Epidemiology of Tuberculosis in Multi-Host Wildlife Systems: Implications for Black (Diceros bicornis) and White (Ceratotherium simum) Rhinoceros

Abstract

Cases of tuberculosis (TB) resulting from infection with Mycobacterium tuberculosis complex (MTBC) have been recorded in captive white ( Ceratotherium simum ) and black ( Diceros bicornis ) rhinoceros. More recently, cases have been documented in free-ranging populations of both species in bovine tuberculosis (bTB) endemic areas of South Africa. There is limited information on risk factors and transmission patterns for MTBC infections in African rhinoceros, however, extrapolation from literature on MTBC infections in other species and multi-host systems provides a foundation for understanding TB epidemiology in rhinoceros species. Current diagnostic tests include blood-based immunoassays but distinguishing between subclinical and active infections remains challenging due to the lack of diagnostic techniques. In other species, demographic risk factors for MTBC infection include sex and age, where males and adults are generally at higher risk than females and younger individuals. Limited available historical information reflects similar age- and sex-associated patterns for TB in captive black and white rhinoceros, with more reports of MTBC-associated disease in black rhinoceros than in white rhinoceros. The degree of MTBC exposure in susceptible wildlife depends on their level of interaction, either directly with other infected individuals or indirectly through MTBC contaminated environments, which is dependent on the presence and abundance of infected reservoir hosts and the amount of MTBC shed in their excreta. Captive African rhinoceros have shown evidence of MTBC shedding, and although infection levels are low in free-ranging rhinoceros, there is a risk for intraspecies transmission. Free-ranging rhinoceros in bTB endemic areas may be exposed to MTBC from other infected host species, such as the African buffalo ( Syncerus caffer ) and greater kudu ( Tragelaphus strepsiceros ), through shared environmental niches, and resource co-utilization. This review describes current knowledge and information gaps regarding the epidemiology of TB in African rhinoceros.

Histopathological Investigations and Molecular Confirmation Reveal Mycobacterium bovis in One-Horned Rhinoceros (Rhinoceros unicorns)

“…The changes and distribution of lesions caused by M. bovis mainly depend upon the possible route of infection. Very few information is available about the gross and microscopic lesions due to M. bovis in captive individuals' rhinoceroses [ 27 , 28 ] and very rare in free-ranging wild animals. Similar pulmonary lesions have been seen in a semicaptive black rhinoceros due to natural infection with M. bovis [ 29 ].…”

Epidemiology ofMycobacterium bovisinfection in free-ranging rhinoceros in Kruger National Park, South Africa

“…African rhinoceros ( Diceros bicornis , Ceratotherium simum ) are currently under threat due to poaching activity and habitat destruction, as well as the underrecognized threat of infectious diseases ( 1 , 2 ). Mycobacterium bovis infection has been confirmed in the African rhinoceros population in Kruger National Park (KNP), South Africa ( 3 – 6 ).…”

“…Mycobacterium bovis infection has been confirmed in the African rhinoceros population in Kruger National Park (KNP), South Africa ( 3 – 6 ). The discovery of M. bovis infection in this population has led to a quarantine of rhinoceros intended for translocation from the park to other protected areas, which has significant conservation consequences ( 1 ). The paucity of knowledge regarding the epidemiology and risk of transmission from infected rhinoceros has become evident when assessing impact on the KNP population and potential for spread to other populations ( 1 ).…”

“…Black and white rhinoceros in KNP share environmental resources (including browse/grazing, and water sources) with potentially M. bovis –infected African buffaloes ( 8 – 10 ), greater kudu ( Tragelaphus strepsiceros ) ( 13 , 14 ), warthogs ( Phacochoerus africanus ) ( 15 ), and other species ( 12 ). A recent review of potential scenarios for interspecies transmission has suggested that rhinoceros may become infected with M. bovis in ecosystems containing other infected hosts ( 1 ). Interspecies spread has been demonstrated in other systems, including badgers and cattle in the United Kingdom ( 16 ), wild boars, deer, and cattle in Spain ( 17 ), and deer and cattle in the United States ( 18 ).…”

“…Mechanisms of transmission between herbivores are poorly understood but have been attributed to indirect interaction through shared resources such as pastures, feed, or water holes that are contaminated by M. bovis –shedding hosts ( 17 , 19 , 20 ). The potential for intraspecies transmission between rhinoceros is also plausible based on antemortem detection of mycobacteria in respiratory secretions ( 1 , 21 ).…”