ARS | Publication request: Comparison of Tuberculin Activity in the Interferon-gamma Assay for the Diagnosis of Bovine Tuberculosis

Submitted to: Veterinary Record
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 9, 2009
Publication Date: August 28, 2010
Citation: Schiller, I., Vordermeier, H.M., Waters, W.R., Kyburz, A., Cagiola, M., Whelan, A., Palmer, M.V., Thacker, T.C., Meijlis, J., Carter, C., Egnuni, T., Hardegger, R., Marg-Hauffe, B., Raeber, A., Oesch, B. 2010. Comparison of Tuberculin Activity in the Interferon-gamma Assay for the Diagnosis of Bovine Tuberculosis. Veterinary Record. 167(9):322-326.

Interpretive Summary: Bovine tuberculosis (bTB), caused by Mycobacterium bovis, accounts for up to 10% of human TB cases in developing countries and is increasing in cattle in the US and UK. Control of bTB is hindered by the presence of numerous wildlife reservoirs such as white-tailed deer, European badgers, and brush-tailed possums. Reasons for the failure to eradicate the disease are multi-factorial. Limitations in the sensitivity and specificity of diagnostic tests are factors contributing to the persistence of bTB. Test interpretation and accuracy are confounded by variations in the frequency of tuberculin testing, ambiguities in test result interpretation, and the use of varying tuberculin preparations The Bovigam™ assay is approved for use within the United States as a complimentary test for bovine tuberculosis. This assay relies on a specific response to the tuberculosis agent. In the present study, reagents used in the test and test applications were evaluated to improve test specificity and sensitivity. Knowledge obtained from this study may lead to an improved test for tuberculosis, thereby, advancing the national tuberculosis eradication program.

Technical Abstract: Cattle infected with bovine tuberculosis still represent a serious regulatory and health concern in a variety of countries. Early diagnosis using the in vitro interferon gamma (IFN-g) assay has been applied for more than a decade. Briefly, IFN-g responses in whole blood cultures stimulated with purified protein derivatives (PPDs) from Mycobacterium bovis (PPD-B) or M. avium (PPD-A) are quantitated. The production of a higher amount of IFN-g in cultures stimulated with PPD-B in comparison to PPD-A is indicative of an M. bovis infection. In the present study, different sources and concentrations of PPDs were compared with regard to diagnostic reliability in experimentally- and naturally-infected animals. Significant differences (P < 0.05) between sources and concentrations of PPD for stimulation were detected, indicating the need for standardization of PPDs used in the IFN-g assay. Additionally, we propose a tool named Relative Potency 30 (RP30) that allows rapid comparison of batches and sources of PPDs.