Abstract
Tuberculosis has become an important disease in captive elephants, particularly Asian elephants (Elephas maximus). Diagnosing tuberculosis in elephants has been problematic as many tests have inadequate sensitivity or specificity.2-4 A multiple-antigen enzyme-linked immunosorbent assay (ELISA) was previously investigated for detecting infection in Asian elephants and African elephants (Loxodonta africana); this test had excellent sensitivity and specificity but needed further evaluation.1
Modifications to the multiple-antigen ELISA panel have since been made. Valuable antigens were retained, other antigens were removed, and new ones were added. This modified ELISA was re-evaluated, using serum from 68 Asian elephants. Sixteen had M. tuberculosis-positive trunk cultures, while 52 were either culture negative at necropsy or had a history of negative trunk cultures and no contact with infected elephants. Seven elephants were evaluated over time.
The test was 100% (95% CI; 95–100%) specific and 94% (95% CI; 79–100%) sensitive using two of the six antigens (M. bovis strain AN5 culture filtrate and M. tuberculosis early secretory antigenic target 6). “Effectively-treated” elephants had decreasing seroreactivity, but those that were culture-positive posttreatment were more consistently seroreactive. Although “effectively-treated” elephants had declining seroreactivity, they still usually had higher values than animals that had never been infected.
Serology continues to show great promise in detecting tuberculosis in elephants, often detecting infection months-to-years sooner than trunk wash culture. Advances in techniques may soon make serology even more practical. While serology should not replace trunk wash culture, it is a useful adjunct for early detection of infection in elephants and for monitoring treatment.
Acknowledgments
We thank the many veterinarians, owners, caretakers, and managers of elephant-owning institutions that participated in this investigation, as well as Drs. Michele Miller and Susan Mikota for helping to coordinate sample collection. We also thank Kimberly Deines and other laboratory personnel who processed ELISA samples. The study was partially funded by a grant from USDA, CSREES to Colorado State University Program of Economically Important Infectious Animal Diseases.
Literature Cited
1. Larsen, R.S., M.D. Salman, S.K. Mikota, R. Isaza, R.J. Montali, and J. Triantis. 2000. Evaluation of a multiple-antigen enzyme-linked immunosorbent assay for detection of Mycobacterium tuberculosis in captive elephants. J Zoo Wildl Med. 31:291–302.
2. Mikota, S.K., L. Peddie, J. Peddie, R. Isaza, F. Dunker, G. West, W. Lindsay, R.S. Larsen, M.D. Salman, D. Chatterjee, J. Payeur, D. Whipple, C. Thoen, D.S. Davis, R.J. Montali and J. Maslow. 2001. Epidemiology and diagnosis of Mycobacterium tuberculosis in six groups of elephants. J Zoo Wildl Med. 32:1–16.
3. Mikota, S.K., R.S. Larsen, and R.J. Montali. 2000. Tuberculosis in elephants in North America. Zoo Biol. 19:393–403.
4. U.S. Department of Agriculture. 2003. Guidelines for the control of tuberculosis in elephants. Animal and Plant Health Inspection Service; Animal Care. Washington, DC. http://www.aphis.usda.gov/ac/TBGuidelines2003.pdf. (VIN editor: Link not accessible 1/27/21).