Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 1996
Publication Date: N/A
Interpretive Summary: Bovine tuberculosis has almost been eliminated from the United States because of the success of eradication programs, which were started in 1917. The primary method currently used for detecting cattle with tuberculosis is inspection of carcasses when cattle are slaughtered. In order for diseased cattle to be identified, they must have visible signs of tuberculosis that can be detected by meat inspectors. In this study, we determined that not all cattle with tuberculosis have evidence of disease that would be detected when carcasses are inspected. Some of the cattle with tuberculosis were detected only after laboratory examination of tissue samples collected at slaughter. These findings indicate that not all cattle with tuberculosis can be detected using only inspection of carcasses at slaughter. Other methods need to be used in conjunction with meat inspection to identify all cattle with tuberculosis so that the disease can nbe eradicated from the United States. Eradication of bovine tuberculosis is important because of public health and trade issues.
Technical Abstract: Detailed post mortem examinations were conducted on 30 cattle from a dairy herd with bovine tuberculosis to determine the distribution of lesions in Mycobacterium bovis-infected cattle. Twenty-four different tissue specimens from each animal were examined for gross lesions and collected for bacteriologic culturing and histologic examination. Tuberculosis was confirmed in 15 cattle with evidence of infection in one or more of the following tissues: medial retropharyngeal, parotid, tracheobronchial, mediastinal, caudal deep cervical, and subiliac lymph nodes; palatine tonsil; and lung. Gross and histologic lesions were present most frequently in lymph nodes of the thoracic region. Mycobacterium bovis was isolated from three cattle that had no gross lesions of tuberculosis. One animal had lesions only in the subiliac lymph node, which is not routinely examined during slaughter surveillance. Results of this study indicate that not all cattle infected with M. bovis have visible lesions of tuberculosis in sites that are routinely inspected. These findings are important because detection of gross lesions of tuberculosis during inspection of carcasses at slaughter is the primary method for detection of tuberculous cattle and herds in the United States.