Abstract
Tuberculosis is highly contagious disease that can be transmitted between humans and animals. Asian elephants (Elephas maximus) in captivity live in close contact with humans in many Asian countries. In this study, we developed an interferon gamma release assay (IGRA) for elephant TB detection using antigens from the MTB complex (MTBC) and nontuberculous mycobacteria (NTM) as stimulating antigens (PPD, ESAT6, CFP10) to elicit a cell-mediated immune response (CMIR). The developed assay was applied to an elephant herd of more than 60 animals in Thailand, and the results were compared with those obtained through serological detection. IGRA has sufficient sensitivity for detecting elephant interferon gamma (eIFNγ) from specific antigen-stimulated PBMCs. Among 60 animals tested, 20 samples (33.3%) showed negative results for both MTBC and NTM infection. Eighteen samples (30%) showed positive responses against PPD from M. bovis and/or ESAT6 and CFP10, indicating MTBC infection. In contrast, only 15.6% showed seropositivity in a commercial serological test kit for elephant TB. The discrepancies between serological and CMIR highlight that the two methods may detect different stages of elephant TB. Therefore, employing both tests may enable them to complement each other in correctly identifying elephants that have been exposed to MTBC.
Highlights
Tuberculosis is highly contagious disease that can be transmitted between humans and animals
According to the report by Une and Mori in 2007, Asian elephants (Elephas maximus) are much more susceptible to M. tb infection than are African elephants (Loxodonta africana); they are at high risk of becoming infected and may spread it to h umans[6]
The limit of detection (LOD) of this ELISA is estimated at 0.241 ng/mL
Summary
Tuberculosis is highly contagious disease that can be transmitted between humans and animals. We developed an interferon gamma release assay (IGRA) for elephant TB detection using antigens from the MTB complex (MTBC) and nontuberculous mycobacteria (NTM) as stimulating antigens (PPD, ESAT6, CFP10) to elicit a cell-mediated immune response (CMIR). IGRA has sufficient sensitivity for detecting elephant interferon gamma (eIFNγ) from specific antigen-stimulated PBMCs. Among 60 animals tested, 20 samples (33.3%) showed negative results for both MTBC and NTM infection. The discrepancies between serological and CMIR highlight that the two methods may detect different stages of elephant TB. Employing both tests may enable them to complement each other in correctly identifying elephants that have been exposed to MTBC. Diagnostic assays detecting humoral immune response (HIR) as antibodies specific for MTB complex antigens in serum have limitations in yielding false positive results from cross-reactivity with environmental mycobacteria[10]
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