Submitted to: Veterinary Record
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/2007
Publication Date: 2/16/2008
Citation: Waters, W.R., Palmer, M.V., Thacker, T.C., Orloski, K., Nol, P., Harrington, N.P., Olsen, S.C., Nonnecke, B.J. 2008. Blood Culture and Stimulation Conditions for the Diagnosis of Tuberculosis in Cervids by the Cervigam Assay. Veterinary Record. 162(7):203-208. Interpretive Summary: Captive deer are included in the Uniform Methods and Regulations for the eradication of bovine tuberculosis within the United States. In the past, tuberculosis has been spread from infected captive deer to cattle and bison. The current approved method for detecting tuberculous deer is the skin test. Improved diagnostic methods are urgently needed as skin testing procedures are not widely accepted by the cervid industry. In this study, a blood-based test was evaluated for potential use as an initial tuberculosis screening test. The validity of the test was confirmed for use with samples from reindeer. Inconsistent and poor responses to the positive control stimulant were detected with samples from white-tailed deer, fallow deer, and elk; indicating that this test is not suitable in its current state for use with samples from these species. These findings are useful for the continued development of improved control strategies for bovine tuberculosis, particularly in countries with significant captive deer industries.
Technical Abstract: Mitogen and antigen induced interferon-gamma (IFN-gamma) responses of peripheral blood leukocytes from cervids were evaluated using a commercial, whole blood assay for the cytokine (Cervigam trademark, Prionics AG). Whole blood was from Mycobacterium bovis-infected white-tailed deer and reindeer, M. bovis BCG-vaccinated white-tailed deer and elk, and non-vaccinated/non-infected white-tailed deer, fallow deer, elk, and reindeer. When evaluating samples from M. bovis-infected white-tailed deer, responses to pokeweed mitogen (PWM) varied with time and between individuals. The magnitude of responses to PWM and M. bovis purified protein derivative (PPD) were positively associated, justifying use of PWM induced IFN-gamma secretion as a means for discriminating mycobacterial response capacity. Numerous samples from tuberculosis-free captive herds at varying locales within the US also were evaluated. Four percent of fallow deer, 20% of elk, 44% of white-tailed deer, and 91% of reindeer had responses to PWM exceeding 0.25 delta optical density (i.e., PWM stimulation minus no stimulation), indicating an unacceptable level of detection in each of the species except reindeer. Specificity of responses to mycobacterial antigens (i.e., M. bovis PPD and rESAT-6:CFP10), excluding animals not responding to PWM, ranged from 78% to 100% and was dependent upon cervid species and method of data interpretation (i.e., positive response cut-off value). These findings demonstrate the validity of the Cervigam (trademark) assay for detection of TB in reindeer; however, further development of the assay will be required before using in surveillance programs for white-tailed deer, fallow deer, and elk.