Systemic but not intra-intestinal vaccination with BCG reduces the severity of tuberculosis infection in ferrets (Mustela furo).

SETTING: Ferrets are important wildlife vectors of bovine tuberculosis (Mycobacterium bovis) in New Zealand. By reducing the severity and/or incidence of tuberculosis (TB) in wild ferret populations, vaccination may limit disease transmission to livestock.
OBJECTIVE: To investigate whether vaccination of ferrets with attenuated M. bovis BCG via systemic or intraintestinal routes can reduce the severity of TB resulting from oral M. bovis challenge.
DESIGN: Groups of captive ferrets were vaccinated with live BCG via sub-cutaneous injection or intra-duodenal inoculation, twice, 4 weeks apart. Vaccinated and non-vaccinated (control) ferrets were subsequently challenged orally with virulent M. bovis to simulate the natural route of infection. Peripheral blood lymphocyte reactivity was longitudinally monitored, and the outcome of challenge was determined 20 weeks later by autopsy, histology and bacteriological culture. RESULT: Both vaccination routes induced tuberculin-specific lymphocyte reactivity; however, only the subcutaneous route was effective in reducing disease. Subcutaneous vaccinated ferrets had a lower severity of infection than non-vaccinated control animals, as indicated by significant reductions in viable bacterial burdens and prevention of gross lesions in mesenteric lymph nodes (the primary site of infection), and a lower incidence of bacterial translocation to thoracic lymph nodes. However, sub-cutaneous vaccination did not reduce the incidence of mesenteric lymph node infection.
CONCLUSIONS: Systemic vaccination with BCG can reduce the severity of TB resulting from oral challenge with virulent M. bovis; however, delivery of viable BCG to the upper intestinal tract may not protect ferrets against TB.