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Cattle and domesticated or farmed buffalo
Mycobacterium bovis is the primary source of BTB in cattle, swamp or Asiatic water buffalo (Cousins, 2001). M. bovis causes BTB in cattle and was previously reported to be present in almost every country of the world (Smith et al. 2006). All species of cattle are affected, however, some cattle breeds are more resistant to M. bovis infections (Bos indicus, i.e. Zebu and Brahman) than others (Bos taurus, i.e. European cattle breeds) (O‟Reilly and Daborn, 1995). In Western Azerbaijan, Iran, M. bovis was isolated in one farmed buffalo specimen out of 140 specimens. In this region, buffaloes are bred in close contact with cattle, however, before this report; no incidences of BTB in buffaloes were reported in 26 years (Tadayon et al. 2006). In a study done in Pakistan, Khan and co-workers have noted that domesticated buffaloes which are high milk producers tend to suffer more from bovine tuberculosis (Khan et al. 2008). M. bovis infection in cattle rarely presents clinical disease. More commonly it appears in healthy animals responding to immunological tests based on tuberculin (Collins, 2006). In cattle, as well as in many other animal hosts, the route of transmission can be deduced by the pattern of lesions observed in slaughtered animals. Animal with lesions restricted to the thoracic cavity are presumed to have been infected by the inhalation of aerosols, while those with lesions in the mesenteric lymph nodes are thought to have acquired the infection by ingestion (Pollock and Neill, 2002). However, tuberculosis lesions in cattle are most often found in the lungs and associated lymph nodes, and liver (Neill et al. 1994). In some cases, lesions are most commonly observed in the lower respiratory tract. The upper respiratory tract and associated tissues also displayed the disease in a significant number of cases (De la Rua Domenech et al. 2006).
Respiratory excretion and inhalation of M. bovis is considered to be the main route through which cattle-to-cattle transmission occurs in bovine (Biet et al. 2005).
Transmission and routes of infection in domestic animals
Among domesticated animals, cattle, farmed buffalo and goats are considered reservoir hosts of M. bovis or M. caprae, whereas pigs, cats, dogs, horses and sheep are spillover hosts (Biet et al. 2005; Rodrίgues et al. 2011; Napp et al. 2013). In reservoir hosts, infection can persist through horizontal transfer in the absence of any other source of M. bovis and may as well be transmitted to other susceptible species. In contrast, spillover hosts become infected with M. bovis but the infection only occurs sporadically or persists within these populations if a true maintenance host is present in the ecosysteM. However, if the source is removed, the prevalence for this disease is reduced and it can only be maintained in the long term by re-infection from other sources (Haydon et al. 2002).
Routes of transmission of M. bovis are likely dependent upon the biology of the host animal as well as the environmental variables for areas occupied by the host (Walter et al. 2012). In cattle and other animal hosts, the route of transmission of M. bovis can be deduced from the pattern of lesions observed during post mortem. Animals with lesions restricted to the thoracic cavity are presumed to have been infected by inhalation of aerosols, while those with lesions in mesenteric lymph nodes are thought to have acquired the infection by ingestion (Pollock and Neill, 2002). Inhalation of M. bovis is considered the most probable route of infection due to majority of lesions found in the upper and lower respiratory tract and associated lymph nodes in field cases of cattle (Neill et al. 1994). The development of tuberculosis lesions which invade the airways was thought to be required to facilitate active excretion and aerosol spread of M. bovis in a study conducted in cattle from Northern Ireland (Menzies and Neill, 2000).
Bovine tuberculosis in wildlife species
Cases of M. bovis have been reported in more than 40 free ranging wildlife species (Michel et al. 2010). The importance of BTB in wild animals has been acknowledged. Once infected, many wild animals have shown the potential to act as reservoirs of infection for both domestic cattle and other valuable wildlife species (De Lisle et al. 2002). Two categories of wildlife hosts have been distinguished, that is, the maintenance host and the spill-over host. The localization of lesions in infected animals may play a role in their characterization. Lesions that are mainly found in the thoracic cavity suggest an aerogenic infection, which is commonly observed in maintenance host like cattle (De Lisle et al. 2002). Digestive lesions suggest oral contamination by eating contaminated carcases, which is a characteristic of spill-over species, mostly the carnivores and omnivores.
