The pathology of tuberculosis, caused by mycobacterium tuberculosis, in a herd of semi free-ranging springbok (Antidorcas marsupialis)

Abstract

This first detailed description of the pathology of tuberculosis, caused by Mycobacterium tuberculosis in springbok is reported. The springbok were part of a semi free-ranging herd kept on the grounds of iThemba Laboratory for Accelerator Based Science (LABS) in the Kuils River district of the Western Cape Province, South Africa. Of the 33 animals sampled, two animals had tuberculosis lesions. Mycobacterium tuberculosis was isolated from these two animals, as well as an animal that did not show tuberculosis pathology. The index case was an adult ewe that was presented for necropsy in a severely weakened condition. The ewe showed advanced miliary tuberculosis with marked macroscopic lesions in the lungs, pleura and respiratory lymph nodes. Limited sampling was done but microscopic tuberculosis lesions were found in almost all the organs sampled, and acid-fast bacilli were generally numerous. Six healthy rams were culled nine months later and a pilot study indicated miliary tuberculosis lesions in one ram, which again were macroscopically most prominent in the lungs, pleura and respiratory lymph nodes. Macroscopic lesions were also noted in the sternal, iliac, prefemoral and retropharyngeal lymph nodes. Microscopy in this animal revealed lesions in the macroscopically affected organs as well as numerous other lymph nodes, and suspected lesions occurred in the testicle and colon. Acid-fast bacilli were scarce to moderate in affected organs. Because of the miliary nature of the lesions in both affected animals, the route of infection could not be established conclusively. The lesions in most affected organs of both animals resembled classical tuberculous granulomas, viz. central caseous necrosis, with various degrees of calcification, surrounded by various numbers macrophages, epithelioid cells, multinucleated giant cells and lymphoplasmacells, and mild to moderate fibrous encapsulation. Necrotic lesions in the spleen, liver and kidney of the ewe were more disseminate and coagulative. A main study conducted on healthy culled animals 19 months after the pilot study failed to find any animal with tuberculosis lesions in the group of 25 sampled. These animals were all negative for mycobacteria via mycobacterial culture. The Interferon-gamma (INFg) assay was performed on all the animals of the pilot and main study but failed to identify the culture-positive animals and showed one false-positive reaction.