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

To study the nature and development of experimentally induced respiratory tuberculosis in possums and compare the lesions observed with those seen in the natural disease.

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 distribution of the lesions studied in detail histopathologically. Alveolar macrophages recovered from the infected possums were also studied ultrastructurally.

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 outside the respiratory tract were the liver and hepatic lymph nodes, but lesions were less common in peripheral lymph nodes than is observed in the natural disease. Intra-pulmonary lesions were centred on blood vessels and their associated lymphatics. Peripheral blood lymphocyte blastogenic responses to M. bovis antigens were first detected at 3 weeks after inoculation, which was 1 week after lymphocyte infiltrations were detected in the lungs, but 1 week before the majority of infections became generalised.

Differences in the nature of pulmonary lesions and the distribution of lesions were observed between experimentally induced and the natural disease. Rapid haematogenous and lymphatic spread occurs early in the experimentally induced disease.