The pathogenesis of experimental endo-bronchial Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula)

Aim. To study the nature and development of experimentally induced respirat ory tuberculosis in possums and compare the lesions observed with those see n in the natural disease. Methods. Thirty-three adult possums were inoculated via the endo-bronchial route with 20-100 colony forming units of Mycobacterium bovis. The possums were killed at 1, 2, 3 and 4 weeks after inoculation and the nature and dis tribution of the lesions studied in detail histopathologically. Alveolar ma crophages recovered from the infected possums were also studied ultrastruct urally. Results. Macroscopic lesions were largely confined to the respiratory tract , increasing in size and number with time. Histology greatly increased the detection of the total number of lesions. The most common sites affected ou tside the respiratory tract were the liver and hepatic lymph nodes, but les ions were less common in peripheral lymph nodes than is observed in the nat ural disease. Intra-pulmonary lesions were centred on blood vessels and the ir associated lymphatics. Peripheral blood lymphocyte blastogenic responses to M. bovis antigens were first detected at 3 weeks after inoculation, whi ch was 1 week after lymphocyte infiltrations were detected in the lungs, bu t 1 week before the majority of infections became generalised. Conclusions. Differences in the nature of pulmonary lesions and the distrib ution of lesions were observed between experimentally induced and the natur al disease. Rapid haematogenous and lymphatic spread occurs early in the ex perimentally induced disease.