Mycobacterium avium subspecies paratuberculosis

Johne's disease is a widespread farm animal disease, causing diarrhea, wasting and death, primarily in dairy cattle. It also affects sheep, goats, deer, antelope and llamas. It is a concern to the domestic cattle industry because cattle lose weight and their milk production drops. Since there are no adequate control mechanisms in place it will become even more common. Anti-microbial treatments for Johne's do not cure the disease and a vaccine is not a reliable way to stop it. Some scientists are raising the alarming possibility that the microbe causing the illness may be passed on to humans via milk; an association is also made with Crohn's disease in humans.

In the USA, the incidence of Johne's disease is rising. Infected cattle continue to be used for milk production (pasteurization of milk is considered by the industry to kill the bacteria that dairy cattle excrete into the milk) and are then slaughtered, mainly for ground beef. While the full extent of the disease is difficult to assess because of limited testing for it, federal officials and the dairy industry estimate on the basis of a 1996 national survey that some dairy cattle are infected in about 22 percent of herds across the country (perhaps 50 percent or higher in some areas). The disease costs farmers about $200 million each year.