New bird flu mutation discovered in US, as cat infections cause alarm

The ongoing spread of bird flu in the US has alarmed experts - not just because of human cases causing severe illness, but also due to troubling new instances of infections in cats.

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A sample of the virus found in a critically ill patient in the US has shown signs of mutating to better suit human airways, although there is no indication it has spread beyond that individual, the authorities report.

Earlier in December, officials announced that an elderly Louisiana patient was in "critical condition" with a severe H5N1 infection.

An analysis posted by the Centers for Disease Control and Prevention (CDC) on Dec 27 revealed that a small percentage of the virus in the patient's throat carried genetic changes that could increase the virus' ability to bind to certain cell receptors found in the human upper respiratory tract.

Importantly, the CDC noted that these changes have not been detected in birds - including in the backyard poultry flock believed to have been the source of the patient's initial infection.

Instead, the agency said the mutations were "likely generated by replication of this virus in the patient with advanced disease", emphasizing that no transmission of the mutated strain to other humans had been identified.