Just one is under quarantine now. Officials believe the source of the Texas infections is dairies across the border in Mexico, although they're unsure how the disease is crossing the Rio Grande. In Michigan, Bender says the culprits generally are believed to be whitetail deer - and, indirectly, people. The illness has been detected in more than 330 deer since 1995, nearly all in the northeastern Lower Peninsula. It's the only sustained outbreak of bovine TB among free-ranging deer ever documented in North America, the USDA says.
Deer are common in Michigan.
But the bovine TB zone is home to numerous hunting clubs that for years dumped huge piles of vegetables in the woods to keep deer alive during winter. With so many eating nose to nose, it was easier for the disease to spread. Deer are believed to have passed bovine TB to cattle by mingling with them in pastures or nibbling at their feed, Bender says. The state has outlawed deer feeding in the TB zone and restricted it elsewhere in the Lower Peninsula, while allowing hunters to kill more deer in the zone. The rate of infection there has been cut in half the last three years.