DETERMINATION OF THRESHOLD STIMULATION INDEX FOR IGRAS USING ESAT-6 AND CFP-10 ANTIGENS FOR BOVINE TB DIAGNOSTICS IN INDIA

Abstract

Bovine tuberculosis (bTB) leads to morbidity, mortality and economic losses worldwide and can be controlled by detection and removal of infected animals. Bovigam™, based on IFN-γ release assays, (IGRAs) has been recently approved as an ancillary diagnostic test to the conventional tuberculin skin test (TST). The assay, which is costly kit is based on the use of purified protein derivative (PPD) as antigen, and thus leads to low specificity.  In the present study, the IFN-γ response to bTB was evaluated in vitro with bTB specific antigens ESAT-6 and CFP-10 and the secreted IFN-γ was estimated using in-house standardized bIFN-γ IC-ELISA. The TST negative cattle (n=100) from a bTB low incidence farm were screened to determine the assay stimulation index cut-off for IGRAs. The achieved cut-off was applied in the three reference positive and three reference negative samples for estimation of assay sensitivity and specificity.