IP-10: A potential biomarker for detection of Mycobacterium bovis infection in warthogs (Phacochoerus africanus)

Bovine tuberculosis (bTB) is endemic in several areas of South Africa and has been reported in multiple species, including common warthogs (Phacochoerus africanus). Limited diagnostic tests and disease control programs exist for African wildlife. Thus, there is a need to develop techniques for bTB detection in species such as warthogs to assess their role in disease maintenance and spread in multi-host ecosystems. In this study, we obtained blood samples from warthogs in bTB endemic areas to investigate biomarkers for detection of Mycobacterium bovis infection. Warthog whole blood was incubated in QuantiFERON (R) TB Gold In-Tube tubes and pathogen specific release of interferon gamma (IFN-gamma) and interferon gamma induced protein 10 (IP-10) was measured by a sandwich enzyme-linked immunosorbent assay. Although we were unable to measure IFN-gamma, we could successfully measure IP-10. The IP-10 assay was able to distinguish between M. bovis-infected and M. bovis-culture negative warthogs, within bTB endemic areas, with an assay specific sensitivity of 68% and specificity of 84%. Of the 88 M. bovis-exposed warthogs screened, 42% were IP-10 test positive. These results indicate warthogs develop a measurable cell-mediated immune response after antigen stimulation of whole blood, which can distinguish between M. bovis-infected and M. bovis-culture negative animals. Thus, the IP-10 assay shows promise as an ante-mortem test to diagnose bTB in warthogs.