Development and evaluation of an interferon-γ release assay in Asian elephants (Elephas maximus)

Asian elephant (Elephas maximus) is an endangered species according to The IUCN Red List of Threatened Species [2]. There are approximately 208 captive Asian elephants in Nepal which are primarily used for patrolling protected areas, in eco-tourism, and for wildlife research projects [12]. Asian elephants are susceptible to many infectious diseases, and currently infection by intracellular pathogens like M. tuberculosis [8, 11] and elephant endotheliotropic herpesviruses [13] are increasingly seen. A cell-mediated immune response is elicited by the body during the early stages of infection by intracellular pathogens including M. tuberculosis. Interferon-γ (IFN-γ) is one of the major cytokines secreted mainly by Th1 and Natural Killer cells. Mediated by the up regulation of reactive oxygen intermediates and toxic nitric oxide (NO), IFN-γ causes the activation of macrophages that are programmed to kill obligate intracellular microbes [3]. Cell-mediated immunity is activated earlier than humoral immunity. IFN-γ plays an important role in the immuno-pathogenesis of tuberculosis (TB) [5]. Bovigam (Prionics AG, Zurich, Switzerland) was the first commercial IFN-γ release assay (IGRA) developed for the diagnosis of TB in bovine species. Quantiferon Gold-in-Tube (Cellestis Inc., Melbourne, Australia) was later developed as an IGRA for TB diagnosis in humans. Recently, IGRAs have also been developed in some wildlife species including deer species [14], lions [7] and white rhinoceros [9] for the diagnosis of TB. The purpose of this study was to develop and evaluate an Asian elephant-specific IGRA and see its potential as a diagnostic tool for diseases, such as TB in this species.