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in the body of the report in which Map as a disease agent is discussed in the larger context of its position in the MAC.
Control of JD on farms has been difficult for several reasons. The disease has a long subclinical phase, during which animals can spread the infection without themselves exhibiting signs of illness. Current diagnostic tests are relatively insensitive at detecting this phase of the disease. It thus is a simple matter for a producer to unknowingly purchase a Map-infected animal, which can then spread the infection throughout a herd. Subsequent detection of JD in a herd can be delayed because of a lack of producer awareness, poor sensitivity of diagnostic tests when applied to individual animals, and the fact that JD is clinically similar to other common ruminant diseases. Finally, the lack of an efficacious vaccine means that control is undertaken primarily through management practices that are designed to interrupt transmission of the agent. Producers often are slow to adopt those new methods, however, because they often fail to recognize JD as a problem of sufficient economic importance to warrant dramatic management changes. This reluctance could limit the success of control programs that focus exclusively on Map as the disease agent.
Historically, control of JD in the United States has been left to the discretion of individual states. Some states have no program at all, others have chosen from a variety of voluntary options. The United States Animal Health Association has attempted to provide more coordination through the creation of its National Johne’s Disease Working Group (NJWG), which promulgated a series of recommendations, including minimum standards for administering voluntary state herd JD status programs. NJWG also has developed educational programs to increase awareness among producers and an accreditation program for laboratories that test for JD. Despite significant strides, the lack of perceived priority or cost by the industry and veterinary profession, lack of market incentives, and lack of a nationally coordinated effort and supporting infrastructure have resulted in haphazard implementation of some of NJWG’s important recommendations.
In recent decades, there has been growing concern over the lack of effective JD control; the apparent increase in global prevalence; and the implications for accompanying animal health, economies, and trade. The recognition that the Map host range includes ruminant and nonruminant wildlife also is alarming. The spread of JD from domesticated animals to wildlife could significantly alter some wildlife populations, and the development of wildlife reservoirs could hamper the ability to control or eradicate JD in domesticated livestock. Finally, there is increasing concern over the human health implications of JD in livestock. Although considerable controversy surrounds this issue, there is some evidence that Map plays a role in some cases of Crohn’s disease in humans. There also is concern that Map is becoming more widespread in the environment and in the food chain (possibly through milk and meat), resulting in greater risk of human exposure. If Map were determined to be a human pathogen, JD would be transformed from an animal health and economic issue into a serious public health concern.