dec. 18, the agency confirmed that a patient in Louisiana had been hospitalized with a severe bird flu infection, marking the first human case of severe illness tied to the H5N1 virus in the country. The individual, who is older than 65 and has underlying medical conditions, was exposed to sick and dead birds in backyard flocks. 

A genetic analysis of two samples from the patient showed mutations in the hemagglutinin (HA) gene, which plays a significant role in binding to host cells. The changes "may result in increased virus binding of a2-6 cell receptors found in the upper respiratory tract of humans," the CDC said in its summary of the analysis. The mutations were not identified in samples taken from wild birds on the patient's property, indicating the mutation likely developed during the patient's course of infection and is not widely circulating in wildlife. 

The patient was infected with the D1.1 genotype virus, which is closely related to other viruses spreading among wild birds and poultry, though different from the B3.13 genotype spreading widely among dairy cows, poultry and sporadic human cases in multiple states. One of the identified mutations was also found in a severe case reported in British Columbia, Canada. 

"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. 

The agency also emphasized that there has been no evidence the patient transmitted the disease to anyone else and that its risk assessment surrounding the H5N1 outbreak's threat to public health remains low. 

Since April, there have been at least 65 cases of H5N1 bird flu among humans in the U.S. Federal officials have reiterated that the nation's bird flu outbreak does not pose an immediate threat to public health, but infectious disease experts say recent developments suggest its spread is heading in the wrong direction. Read more updates on the scope of the outbreak and developments experts have their eye on here

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