Agreement between PCR and conventional methods for diagnosis of bovine tuberculosis

Abstract

DIAGNOSIS OF BOVINE TUBERCULOSIS (TB) WAS ANALYZED USING POLYMERASE CHAIN REACTION (PCR) IN 2 GROUPS OF ANIMALS: THE FIRST FORMED BY 21 TUBERCULIN REACTING CATTLE FROM A TB ENDEMIC ZONE, AND THE SECOND BY 20 TUBERCULIN NEGATIVE CATTLE FROM A TB-FREE ZONE. ALL 41 ANIMALS WERE SACRIFICED AND POST MORTEM INSPECTION, HISTOPATHOLOGY AND MYCOBACTERIUM BOVIS CULTURE WERE PERFORMED. IN THE FIRST GROUP, TUBERCULOUSLIKE LESIONS WERE FOUND IN ALL 21 CASES BY HISTOPATHOLOGY (HEMATOXYLIN-EOSIN), 15 OF THEM HAD COMPATIBLE LESIONS (ZIEHL-NEELSEN POSITIVES) AND M. BOVIS WAS CULTURED ONLY IN 11. LESIONS WERE NOT FOUND IN ANY OF THE ANIMALS FROM THE SECOND GROUP. HISTOPATHOLOGY SHOWED GOOD CONCORDANCE WITH CULTURE, BOTH FOR TUBERCULOSIS-LIKE LESIONS (COHEN´S KAPPA VALUE, K = 0.52) AS WELL AS FOR COMPATIBLE LESIONS (K = 0.44). DNA WAS OBTAINED FROM LYMPHATIC NODES ASSOCIATED TO THE RESPIRATORY TRACT IN ALL 41 CASES. A SIMPLE PCR DIRECTED TOWARDS THE GENE OF THE MPB70 PROTEIN WAS IMPLEMENTED AND A NEW NESTED PCR WAS DEVELOPED. THE NESTED PCR DETECTED AS POSITIVES THE 21 CASES WITH TUBERCULOUS-LIKE LESIONS (100%). BOTH PCR METHODS SHOWED GOOD CONCORDANCE WITH HISTOPATHOLOGY (K = 0.44-0.71), BUT IN THE CASE OF M. BOVIS CULTURE THIS CONCORDANCE WAS OBSERVED ONLY WITH NESTED PCR (K = 0.52). CONSIDERING THE COMPATIBLE LESIONS (ZN) AS A CONFIRMATIVE DIAGNOSIS, BOTH CULTURE AND SIMPLE PCR SHOWED 53% OF SENSITIVITY AND 88% OF SPECIFICITY, WHILE THE NESTED PCR SHOWED 100% OF SENSITIVITY AND 77% OF SPECIFICITY. THE NESTED PCR CAN ALLOW THE CONFIRMATION OF TB DIAGNOSIS IN 24 HOURS.