A rabbit model for study of Mycobacterium paratuberculosis infection

Of 21 newborn rabbits inoculated orally with Mycobacterium paratuberculosis ATCC 19698, 13 (62%) became infected, as determined by histopathology and culture. Of the 21 inoculated rabbits, 14 (67%) experienced episodes of intermittent diarrhea, sometimes as early as 5 months after inoculation. Feces varied in consistency from soft-semisolid to watery. The organism was isolated from the sacculus rotundus, vermiform appendix of the cecum, ileum, mesenteric lymph node, and feces of 9 of 21 (43%) M. paratuberculosis-inoculated rabbits 8 to 10 months after inoculation. One infected rabbit gradually became severely emaciated; advanced paratuberculosis was confirmed by culture and histopathology. Of 21 rabbits, 9 (43%) developed multifocal, well-demarcated granulomatous enteritis in the sacculus rotundus and the vermiform appendix of the cecum. There was no significant difference in the rate of infection when the organisms were administered daily for 5 or 10 days in cow milk or broth. There was no discernible effect of pregnancy, parturition, or lactation on the severity of intestinal lesions, clinical signs, or the number of rabbits infected. Complement fixation and delayed-type hypersensitivity skin tests failed to detect infection. The results of this study suggest that newborn rabbits inoculated orally with M. paratuberculosis constitute a useful animal model for the study of paratuberculosis infection.