Another spillover of the H5N1 bird flu virus from wild birds to dairy cattle appears to have occurred, this time in Arizona.

The study published Thursday by the Centers for Disease Control and Prevention echoes two smaller ones that detected evidence of infection in previously undiagnosed farmworkers. In those studies, several of the infected workers remembered having symptoms of H5N1 bird flu, while none of the veterinarians in the new paper recalled any such symptoms.

A new study published by the U.S. Centers for Disease Control and Prevention shows that the H5N1 bird flu virus is likely circulating undetected in livestock in many parts of the country and may be infecting unaware veterinarians.