5.1 Host range

Mycobacteria have one of the widest host range and affects mammal, birds, fish, reptiles, and amphibians. Cattle and related ruminants such as buffalo and bison are regarded as the main hosts of M. bovis subspecies. Other mammalian hosts include sheep, goats, camels, horses, llamas, pigs, dogs, cats, humans, and nonhuman primates [40]. Many wild animals, including elephants, rhinoceroses, coyotes, mink, otters, seals, sea lions, hares, bears, warthogs, large cats ferrets, and rodents are affected. