The U.S. Department of Agriculture said this week that cow-to-cow transmission is a factor in the spread of bird flu in dairy herds, but it still does not know exactly how the virus is being moved around. Dairy herds in eight states tested positive over the past month, along with one dairy worker in Texas. "Those of us that have worked with influenza for a long time were fairly quickly saying, 'Yep it moves cow to cow,'" Jim Lowe, an associate dean at the University of Illinois College of Veterinary Medicine, said on Friday.