A genetic mutation of the H5N1 bird flu virus — a mutation associated with increased infectiousness and disease severity — has been found in two cats, in what scientists say is another indication of the risks posed by the virus.

Two cats in two separate New York City households have tested positive for bird flu, the city health department says.

One of the kittens infected with the bird flu was an 8-month-old kitten on the Upper West Side that consumed raw chicken from a company that makes raw pet food.