ARS | Publication request: Update on Comparative Studies for Diagnosis of Bovine Tuberculosis Using The Interferon Gamma (IFN-gamma) Assay with Tuberculins or Alternative Antigens for Whole Blood Stimulation

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 7, 2009
Publication Date: October 7, 2009
Citation: Schroder, B., Hardegger, R., Moyen, J.L., Gormley, E., Waters, W.R., Palmer, M.V., Thacker, T.C., Nonnecke, B.J., Keck, N., Egnuni, T., Whelan, A., Vordermeier, H.M., Raeber, A.J. 2009. Update on Comparative Studies for Diagnosis of Bovine Tuberculosis Using The Interferon Gamma (IFN-gamma) Assay with Tuberculins or Alternative Antigens for Whole Blood Stimulation [abstract].

Technical Abstract: Bovine Tuberculosis is a respiratory disease caused by Mycobacterium bovis (M. bovis). It is a major infectious disease found worldwide in domestic animals, particularly cattle, as well as in certain wildlife populations. Although the disease has been effectively eliminated in many countries and regions, it is increasingly reappearing as a result of host reservoirs in wild animal populations, importation of infected animals, or as resurgence from former infected herds. The success of bovine tuberculosis eradication programs in many countries have relied on ante mortem diagnostic tests measuring cell-mediated immune (CMI) responses such as the tuberculin skin test or the interferon gamma test. The BOVIGAM® interferon gamma (IFN-gamma) assay constitutes a laboratory-based tuberculosis test and is widely used complementary to the tuberculin skin test. The assay consists of a first step culturing whole blood with antigens and stimulating leucocytes to produce IFN-gamma which is quantified by ELISA in a second step. Diagnosis is based on a comparative measurement with avian and bovine tuberculins. Numerous field trials showed that the IFN-gamma assay was more sensitive than the intradermal skin test for diagnosis of tuberculosis. However, specificity of the IFN-gamma assay was found to be slightly lower than the skin test suggesting limited use of the IFN-gamma assay as a stand-alone screening tool in cattle herds that are either free or have a low prevalence of tuberculosis. In order to increase the specificity of the IFN-gamma test, defined antigens such as ESAT-6 or CFP-10 in combination with other highly specific antigens encoded by the genome of M. bovis have been evaluated in field trials. Here we show, that a combination of antigens including ESAT-6 and CFP-10 showed a specificity of 99.5 % - 100 % in cattle from TB-free regions whereas sensitivities assessed in herds with skin test reactors in France and Ireland showed comparable sensitivities as with tuberculins. These results suggest that IFN-gamma testing comprising stimulation with well characterized antigen cocktails can be used as a stand-alone test system for tuberculosis in cattle.