Background

Bovine tuberculosis (BTB), caused by Mycobacterium bovis, is a corrosive, insid­ious, debilitating, and contagious infectious disease of domesticated and wild ani­mals and of humans.

The World Organization for Animal Health (OIE) lists BTB as a notifiable disease as it considers it to be of socioeconomic or public health importance within countries, with a negative impact on the international trade of animals and animal products and hence local livelihoods (Benkirane 1998; Skuce and Neill 2004). Because of its spread to wildlife and the establishment of wildlife maintenance hosts, BTB has the potential to affect the well-being of wildlife populations and the sustainability of ecosystems (Renwick et al. 2006). Countries with a thriving cattle industry apply regulations that control the trade of animals and their products to protect the national herd from the introduction of BTB, its spread to wildlife, to limit the risk of zoonotic human infection, and to prevent reintroduction of the disease following its eradication (Cousins 2001).

The disease in the various species is characterized by the development of tuberculous granulomas in the lungs, lymph nodes, intestines, liver, kidneys, and other organs, thereby affecting their health that eventually has a detrimental effect on their productivity. Presentation of the disease is variable: clinical signs are absent in the early stages, whereas animals with advanced disease present with non-specific signs such as weakness, anorexia, emaciation, and coughing. The characteristics of the disease and its manifestation are species-dependent and are usually determined by the route by which the animals are infected.

Mycobacterium bovis, the etiological agent of BTB, is a member of the Myco­bacterium tuberculosis complex (MTC) (Skuce et al. 2012). Contrary to M. tuberculosis, it has an exceptionally wide mammalian host range (domesticated animals, wildlife, and humans), and it also has the ability to persist in the environ­ment, the time of its survival being dependent on local climatic and environmental conditions (O’Reilly and Daborn 1995). It is important too as a significant public health threat as the infection causes zoonotic TB in humans following their close contact with infected animals or after consuming M. bovis-containing raw milk and milk products (Cosivi et al. 1998). Based on experience gained to date in countries actively attempting to eradicate the disease, it is clear that BTB is one of the most challenging endemic diseases to deal with, because of its complex epidemiology, the insidious nature of the disease, and the multiple hosts that sustain the infection within ecosystems. It is generally considered to be one of the neglected zoonotic diseases, and it is increasingly attracting the attention of the international community because of its quest to eradicate human tuberculosis in the foreseeable future.

2.2