The study provides growing evidence of the threat it poses even when cats have no direct exposure to sick dairy cows or poultry.

The report is the latest evidence that the outbreak in dairy herds is spreading undetected in cows, and the spillover into people at highest risk of exposure is going unnoticed.

A new Centers for Disease Control and Prevention study suggests that bird flu may be spreading under the radar in the U.S. In September, the CDC tested 150 veterinarians who primarily worked with cattle in the past three months.