Evaluation of Different PCR-based Techniques in Diagnosis of Bovine Tuberculosis in Infected Cattle Lymph Nodes

Bovine tuberculosis is a chronic bacterial disease of animals and humans caused by Mycobacterium bovis. In a large number of countries bovine tuberculosis is a major infectious disease among cattle and other domesticated animals. M. bovis can infect humans, primarily by the ingestion of unpasteurized dairy products but also in aerosols and through breaks in the skin. Raw or undercooked meat can also be a source of the infection. In live cattle, tuberculosis is usually diagnosed in the field with the tuberculin skin test which should be performed in the course of the twelve months prior to presentation for slaughter. An additional problem with the skin test is the widespread cross-reactivity with environmental mycobacteria which can limit its use. The diagnosis is confirmed by the isolation and identification of M. bovis on selective culture media or by different polymerase chain reaction (PCR) assays. In this study, initially, 70 cows with the TB symptoms were screened for tuberculosis infection using intradermal tuberculin test (IDTT). The test results revealed that 17 animals (24%) showed positive reaction. The lymph nodes of positive animals were examined for gross lesions and consequently conducted for bacteriological examination, which revealed that only 12 animals were infected with M. bovis and one animal was infected with pathogenic M. tuberculosis. Therefore, three PCR-based assays (monoplex, conventional multiplex and Real Time PCR) were applied to positive cases. The results revealed that real-time PCR assay was the most sensitive, powerful and efficient assay compared with monoplex and multiplex conventional PCR assays.