Case report and DNA characterization of Mycobacterium avium isolates from multiple animals with lesions in a beef cattle herd.

Abstract

The Mycobacterium avium complex includes the closely related species M. avium, M. intracellulare,and M. paratuberculosis. In animals, M. paratuberculosis is undoubtedly the most important member of the M. avium complex as far as economic losses due to reduced production and morbidity are concerned. However, other members of the M. avium complex also cause veterinary problems by infecting a wide range of different mammalian hosts, including pigs, farmed deer, and cattle. Members of the M. avium complex apart from M. paratuberculosiscan cause lesions in cattle that are grossly and microscopically indistinguishable from those caused by Mycobacterium bovis. 2 Infection with members of this complex, including M. paratuberculosis, can also cause cattle to respond to bovine tuberculin in a skin test. Evidence from the use of avian tuberculins in comparative skin tests suggests that in some areas, there is a high prevalence of infection in cattle. 7 However, many of these animals do not have visible lesions on necropsy, and it is rare to find generalized infections causing clinical disease by members of the complex other than M. paratuberculosis. The epidemiology of infections in cattle caused by members of the M. avium complex other than M. paratuberculosis has not been well defined. While members of this complex have been isolated not only from birds, but also from a wide range of environmental sites, including soil and water, 5 the source of M. avium complex infections in cattle has rarely been established. 1 The advent of DNA typing methods offers new tools to investigate the epidemiology of infections caused by this group of organisms. A compulsory control scheme for bovine tuberculosis has been in effect in New Zealand for over 25 years. 10 This scheme has been very successful in eradicating M. bovis from cattle herds in all areas of the country except where there are reservoirs of infection in wildlife. As part of the control scheme, all animals are carefully examined at slaughter for the presence of lesions resembling bovine tuberculosis. Samples from suspect cases are taken for histologic and bacteriologic confirmation of the macroscopic findings. Bacteriological examinations have shown a low prevalence of tuberculous lesions caused by the M. avium complex (Table 1). Apart from the episode described in this paper, no cattle herds were found in New Zealand in 1994 or 1995 that contained more than 3 animals with lesions caused by the M. avium complex. In 1992, M. bovis was isolated from 10 animals from a beef herd in the Hawkes Bay region of New Zealand. The