Evaluation of Diagnostic Tests for Antemortem Tuberculosis Screening in Captive Sloth Bears (Melurus ursinus)
Confirmatory antemortem diagnosis of tuberculosis in wild animals remains a difficult proposition for zoo veterinarians.2 As in the case of many other wild species, there is critical lack of accredited tests for tuberculosis screening in sloth bears (Melursus ursinus). Isolation and identification of the Mycobacterium tuberculosis/bovis by culture is the gold standard for tuberculosis diagnosis in any species. Methods utilizing cell-mediated immune response as well as humoral antibody response have been tried in several wild species. However, the diagnostic sensitivity and specificity of these antemortem tests, accredited for use in humans, are unknown in wild species. We evaluated various available techniques and methods for antemortem tuberculosis screening in 14 sloth bears. During postmortem examination, M. tuberculosis was isolated and identified by culture from the 14 carcasses, in nodules in lung parenchyma. The culture results were compared with antemortem test results (chest radiography, routine blood analysis,3 tuberculin skin test, acid-fast staining of tracheal smears, culture and nucleic acid amplification of lung wash, QuantiFERON-TB Gold®, STAT-PAK® and DPP Vet Assay®). None of the antemortem tests gave positive results in all the 14 cases, but some tests seem to show better correlation with culture than others. Tuberculosis in captive sloth bears represents a typical case of spillover infection resulting from human cohabitation.1 Ascertaining the diagnostic sensitivity and specificity of the various antemortem tuberculosis screening tests will help in the early diagnosis and treatment monitoring of this chronic disease in this endangered species.
1. Bourne DC, JM Cracknell, HJ Bacon. Veterinary issues related to bears (Ursidae). Int Zoo Yearb. 2010;44(1):16–32.
2. De Lisle GW, Bengis RG, Schmitt SM, O’Brien DJ. Tuberculosis in free-ranging wildlife: detection, diagnosis and management. Rev Sci Tech. 2002;21(2):317–334.
3. Shanmugam AA, et al. Hematology of sloth bears (Melursus ursinus ursinus) from two locations in India. J Wildl Dis. 2008;44(2):509–518.