[Role of atypical mycobacteria in the occurrence of nonspecific tuberculin reactions in cattle].

Bacteriologic investigations were carried out with a total of 295 cattle of the Holstein-Zebu breed that responded positively to tuberculin. Mycobacterium bovis was isolated from 66 animals, and 12 species of atypical mycobacteria were isolated from 94 animals. Parallel studies were comparatively made of the intradermal reaction test and the bacterial findings. Three groups of calves were infected with various atypical mycobacteria, and their response was followed up with the use of the avian and the bovine type of tuberculin on the 100 th day of infection. It was found that the unspecific tuberculin response of cattle in Cuba were not uncommon, and the best proportion of such reactions were shown to be due to the involvement of atypical mycobacteria. The investigated cattle with a positive response to bovine tuberculin at a single intradermal test were harbouring M. bovis in 66 cases (22.3 per cent), atypical mycobacteria in 94 cases (32.1 per cent), and Actinomyces bovis in 7 cases (2.3 per cent). In 128 of the cases (43.3 per cent) both the morphologic and the bacteriologic findings were negative. The cases with a stronger response at the single intradermal tuberculin test in which the skin fold enlarged over 6.5 mm corresponded to a larger extent to the actual specific infection in the animals than to an infection caused by atypical mycobacteria, however, this could not be absolutely stated for all animals. Following a muscular as well as an oral infection of calves with atypical mycobacteria the allergic response was enhanced from the 40 th up to the 100 th day, the positive reaction to avian tuberculin becoming stronger than to bovine tuberculin.(ABSTRACT TRUNCATED AT 250 WORDS)