EARLY LESION FORMATION IN CATTLE EXPERIMENTALLY INFECTED WITH MYCOBACTERIUM-BOVIS

Early lesion formation was examined in 13 calves inoculated intranasal ly with 2 x 10(7) colony-forming units of Mycobacterium bovis and kill ed either singly or in pairs at intervals of less than or equal to 7 d ays from post-inoculation day (pid) 3 to pid 42. Immunological examina tions were carried out before and after infection, and sequential necr opsies were performed. M. bovis was recovered as early as pid 3, from the upper respiratory tract mucosae, retropharyngeal lymph nodes and c audal lung lobe. Gross tuberculous lesions were detected in both the u pper respiratory tract mucosae and in the lungs of the calves killed f rom pid 14 onwards. Lesions were also present in the lymph nodes drain ing these areas. On histological examination, neutrophils appeared to play a key role in the earliest stages of lesion formation, and lesion mineralization was observed for the first time at pid 35. The contemp oraneous development of lesions and cellular immunity, as demonstrated by in-vitro lymphocyte proliferation and interferon-gamma assay respo nses, provided further evidence of the role of immunopathogenic mechan isms in the development of bovine tuberculosis. (C) 1998 W.B. Saunders Company Limited.