Detection of Mycobacterium tuberculosis complex infection in Asian elephants (Elephas maximus) using an interferon gamma release assay in a captive elephant herd

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.

Tuberculosis seroprevalence and comparison of hematology and biochemistry parameters between seropositive and seronegative captive Asian elephants of Nepal

“…We found that 33 (21.56%) elephants were seropositive using the ElephantTB Stat-Pak® Assay. Similar seropositive rates have been reported in captive elephants in Malaysia 15.87% (10/63) [24], Thailand 30% (18/60) [35], and Laos 36% (29/80) [12].…”

“…Asian elephants are mainly reported to be affected and the majority of cases are due to Mycobacterium tuberculosis, a causative agent of human TB [19,22]. Culture-confirmed cases and TB seroprevalence rates in captive elephants have been reported from several Asian elephant range countries: Nepal [20,[25][26][27], Thailand [2][3]35], India [36], Malaysia [24], and Laos [12]. TB has also been reported in captive elephants from USA [22][23], Australia [37], Sweden [13], and Japan [39], suggesting a worldwide distribution.…”

Shedding of Mycobacterium bovis in respiratory secretions of free‐ranging wild dogs ( Lycaon pictus ): Implications for intraspecies transmission

“…The infection prevalence of M. bovis based on culture of ororespiratory samples (OS and BAL) was 4%, which was significantly lower than the estimated prevalence based on IGRA (79.1%) in this population. This discrepancy could be due to a predominant cellmediated immune response in early infection (without shedding) or in animals that have cleared infection, similar to other species (van der Heijden et al, 2020;O'Halloran et al, 2018;Songthammanuphap et al, 2020). It is also possible that IGRA-positive wild dogs that may be containing or clearing infection are less likely to shed M. bovis.…”

Monitoring IgG against Mycobacterium tuberculosis proteins in an Asian elephant cured of tuberculosis that developed from long-term latency

“…Previous studies have shown that the tuberculin skin test is not sufficiently sensitive in elephants 16 . Interferon-gamma release assay (IGRA), a recent standard test in humans, has not yet been practical in elephants although there have been some attempts to develop it 17 – 19 . A rapid immuno-test kit, Dual Path Platform (DPP) VetTB assay for elephants (Chembio Diagnostic Systems, Medford, NY), is used worldwide for elephant TB screening 20 , 21 .…”