That's the way one scientist puts it — referring to how infected wild birds survive long enough to spread it to birds and mammals around the world. And that's a serious risk for human health.

Three veterinarians had antibodies to bird flu virus, which suggests recent infection, the report said. None of them knew they were working with dairy cattle with known or suspect

Bird flu infections were detected among veterinarians tested last fall, including two people with no known exposure to animals with the virus, according to a report released by the U.S. Centers for Disease Control and Prevention on Thursday.