Threat of tuberculosis in under-recognized species – TB in African rhinoceros
by Prof. Michele Miller, NRF South African Research Chair in Animal TB
Animal TB Research Group – Dr. Leanie Kleynhans, Dr. Wynand Goosen, Dr. Tanya Kerr, Netanya Bernitz, Josephine Chileshe, Christina Meiring, Candice de Waal, Katrin Smith, Samantha Goldswain, Pamela Ncube
in WDA-AME Newsletter 2021, Vol.5, issue 1
Tuberculosis, caused by one of the members of the Mycobacterium tuberculosis complex (MTBC), is the world’s most deadly infectious disease, according to the World Health Organization. Although extensive resources and research have been committed to this disease in humans, the same is not true for animal tuberculosis, particularly in wildlife. This is especially true in developing countries where national control programs may not exist or be effectively implemented. In addition, many of these same countries also hold important wildlife populations that are threatened by habitat loss, poaching, and potentially disease. Due to the difficulty of detecting and monitoring diseases in wildlife populations, often the risk and threat of disease are under-recognized.
Tuberculosis in rhinoceros has been reported in captive animals going back almost 200 years (Miller et al., 2015). However, due to the lack of clinical signs until disease is advanced and limited diagnostic techniques, cases are often missed until detection after death. Both M. bovis and M. tuberculosis can infect African rhinoceros species. Although an incidental case of M. bovis infection in a captive black rhinoceros that had been wild caught was reported in South Africa (Espie et al., 2009), the first documented case of fatal bovine tuberculosis was discovered in a black rhinoceros in Kruger National Park (KNP) in 2016 (Miller et al., 2017). Since that time, additional cases of incidental M. bovis infection have been found in white rhinoceros in KNP (Miller et al., 2018).
The presence of tuberculosis in a population results in quarantine, restricting animal movement, including conservation programs. With the increasing need to move rhinoceros to safe locations due to poaching as well as reintroductions, quarantine is a significant complication for these populations. As with other species, understanding the risk of transmission and availability of accurate diagnostic tests are crucial to developing an effective management plan and screen animals for translocation. The Animal TB Research Group at Stellenbosch University has been conducting research on multiple aspects of TB in rhinoceros. In vitro interferon gamma production assays have been studied to detect rhinoceros immune responses to detect infection (Parsons et al., Chileshe et al., 2019).
These blood-based tests provide a feasible method for screening rhinoceros for TB. In addition, other biomarkers are currently being investigated to improve detection. In order to determine risk of transmission, studies are also underway to improve detection of mycobacteria in secretions that can be collected by nasal or oral swabs, tracheobronchial lavage, or faeces. In pilot studies, rapid accurate detection of even low levels of M. bovis bacilli can be detected in secretions using a widely available human TB PCR method, GeneXpert MTB/RIF
Ultra (Cepheid). Substantial knowledge gaps remain with regards to TB in African rhinoceros. However, research to improve understanding transmission, susceptibility and pathogenesis in different rhinoceros species, and diagnostic techniques will facilitate our assessment of the impact of TB on rhinoceros and conservation programs.
Chileshe J, Goosen WJ, Buss PE, van Helden PD, Warren R, Parsons SDC, and Miller MA. 2019. A commercial ELISA for detection of interferon-gamma in white rhinoceros. J Vet. Diagn. Invest.
Espie IW, Hlokwe TM, van Pittius NCG, Lane E, Tordiffe AS, Michel AL, Müller A, Kotze A, and van Helden PD. 2009. Pulmonary infection due to Mycobacterium bovis in a black rhinoceros (Diceros bicornis minor) in South Africa. J. Wildl. Dis. 45(4):1187-1193.
Miller MA, Buss P, Parsons SDC, Roos E, Chileshe J, Goosen WJ, van Schalkwyk L, de Klerk-Lorist L-M, Hofmeyr M, Hausler G, Rossouw L, Manamela T, Mitchell EP, Warren R, and van Helden P. 2018. Conservation of white rhinoceros threatened by bovine tuberculosis, South Africa, 2016-2017. Emerg. Inf. Dis. 24(12):2373- 2375.
Miller MA, Buss PE, van Helden PD, and Parsons SDC. 2017. Mycobacterium bovis in a free-ranging black rhinoceros, Kruger National Park, South Africa, 2016. Emerg. Inf. Dis. 23(3):557-558.
Miller M, Michel A, van Helden P, and Buss P. 2016. Tuberculosis in rhinoceros: an underrecognized threat?
Transb. Emerg. Dis.
Parsons SDC, Morar-Leather D, Buss P, Hofmeyr J, McFadyen R, Rutten VPMG, van Helden PD, Miller MA, and Michel AL. 2017. The kinetics of the humoral and interferon-gamma immune responses to experimental Mycobacterium bovis infection in the white rhinoceros (Ceratotherium simum). Front. Immun. 8:1831. 1