The virus has spread rapidly in California, the nation’s largest producer of milk. Farmers are frustrated that their herds are getting infected despite various precautions.

Most worrying, though, is the spillover from livestock to humans. So far, 58 people in the United States have tested positive for bird flu. Fifty-six of them worked either on dairy or poultry farms where millions of birds had to be culled.

Amid growing fears that the virus associated with bird flu could become a public health crisis in the U.S., Michigan is testing the milk coming out of its dairy farms to