The U.S. Department of Agriculture has detected a bird flu strain in dairy cattle that previously had not been seen in cows, the agency's Animal and Plant Health Inspection Service said on Wednesday. Before this detection, all of the 957 bird flu infections among dairy cow herds reported since the outbreak began last year had been caused by the same strain of the virus, according to the USDA. Nearly 70 people in the U.S. have contracted bird flu, most of them farm workers, as the virus has circulated among poultry flocks and dairy herds, according to the Centers for Disease Control and Prevention. Bird flu has also killed tens of millions of egg-laying hens and has driven egg prices to record highs. The USDA said in a release that genome sequencing of milk from Nevada had identified a different strain present in dairy cows for the first time.