Oral infection of ferrets with virulent Mycobacterium bovis or Mycobacterium avium: susceptibility, pathogenesis and immune response.

Ferrets are important wildlife reservoirs of tuberculosis in New Zealand, where they acquire infection primarily through scavenging infected carrion. In the present study, groups of laboratory-reared ferrets were infected orally with 5 x 10(6)colony-forming units of Mycobacterium bovis or Mycobacterium avium. Body weight and tuberculin-specific immune reactivity were monitored at intervals (pre-infection, and 4 and 20 weeks post-infection) and animals were killed at 20 weeks post-infection for post-mortem, histopathological and bacteriological examinations. Weight loss was significantly greater in M. bovis -infected than in M. avium -infected ferrets. M. bovis, unlike M. avium, sometimes produced gross necrotic lesions in the mesenteric lymph nodes. M. bovis invariably produced microscopical foci of mycobacterial infection or tissue necrosis typical of tuberculosis, whereas M. avium did so in only one of nine animals. Mycobacteria were recovered from the lymphatic tissues of all M. bovis -infected ferrets but from only five of nine M. avium -infected animals; and the mean bacterial burdens of the lymph nodes of the head and intestinal regions were > 10-fold and > 100-fold greater, respectively, for M. bovis -infected than for M. avium -infected animals. M. bovis, unlike M. avium, evoked tuberculin-specific peripheral blood lymphocyte reactivity and serum antibody responses.