The finding indicates that the virus, known as H5N1, has spilled from birds into cows at least twice — leading to these two sets of infections — and that it could continue to do so. It also suggests that the virus may pose a persistent risk to cows and to the people who work closely with them.

FRIDAY, Feb. 14, 2025 (HealthDay News) -- Three U.S. dairy veterinarians unknowingly had H5N1 infections, otherwise known as bird flu. This included one person who worked only in states without known outbreaks in cows, according to a new study from the U.S. Centers for Disease Control and Prevention (CDC).

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.