Diagnosis and Control of Johne's Disease (2003)Board on Agriculture and Natural Resources
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Johne's Disease is a chronic, progressive intestinal disease caused by infection with Mycobacterium avium subspecies paratuberculosis (Map) that affects primarily ruminant animals. In recent decades there has been growing concern over the lack of effective control of this disease and questions have arisen regarding the possibility that Map infection could be a cause of some cases of Crohn's disease in humans. This report presents a broad outline of the steps that should be taken to control Johne's disease, reduce the spread of Map, and minimize effects of the disease in animals. The report also describes the weaknesses of our current research agenda and provides recommendations for a new research strategy to resolve the question of whether there is a link between Johne's and Crohn's diseases.
- Prevention of fecal contamination of feed, water, and the environment will reduce the opportunity for transmission of Map.
- Animal agriculture has recognized the serious economic consequences of the disease and identified it as a major animal health issue. U.S. animal agriculture has requested assistance addressing JD.
- Animals in the late preclinical or clinical stage of infection are more likely to shed high numbers of organisms than are early-stage infected animals.
- Available diagnostic tests and information about the biology of JD and methods to control it are adequate for immediate implementation of control programs.
- Because JD is currently of greatest concern to the dairy industry much of the emphasis in control recommendations is directed there. Other industries, however, should consider this an opportune time to deal aggressively with the disease, before infection prevalence increases and the disease becomes more widespread.
- Control of JD will require a long-term commitment and iterative program implementation to maximize the chance of success. This commitment must come from all constituencies, including USDA, state agencies, and industry.
- Diagnostic and screening tests are adequate for detecting shedders at the individual animal and herd level, but tests are used best at the herd level.
- Infected adult ruminants are the major transmission source of the organism.
- Introduction of new Map-infected animals is a primary means by which a herd or flock becomes infected.
- JD control programs are based on knowledge about the transmission of Map, the organism's persistence in the environment, and methods for reducing exposure to Map in animal environments.
- Johne's Disease (JD) is a significant animal health problem that warrants implementation of control programs tailored to specific animal species and specific segments of the agriculture industry. Furthermore, JD control deserves high priority from the USDA, individual states, and industry.
- Map can persist in water, manure, or other environmental sites for extended periods (one year or longer).
- Most transmission of Map is through a fecal-oral route, but transmission also can occur in utero or via colostrum or milk.
- Removal of newborn calves from dams at birth (before suckling) can interrupt an important avenue of transmission.
- Reporting ELISA results as likelihood ratios, rather than as a positive or negative test result, will be beneficial for control programs and could increase confidence in the tests.
- The NAHMS prevalence surveys should continue, with attention given to maximizing the data obtained from the samples collected through add-on projects and investigations.
- The USDA National Animal Health Monitoring System (NAHMS) prevalence surveys for JD have been a critical element in laying the groundwork for control programs.
- The Voluntary Bovine Johne's Disease Control Program proposed by the National Johne's Working Group (NJWG) has most of the elements necessary for a successful control program, but prospects for success are and will be limited by a lack of uniform implementation among individual states.
- The committee considered ongoing research to be important for the success of any control program and therefore felt that a research element should be integral to future program development.
- The committee endorses the NWJG's efforts in educating producers and veterinarians, and advocates the expansion of these efforts.
- The committee identified significant gaps in the current state of knowledge of the pathophysiology, immunology, diagnosis, and control of JD in domesticated livestock and wildlife.
- The emergence of regional and national JD programs in Australia, Japan, and parts of Europe to certify the JD status of herds, flocks, and zones will increase pressure for additional government assurances of the JD status of animals and animal products destined for export.
- There are significant gaps in knowledge about some areas relevant to control, and are discussed below under recommendations. The committee emphasizes that closing those gaps will improve control programs, although the need for information should not delay their implementation.
- There is some evidence that JD could be linked to Crohn's disease in humans.
- There remains insufficient evidence to prove or disprove that Mycobacterium avium subsp. paratuberculosis is a cause of some or all cases of Crohn's disease (CD) in humans.
- Young animals (less than 6 months of age) are most susceptible, but older animals can be infected by heavy or prolonged exposure