JD is characterized by vague and often variable clinical signs, and the clinical signs and the severity of gross and histological lesions do not always correspond (Allen et al., 1968; Downham, 1950; Hallman and Witter, 1933; Macindoe, 1950; Smyth, 1935; Smyth and Christie, 1950). Whitlock and Buergelt (1996) have described the following progression of disease in cattle (summarized in Table 2–2).

In Stage I, animals typically exhibit no overt evidence of infection with Mycobacterium avium subsp. paratuberculosis (Map). Stage I JD is typically found in calves and heifers, most immature young stock, and many adult cattle. No routine or special clinicopathologic tests or serology will detect disease in these animals. Only postmortum tissue culture or, less often, histopathology can detect infection at this early stage of disease.

Most animals in Stage II JD are adults that are carriers of Map. The animals do not exhibit clinical signs typical of JD, but they sometimes have detectable antibodies or exhibit altered cellular immune responses. Many are fecal-culture negative, although they intermittently shed low numbers of organisms in feces. In a small percentage (15–25 percent), disease can be detected by fecal culture, by altered cellular immune response, by serum antibodies, or by histopathology. An unknown proportion of Stage II animals progress slowly to Stage III (clinical disease), but because so many are culled

Front Matter (R1-R14)

Executive Summary (1-12)

1. Introduction (13-15)

2. Johne's Disease in Domesticated and Wild Animals (16-44)

3. Diagnostics (45-65)

4. Control Principles and Programs (66-98)

5. Economic Implications of Johne's Disease (99-103)

6. Johne's Disease and Crohn's Disease (104-120)

7. Conclusions and Recommendations (121-132)

References (133-174)

Appendix A: Interpretation of Diagnostic Results (175-178)

Appendix B: USAHA Voluntary Johne's Disease Herd Status Program for Cattle (179-193)

Appendix C: USDA/APHIS Draft Johne's Disease Control Program (194-220)

About the Authors (221-225)

Board on Agriculture and Natural Resources Publications (226-229)