Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/11/2008
Publication Date: 7/11/2008
Citation: Waters, W.R., Palmer, M.V., Thacker, T.C., Nonnecke, B.J., Lyashchenko, K., Schiller, I., Marg, B., Oesch, B., Vordermeier, M., O'Brien, D., Schmitt, S., Estes, M. 2008. Tuberculosis Diagnosis: Relevancy of Veterinary Applications to Human Disease [abstract]. p. 17.
Technical Abstract: Veterinary applications of tuberculosis (TB) tests may provide insight into the diagnostic potential and technical development of emerging tests for human TB. Interferon (IFN)-gamma release assays (IGRA) were developed initially for bovine TB eradication programs. As the test relies on functional leukocytes, environmental conditions before and during the in vitro culture period influences the outcome of the test. Effects of stimulation vessel geometry, incubation temperature, and antigen stability at different temperatures were evaluated with blood from experimentally- and naturally-infected cattle. Whole blood was stimulated in 24- (standard), 48- and 96-well culture plates with Mycobacterium bovis PPD, M. avium PPD, rESAT-6:CFP-10, or pokeweed mitogen. Stimulation was similar between formats, demonstrating the potential for use of 96-well plates to minimize reagent use and streamline large scale testing. Likewise, stimulation at 37°C and 33°C were equivalent; however, a culture at 29°C resulted in reduced IFN-gamma production and antigen specific responses were undetectable at 25°C and 22°C. Antigens are usually stored at 2-8°C (tuberculins) or at -80°C (recombinant proteins). Responses with recombinant antigens (i.e., rESAT-6:CFP-10, TB10.4, TB27.4, MPB83) stored at 4°C for 24h and at 20°C for 8h were comparable to that of antigens thawed immediately from -80°C. Together, these findings offer technical opportunities and potential limitations for testing of new antigens under the constraints of field application. These approaches may be particularly relevant for the development of IGRA’s for human TB in developing countries. Free-ranging white-tailed deer are reservoirs of M. bovis infection for cattle in MI, USA. A capture, test, and cull strategy is being evaluated as a method for limiting transmission of TB from deer to cattle. A prompt and accurate animal-side test is required for this strategy to be feasible. To test the feasibility of candidate tests, 760 serum samples were collected from hunter-killed deer and evaluated using a panel of antibody-based tests. Sensitivities ranged from 46 to 68%, while specificities and negative predictive values were all > 92%; thus demonstrating the potential for reasonably accurate results, even under extreme field conditions. Tuberculosis in elephants is an important re-emerging zoonotic disease caused primarily by M. tuberculosis. Diagnosis relies on serology and trunk wash culture. Elephants, as with humans, may receive chemotherapy for the treatment of TB; however, successful cure is difficult and expensive. A test for monitoring on-going treatment success and/or relapse after therapy would be useful. Archived longitudinal serum samples from four infected elephants receiving antibiotic therapy were evaluated for antibody responses to TB antigens via Multi-Antigen Print Immunoassay (MAPIA, Chembio Diagnostics). Results indicate that responses to certain antigens (e.g., Acr1 and Mtb48) wane in response to successful therapy; whereas, responses to other antigens (e.g., ESAT-6) are unaffected. Also, antibody responses increased in intensity and numbers of antigens recognized in animals with relapsing disease. Together, these findings demonstrate the utility of studies with non-human hosts of TB for development of diagnostic strategies to detect TB in humans and potentially to monitor therapy. Further, studies with samples from cattle and other hosts of TB may prove useful for the discovery and validation of new readouts of infection, such as granulysin, IL-21, nitric oxide and other biomarkers.