Abstract
Mycobacterium bovis is the cause of tuberculosis (TB) in a wide range of species, including white rhinoceroses (Ceratotherium simum). Control of the disease relies on the indirect detection of infection by measuring pathogen-specific responses of the host. These are poorly described in the white rhinoceros and this study aimed to characterize the kinetics of immune responses to M. bovis infection in this species. Three white rhinoceroses were infected with M. bovis and their immune sensitization to this pathogen was measured monthly for 20 months. Cell-mediated immunity was characterized in whole blood samples as the differential release of interferon-gamma in response to bovine purified protein derivative (PPDb) and avian PPD (PPDa) as well as the release of this cytokine in response to the M. bovis proteins 6 kDa early secretory antigenic target (ESAT-6)/10 kDa culture filtrate protein (CFP-10). Humoral immunity was quantified as the occurrence or the magnitude of antibody responses to the proteins ESAT-6/CFP-10, MPB83, MPB83/MPB70, and PPDb. The magnitude and duration of immune reactivity varied between individuals; however, peak responses to these antigens were detected in all animals circa 5–9 months postinfection. Hereafter, they gradually declined to low or undetectable levels. This pattern was associated with limited TB-like pathology at postmortem examination and appeared to reflect the control of M. bovis infection following the development of the adaptive immune response. Measurement of these markers could prove useful for assessing the disease status or treatment of naturally infected animals. Moreover, immune responses identified in this study might be used to detect infection; however, further studies are required to confirm their diagnostic utility.
Highlights
White rhinoceroses (Ceratotherium simum) are classified as “Near Threatened” by the International Union for Conservation of Nature, with the majority of animals occurring in South Africa [1]
While the specific patterns of immune reactivity varied between individuals, peak responses were detected in all three animals circa 5–9 months PI, after which they gradually declined to low or undetectable levels
The onset of adaptive immunity toward M. tuberculosis requires the active replication of the pathogen in lymph nodes draining the site of infection [13]
Summary
White rhinoceroses (Ceratotherium simum) are classified as “Near Threatened” by the International Union for Conservation of Nature, with the majority of animals occurring in South Africa [1]. A substantial number occur in the greater Kruger National Park (KNP) and the Hluhluwe-iMfolozi Park (HiP). Because of their economic value and threatened conservation status, animals from these populations are regularly translocated to other reserves and privately owned collections. Movement of animals from these areas could present a risk of translocating Mycobacterium bovis, a major cause of tuberculosis (TB). This pathogen can infect a wide variety of domestic and wildlife hosts, including rhinoceros species [2] and has become established in both the KNP and HiP [3]. The recent detection, in the KNP, of a case of severe pulmonary TB in a black rhinoceros [4] and confirmed M. bovis granulomas in lymph nodes of four white rhinoceroses (unpublished data) highlights the potential risk of movement of these species
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