Parallel measurement of IFN-γ and IP-10 in QuantiFERON®-TB Gold (QFT)plasma improves the detection of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

The QuantiFERON®-TB Gold (QFT)stimulation platform for cytokine release is a novel approach for diagnosis of bovine tuberculosis in wildlife species. Plasma interferon gamma (IFN-γ)is routinely measured to detect immune sensitization to Mycobacterium bovis. However, the cytokine interferon gamma-inducible protein 10 (IP-10)has been proposed as an alternative, more sensitive, diagnostic biomarker. In this study, we investigated the use of the QFT system with measurement of IFN-γ and IP-10 in parallel to identify M. bovis-infected African buffaloes. The test results of either biomarker in a cohort of M. bovis-unexposed buffaloes (n = 70)led to calculation of 100% test specificity. Furthermore, in cohorts of M. bovis culture-positive (n = 51)and M. bovis-suspect (n = 22)buffaloes, the IP-10 test results were positive in a greater number of animals than the number based on the IFN-γ test results. Most notably, when the biomarkers were measured in parallel, the tests identified all M. bovis culture-positive buffaloes, a result neither the single comparative intradermal tuberculin test (SCITT)nor Bovigam® IFN-γ release assay (IGRA)achieved, individually or in parallel. These findings demonstrate the diagnostic potential of this blood-based assay to identify M. bovis-infected African buffaloes and a strategy to maximise the detection of infected animals while maintaining diagnostic specificity and simplifying test procedures.