The application of immunological biomarkers and enhanced pathogen detection for the epidemiological characterisation of bovine tuberculosis in African Rhinoceros

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dc.contributor.advisorMiller, Michele Annen_ZA
dc.contributor.advisorGoosen, Wynand Johanen_ZA
dc.contributor.advisorWitte, Carmelen_ZA
dc.contributor.authorDwyer-Leonard, Rebecca Annen_ZA
dc.contributor.otherStellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Molecular Biology and Human Genetics.en_ZA
dc.date.accessioned2024-01-15T08:42:03Zen_ZA
dc.date.accessioned2024-04-26T23:09:00Zen_ZA
dc.date.available2024-01-15T08:42:03Zen_ZA
dc.date.available2024-04-26T23:09:00Zen_ZA
dc.date.issued2024-01en_ZA
dc.descriptionThesis (PhD)--Stellenbosch University, 2024.en_ZA
dc.description.abstractENGLISH ABSTRACT: African rhinoceros, specifically the black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros, are iconic species that are under threat due to poaching for their horns, range/habitat loss, unbalanced genetic/demographic structure, climate change, and infectious diseases, including tuberculosis (TB). Mycobacterium bovis (M. bovis) infection, a cause of TB, has been identified in African rhinoceros populations in Kruger National Park (KNP), South Africa. An interferon-gamma release assay (IGRA) is routinely applied for testing of individuals earmarked for translocation out of the park, and for general surveillance purposes. However, relatively little is understood about the overall susceptibility and pathogenesis of TB in these species, and its impact on affected populations. This study had four broad aims: i.) to collate information on the epidemiology of Mycobacterium tuberculosis complex (MTBC) infections in African rhinoceros, ii.) to determine prevalence and risk factors for M. bovis infection in KNP rhinoceros, iii.) to assess the impact of refrigeration and delayed stimulation of rhinoceros whole blood on mitogen stimulated interferon-gamma (IFN-γ) production, to increase flexibility in implementation of testing, and iv.) to determine whether MTBC can be detected in nasal swabs from rhinoceros with immunological evidence of infection, as an indication of potential infectiousness. Drawing from existing literature on MTBC infections in other species and contexts, a foundational understanding of TB epidemiology in rhinoceros species was developed. In other species, demographic risk factors include sex and age, with males and adults generally being at higher risk than females and younger individuals. Review of limited historical information reflected similar age- and sex-associated patterns for TB in captive African rhinoceros, with more reports of TB disease in black rhinoceros than white rhinoceros. Intra-species transmission of MTBC in rhinoceros was also considered to be a potential source of infection. Free-ranging rhinoceros in bovine TB (bTB) endemic areas may be exposed to MTBC, likely shed by maintenance hosts in KNP such as African buffaloes (Syncerus caffer), greater kudus (Tragelaphus strepsiceros), or warthogs (Phacochoerus africanus), through shared environmental niches, and resources. Based on previous reports, hypotheses were generated then investigated in a population-based study of M. bovis infection in 437 African rhinoceros in KNP. We determined an estimated overall infection prevalence of 15.4% (95% CI: 10.4-21.0%) based on mycobacterial culture and IGRA results for animals sampled between 2016-2020. Notably, a significant spatial clustering of cases was detected near the southwestern park border, although infection was widely distributed. Multivariable logistic regression models, including demographic and spatiotemporal variables, showed a significant, increasing probability of M. bovis infection in white rhinoceros based on increased numbers of African buffalo herds in the vicinity of the rhinoceros sampling location. Spillover of infection from African buffaloes to white rhinoceros sharing the environment was suspected. There was also a