The ongoing spread of bird flu in the United States has alarmed experts — not just because of human cases causing severe illness, but also due to troubling new instances of infections in cats.
A sample of the virus found in a critically ill patient in the United States has shown signs of mutating to better suit human airways, although there is no indication it has spread beyond that individual, authorities report.
Earlier this month, officials announced that an elderly Louisiana patient was in "critical condition" with a severe H5N1 infection.
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