Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/4/1997
Publication Date: N/A
Citation: Interpretive Summary: Recently a new, rapid test for diagnosis of tuberculosis (TB) was developed in our laboratory. The method, which is based on the polymerase chain reaction (PCR) technology for amplification of DNA, can identify the tuberculosis-causing organisms in 2 to 3 days, whereas identification by standard culture methods requires 2 to 3 months. This paper describes how the PCR test was used to diagnose tuberculosis in 2 snow leopards at a zoological park in Oklahoma. Although TB had not been suspected as the cause of death, pathologists recognized that lesions in the lung were suspicious for this disease and subsequently special staining procedures were used to show that the tissues contained mycobacteria, the type of organism that causes TB. Because there are many different types of mycobacteria, however, a definite diagnosis could not be made until the organisms were specifically identified. The new PCR test was applied to the tissues submitted for histopathologic examination and the result showe the organisms belonged to the group known to cause TB in many animal species. Later, frozen tissue from one of the leopards was submitted for culture and Mycobacterium bovis was isolated by bacteriologic culture, thus confirming the PCR result. This study illustrates the usefulness of a PCR test for rapid diagnosis of TB, which is important in situations such as this because of the public health issues which result from exposure of human beings to infected animals.
Technical Abstract: Two related snow leopards, housed in the same exhibit in the Tulsa Zoological Park, developed a fatal chronic respiratory disease. At necropsy, both animals had severe and extensive bilateral pneumonia, characterized grossly by numerous individual to coalescing grayish-tan nodules distributed throughout almost all lung lobes. There were also regions of cavitation, sometimes extensive. Microscopically, the lesions were granulomatous with few giant cells and marked necrosis with resulting cavitation, but no calcification. Lung sections stained for acid fast bacteria with the Ziehl-Neelsen method demonstrated rare, uniform- sized, plump, rod-shaped bacteria that occurred individually or in pairs within macrophages. PCR was utilized to test for mycobacterial DNA in the formalin-fixed, paraffin-embedded tissues used for histopathology. Three separate primer pairs were used. IS6110 for organisms in the M. tuberculosis complex (M. tuberculosis, M. bovis, M. microti, M. africanum); IS900 for M. paratuberculosis and IS1245 for the M. avium complex. Tissues were positive with the IS6110 primer only. Subsequently, frozen lung tissue from one of the leopards was found and submitted for culture; M. bovis was isolated from that sample. In these two cases, where fresh tissue was not initially available for culture and identification, the PCR technique proved to be a rapid and accurate diagnostic tool for identifying M. bovis in the diseased leopards.