Aerosol delivery of virulent Mycobacterium bovis to cattle.

SETTING Although animal models of aerosol inoculation of Mycobacterium tuberculosis and M. bovis have been reported using laboratory animals, a model of aerosol delivery of M. bovis to cattle has not been reported previously. OBJECTIVE Develop and characterize a model of aerosol delivery of M. bovis to cattle, and compare the distribution of lesions in cattle infected with either of two different strains of M. bovis, one isolated from cattle (HC2005T), and the other isolated from white-tailed deer (1315). DESIGN Cattle (n=20, female and castrated males) aged 4 months, were infected with 1 x 10(3) (n=5) or 1 x 10(5) (n=5) colony-forming units (CFU) of M. bovis 1315 or 1 x 10(3) (n=5) or 1x10(5) (n=5) CFU of M. bovis HC2005T. Calves were infected using a commercially available aerosol delivery system. One hundred fifty-five days after infection, calves were euthanized, examined and tissues collected for microscopic analysis and bacteriologic culture. RESULTS Nineteen of 20 calves developed tuberculosis. Typical tuberculous lesions were most pronounced in the lungs and tracheobronchial and mediastinal lymph nodes. CONCLUSION The system described provides a reliable method of aerosol delivery of M. bovis to cattle. Lesion distribution suggests that the aerosolized inoculum was delivered deep into pulmonary alveoli and thus represents true aerosol exposure. Disease was more severe in groups receiving the highest dose of either inoculum strain; however, differences between strains were not seen. Published by Elsevier Science Ltd.