significantly higher proportion of M. bovis infection in black rhinoceros in the early years of the study (2016-2018) than in 2019 and 2020, which coincided with periods of intense drought, although other temporal factors could be implicated. Species of rhinoceros, age, and sex were not identified as risk factors for M. bovis infection. Ante-mortem surveillance for M. bovis infection in the Kruger National Park (KNP) rhinoceros population currently relies on results from (QFT)-Mabtech equine interferon-gamma (IFN-γ) release assay (IGRA). However, the requirement for same-day processing of rhinoceros blood samples for the IGRA is a logistical challenge to performing this test, particularly in remote locations. A pilot study showed that relative concentrations of IFN-γ (based on optical density values) in mitogen stimulated whole blood plasma decreased significantly with increased time blood was stored post-collection and prior to QFT stimulation. These findings support a need for same-day processing of rhinoceros blood samples for QFT-IGRA testing, as per the current practice to ensure optimal test performance. It was previously unknown whether M. bovis-infected rhinoceros could shed mycobacteria in respiratory secretions. Previous studies suggested that subclinically M. bovis-infected rhinoceros may pose minimal transmission risk. However, recent advances that have improved detection of MTBC members in paucibacillary samples prompted further investigation of respiratory secretions from rhinoceros with immunological evidence of infection, to elucidate the potential for mycobacterial shedding. A pilot study detected M. bovis in 14/64 (22%; 95% CI: 13-33%) of the IGRA positive rhinoceros, and none in the IGRA negative rhinoceros (n = 11) studied, suggesting that M. bovis-infected rhinoceros may be a source of infection for other susceptible animals sharing the environment. Overall, these studies address important knowledge gaps related to surveillance and epidemiology of TB in African rhinoceros, specifically, the free-ranging populations in KNP. This has created awareness of the potential threat of this pathogen to the conservation of these species and highlighted important areas for future research that will contribute to understanding the multi-host TB ecosystem in KNP and other complex systems.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Afrikaanse renosters, spesifiek die swart (Diceros bicornis) en wit (Ceratotherium simum) renosters, is ikoniese spesie wat bedreig word deur stropery vir hul horings, verlies van habitat, ongebalanseerde genetiese en demografiese struktuur, klimaatverandering, en aansteeklike siektes, insluitend tuberkulose (TB). Mycobacterium bovis (M. bovis) infeksie, 'n oorsaak van TB, is geïdentifiseer in Afrika-renosters in die Kruger Nasionale Park (KNP), Suid-Afrika. 'n Interferon-gamma vrystellingstoets (IGRA) word gereeld gebruik vir toetsing van individue wat vir verplasing uit die park gemerk is, en vir algemene toesig. Tog is daar relatief min begrip van die algemene vatbaarheid en ontwikkeling van TB in hierdie spesies, en die impak daarvan op die geaffekteerde bevolkings. Hierdie studie het vier breë doelwitte gehad: i) om inligting oor die epidemiologie van Mycobacterium tuberculosis kompleks (MTBC) infeksies in Afrika-renosters bymekaar te bring, ii) om die voorkoms en risikofaktore vir M. bovis infeksie in KNP-renosters te bepaal, iii) om die impak van verkoeling en vertraagde stimulasie van renosters se volbloed op mitogeen gestimuleerde IFN-γ produksie te beoordeel, vir meer vryheid in toetse, en iv) om vas te stel of MTBC in neus deppers van renosters met immunologiese bewyse van infeksie opgespoor kan word, as bewys van potensiële aansteeklikheid. Met behulp van bestaande literatuur oor MTBC-infeksies in ander spesies en kontekste, is ‘n grondliggende begrip van TB-epidemiologie in renosterspesies ontwikkel. In ander spesies is die volgende demografiese risikofaktore van belang. Geslag en ouderdom, waar manlike en volwassenes algemeen 'n hoër