Wildlife reservoirs are considered to constitute a major impediment to TB control or eradication programmes in some countries (Corner, 2006). These include the Eurasian badger (Meles meles) in the UK and Ireland (Delahay et al. 2002; Griffin et al. 2005). The white-tailed deer (Odocoileus virginianus) is a reservoir of M. bovis in Michigan, USA (Schmitt et al. 1997) and served as a presumptive source of infection for cattle herds, and wild boar (Sus scrofa) and red deer (Cervus elaphus) in Spain (Vicente et al. 2007). The brush-tailed possums (Trichosurus vulpecula) are the primary wild maintenance host of bovine TB in NZ (Morris and Pfeiffer, 1995; Coleman and Caley, 2000; Barron et al. 2013) and are primarily responsible for the transmission of TB in livestock (Coleman and Caley, 2000).
In South Africa (SA), African buffaloes (Syncerus caffer) have been recognised for some time as important role players in the maintenance and transmission of a variety of economically important livestock disease like BTB at the wildlife and/or livestock interface (Michel et al. 2012). Bovine tuberculosis is endemic in African buffalo in the Kruger National Park (KNP) and Hluhluwe-iMfolozi Park (HiP). The infection had spilled-over to several other wildlife species including lion (Panthera leo), kudu (Tragelaphus strepsiceros), chacma baboon (Papio ursinus), leopard (Panthera pardus), cheetah (Acinonyx jubatus), hyena (Crocuta crocuta), honey badger (Mellivora capensis), spotted genet (Genetta tigrina), bushbuck (Tragelaphus scriptus) warthog (Phacochoerus africanus), bush pig (Potamochoerus larvatus) and impala (Aepyceros melampus) (Keet et al. 2000; Bengis et al. 2002; Michel et al. 2006; Michel et al. 2009). The transmission of M. bovis between buffalo herd members occurs most frequently by aerosol (Bengis et al. 1996). Predators and scavengers contract the disease mostly by ingestion of tuberculous tissues (Michel et al. 2006). In kudus, the first clinical sign of tuberculosis is the development of abscesses in the parotid lymph nodes. The abscesses increase with time and eventually rupture to intermittently discharge exudate. The M. bovis containing exudate discharges over long periods from the fistulous nodes below the ears and may contaminate the environment. This is suggested to be the mode of transmission between kudu as well as between kudu and cattle (Bengis et al. 2001). The Kafue lechwe (Kobus leche) antelope in Zambia has been described as a reservoir and source of BTB, and the high prevalence of the disease in the Kafue basin is reported to be a result of the contact that exist between cattle and wildlife species, particularly the lechwe antelopes (Munyeme et al. 2009). In Tanzania, scientists reported the occurrence of M. bovis in wildebeest (Connochaetes taurinus), topi (Damaliscus lunatus) and lesser kudu (Tragelaphus imberbis) sampled from protective areas in Northern Tanzania (Cleaveland et al. 2005).
Chapter 1 General introduction
1.1 Literature Review
1.2 Problem statement
1.3 Aims of the study
1.4 Objectives
References
Chapter 2 Molecular characterization of Mycobacterium bovis isolated from African buffaloes (Syncerus caffer) in Hluhluwe-iMfolozi Park in KwaZulu-Natal, South Africa
2.1 Abstract
2.2 Introduction
2.3 Materials and methods
2.4 Results
2.5 Discussion
2.6 Conclusion
References
Chapter 3 Evaluation of the discriminatory power of variable number of tandem repeat (VNTR) typing of Mycobacterium bovis isolates from southern Africa
3.1 Abstract
3.2 Introduction
3.3 Materials and methods
3.4 Results
3.5 Discussion
3.6 Conclusion
References
Chapter 3.1 Interlaboratory testing beyond diagnosis: Standardisation of a research tool in tuberculosis epidemiology
References
Chapter 4 Evidence of increasing intra and inter-species transmission of Mycobacterium bovis in South Africa: Are we losing the battle
4.1 Abstract
4.2 Introduction
4.3 Materials and methods
4.4 Results
4.5 Discussion
4.6 Conclusion
References
Chapter 5 Wildlife sales: a new man-made wildlife/wildlife interface in South Africa
5.1 Abstract
5.2 Introduction
5.3 Materials and methods
5.4 Results
5.5 Discussion
5.6 Conclusion
References
Chapter 6 CASE REPORT: Isolation and molecular characterization of Mycobacterium bovis causing pulmonary tuberculosis in a horse from South Africa
6.1 Abstract
6.2 Introduction
6.3 Materials and methods
6.4 Results
6.5 Discussion
6.6 Conclusion
References
Chapter 7 Identification and evaluation of tandem repeat sequences derived from whole genome sequences of Mycobacterium bovis isolates from South Africa
7.1 Abstract
7.2 Introduction
7.3 Materials and methods
7.4 Results
7.5 Discussion
7.6 Conclusion
References
Chapter 8 General discussion and conclusion
Appendix
