Abstract

An 11-year-old female bontebok, Damaliscus pygargus dorcas, was euthanatized due to clinical evidence of lethargy, anorexia, interstitial pneumonia, and inability to rise from a sternal position after immobilization. At necropsy, miliary granulomatous lesions measuring 3–10 mm in diameter were present in the liver, kidneys, spleen, lungs, pleural surfaces, and multiple thoracic and abdominal lymph nodes. Granulomas were also found in the bones of the 4th and 5th lumbar vertebrae causing spinal cord compression. Cytologic examination of touch impressions from the granulomas revealed acid-fast staining material interpreted as Mycobacterium sp. organisms. Another bontebok (a 6-year-old female) in direct contact with the aforementioned case was euthanatized due to concerns about mycobacterial disease and the fact that the animal needed multiple immobilizations to treat a recently diagnosed lameness. At necropsy, miliary granulomatous lesions similar to those seen in the other bontebok were found in the liver, spleen, kidneys, lung, pleural surfaces, and multiple lymph nodes.

Histopathologic examination in both cases confirmed the presence of systemic granulomatous inflammation. Fites-Furaco acid-fast staining of the formalin fixed tissues revealed acid-fast positive bacteria that were extremely rare (estimated one bacteria per 20 granulomas examined; fewer than five bacteria seen in an entire section of lung). The bacteria were present in the cytoplasm of multi-nucleated giant cells, were filamentous in shape, and measured approximately 10–12 µm in length. Samples of lymph node and lung from both cases were submitted to the National Veterinary Services Laboratories in Ames, IA for mycobacterial culture and PCR. PCR testing on the formalin fixed tissues was negative using primers for M. tuberculosis-complex species, M. avium species, and M. avium subspecies paratuberculosis. Culture of lung and lymph nodes from both animals using standard mycobacterial isolation techniques yielded Mycobacterium kansasii.

These cases were challenging in that both the gross and microscopic lesions in the bontebok were suggestive of M. bovis infection, however it was felt that the filamentous acid-fast bacteria were significantly longer than the typical morphology of M. bovis. The possibility of M. bovis infection raised significant management and regulatory concerns until the final culture results were received 8 weeks after the first necropsy. M. kansasii is an atypical mycobacterial organism that can cause tuberculosis-like disease in a variety of species.^1-3

Literature Cited

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3.  Koirala, J. 2009. Mycobacterium kansasii, http://emedicine.medscape.com/article/223230-overview.