risiko dra as vroulike en jonger individue. Beperkte historiese inligting het soortgelyke ouderdoms- en geslagsverwante patrone vir TB in gekoërdineerde Afrika-renosters weerspieël, met meer verslae van TB-siekte in swart renosters wanneer dit versgelyk word met wit renosters. Intra-spesie oordrag van MTBC in vrylopende renosters kon as 'n moontlikheid beskou word. Gebaseer op vorige verslae was hipotese geskep en word verder geondersoek in 'n bevolkingsgebaseerde studie van M. bovis in 437 Afrika-renosters in KNP. Ons het 'n geskatte algehele infeksie voorkoms van 15.4% (95% CI: 10.4-21.0%) gerapporteer en hierdie data was gebaseer op mikrobakteriële kultuur- en IGRA-resultate tussen 2016-2020. 'n Beduidende ruimtelike groepering van gevalle is naby die suidwestelike parkgrens opgespoor, alhoewel infeksie wye verspreiding getoon het. Meerveranderlike logistiese regressiemodelle, insluitend demografiese en tydruimtelike veranderlikes, het 'n beduidende, toenemende waarskynlikheid van M. bovis infeksie in wit renosters getoon. Hierdie was gebaseer op ‘n verhoogde aantal Afrikaanse buffeltroppe in die nabyheid van die renosters se monsterneming pleak. Daar is vermoed dat besmetting van Afrikaanse-buffels na witrenosters wat die omgewing deel, oorgeloop het. Aangesien Afrikaanse buffels belangrike onderhoudshospers vir M. bovis in KNP is, word besmettingsoorskryding van hierdie gasheer-spesie na wit renosters wat die omgewing deel, vermoed. Daar was ook 'n beduidende hoër proporsie M. bovis infeksie in swart renosters in die vroeë jare van die studie (2016-2018) in vergelyking met 2019 en 2020, wat saamgeval het met periodes van intens droogte, alhoewel ander temporele faktore geïmpliseer kan word. Spesies van renoster, ouderdom, en geslag was nie as risikofaktore vir M. bovis infeksie geïdentifiseer nie. Voor-doodse ondersoek vir M. bovis infeksie in die KNP se renosterbevolking steun tans op resultate van die QuantiFERON-TB Gold (In-Tube) Plus (QFT)-Mabtech perde interferongamma (IFN-γ) vrystellingstoets (IGRA). Maar die vereiste vir dieselfde-dag verwerking van renoster bloedmonsters vir die IGRA bly steeds 'n logistieke uitdaging om hierdie toets uit te voer, veral in afgeleë gebiede. 'n Loodsstudie het getoon dat relatiewe konsentrasies van IFNγ (gebaseer op optiese digtheidswaardes) in mitogeen gestimuleerde volbloedplasma beduidend afgeneem het met toenemende tyd wat bloed na versameling; en voor QFT stimulasie gestoor is. Hierdie bevindinge ondersteun 'n behoefte aan dieselfde-dag prosessering van renoster bloedmonsters vir QFT-IGRA toetsing om voort te gaan soos die huidige praktyk, vir optimale toets prestasie. Dit was voorheen onbekend of M. bovis-besmette renosters mikro-organismes in respiratoriese afskeidings kon afskei. Vorige studies het voorgestel dat subklinies M. bovis-besmette renosters kan minimale oordragrisiko inhou.. Onlangse vooruitgang wat die opsporing van MTBC lede in paucibacillêre monsters verbeter het, het gelei na verdere ondersoek van respiratoriese afskeidings van renosters met immunologiese bewyse van infeksie. Hierdie study is om die potensiaal vir mikrobakteriese afskeiding toe te lig. 'n Loodsstudie het M. bovis in 14/64 (22%; 95% CI: 13-33%) van die IGRA-positiewe renosters gevind, en geen in die IGRAnegatiewe renosters (n = 11) wat ondersoek is nie, wat aandui dat M. bovis-besmette renosters 'n bron van infeksie vir ander vatbare diere wat die omgewing deel, mag wees.af_ZA
dc.description.versionDoctoralen_ZA
dc.format.extentxviii, 205 pagesen_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130590en_ZA
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshTuberculosis in animals en_ZA
dc.subject.lcshBiochemical markersen_ZA
dc.subject.lcshEndangered speciesen_ZA
dc.subject.lcshMycobacterium bovisen_ZA
dc.titleThe application of immunological biomarkers and enhanced pathogen detection for the epidemiological characterisation of bovine tuberculosis in African Rhinocerosen_ZA
dc.typeThesisen_ZA
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