Swine tuberculosis in South Dakota

Area of Science:

• Veterinary Pathology
• Bacteriology
• Food Safety

Background:

• Granulomatous lesions in bovine lymph nodes are a concern for meat inspection.
• Mycobacterial infections, particularly Mycobacterium avium complex, are prevalent in cattle.

Purpose of the Study:

• To determine the prevalence and types of mycobacteria in granulomatous lymph node lesions from cattle in South Dakota.
• To compare mycobacterial isolation rates with microscopic identification of acid-fast bacilli and the occurrence of granulomatous lesions.

Main Methods:

• Sampling of 200 lymph node lesions identified as granulomatous by meat inspectors at four South Dakota abattoirs.
• Bacteriological isolation and identification of mycobacteria from lesion samples.
• Microscopic examination for acid-fast bacilli.

Main Results:

• Mycobacteria were isolated from 195 (97.5%) of 200 lesions.
• Mycobacterium avium serotypes 1 and 2 constituted 89% of all mycobacterial isolates.
• Mycobacterial isolation was significantly more frequent than microscopic observation of acid-fast bacilli (P < 0.001).
• Isolation frequency closely matched the occurrence of granulomatous lesions.

Conclusions:

• Mycobacterium avium serotypes 1 and 2 are the primary mycobacteria associated with granulomatous lymph node lesions in cattle in this region.
• Bacteriological isolation of mycobacteria is a more sensitive method for detecting infection than microscopic examination.
• The presence of granulomatous lesions is a strong indicator of mycobacterial infection in cattle.