Difficulties in diagnosis of bovine tuberculosis in suggestive lesions

Abstract

The bovine tuberculosis is a zoonotic disease with importance to the public health. The post mortem identification and its fast and accurate diagnosis combined with the epidemiology knowledge are essential to fight against the advance of this disease. Therefore, the present study aimed to perform the diagnosis of Mycobacterium bovis, by molecular detection and also by histopathologic lesion characterization and identification of acid-fast bacilli (AFB), seeking to compare them. During slaughter of cattle in slaughter plants, under Federal Inspection Service in São Paulo State, were collected and identified, in duplicate, tissue samples with suggestive lesions of tuberculosis. One of the samples was intended for histopathology, being performed the hematoxylin-eosin (HE) staining for lesion characterization and the Ziehl-Neelsen (ZN) staining to identification the AFB. The other sample was separated to the molecular diagnosis, Polymerase Chain Reaction (PCR) and nested PCR. The bacterial DNA present in the lesion was extracted and the PCR was performed, showing 20.84% (10/48) of positive samples. However, when the results were compared with more sensitive tests (nested PCR) and cheapest ones (histopathologycal characterization of lesions and the AFB identification), different results were found. When performing nested PCR in negative samples by conventional PCR (38/48), it was found more 18.74% (9/38) of positive samples resulting in 39.58% (19/48) of positive samples by molecular diagnosis from tissue lesions. However, histopathological characterization by hematoxylin-eosin resulted in 66.67% (32/48) of positive samples and the identification of AFB by Ziehl-Neelsen, 54.17% (26/48) of positive samples for bovine tuberculosis. The molecular tissue diagnosis from lesions is possible, but it should not be the only method used for bovine tuberculosis diagnosis.