Histopathological and Molecular Investigation of Natural Cases of Bovine Tuberculosis Infection in Cattle

ABSTRACT

Bovine tuberculosis (bTB), a chronic infection in cattle caused by Mycobacterium tuberculosis/bovis, that impacts productivity and represents a major public health threat. Although the considerable economic costs and zoonotic risk consequences associated with the disease, accurate estimates of bTB prevalence are lacking in many countries, including India. Therefore, in the current study for collection of tubercular lesions the postmortem examination of 100 cattle was conducted. All major viscera and regional lymph nodes were examined and incised. Histopathology was performed in the cases where gross lesions were suggestive of tuberculosis. PCR was performed on the tissue and faecal samples by using IS6110 insertion sequence, Mycobacterium tuberculosis/bovis complex PCR kit. In 12 animals, nodular lesions with casseating mass suggestive of tuberculosis were observed in the lung tissue. All the 12 lung impression smear and only five faecal smear showed acid fast bacilli stained by Ziehl-Neelsen staining. Histologic features comprised a classic granuloma as a characteristic lesion of tuberculosis composed of a central caseous necrosis with mantle of macrophages, lymphocytes, plasma cells, epithelioid macrophages and Langhan’s giant cells and were observed in all 12 cases. All the tissue samples and 11 faecal samples were positive for the Mycobacterium tuberculosis complex using IS6110 sequence. 8 tissue samples and 4 faecal samples were positive by using Mycobacterium tuberculosis/bovis complex PCR kit. It can be concluded that there was good agreement between histopathology, acid fast staining and PCR. It can also be concluded that faecal samples which are easier to collect should be preferred for diagnosis of TB by PCR in cattle