Scientists also are not sure the Johne's bacteria are destroyed when milk is pasteurized. Even if they are, there is still concern the bacteria could reach humans through undercooked meat, unpasteurized dairy products or fecal contamination of underground water supplies. Dairy cows that are no longer productive are routinely slaughtered for ground beef. The producers are very edgy about the whole thing. Johne's was first identified more than a century ago, but many farmers paid it little heed.
Cattle can carry the infection for years before showing symptoms.
An Agriculture Department study in 1996 found that 22 percent of U.S. herds had at least 10 percent of their cattle infected with Johne's. Kevin Condon, a dairy farmer near Oshkosh, Wis., said the disease was found in his herd more than 10 years ago. He has kept it under control by testing his cattle when he can afford it, taking precautions with calves, and being more careful in handling of manure and feed. Sick cattle are sent to slaughter. The industry is learning more and more about it, and how to deal with it better.