We’re more concerned even than usual, because this bird flu already has developed the genetic capacity to get into a number of other mammals: seals, mink, foxes, cats and most prominently, and unexpectedly

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 from the CDC showed that bird flu had spread to some veterinarians who did not exhibit any symptoms.