The highly pathogenic avian influenza (H5N1) virus, which has been circulating in wild birds for years, has now been detected in dairy cows in the United States, raising concerns about its potential to spread to humans. The virus has been found in nearly three dozen dairy herds in eight states, and inactive viral remnants have been detected in grocery store milk. Scientists are concerned that the virus could mutate to become more easily transmissible among people, as it has been known to adapt to spread among different species. The USDA has ordered that all lactating dairy cows in the U.S. be tested for the virus before they can be moved between states, and experts are urging increased surveillance and testing to monitor the outbreak and prevent its further spread.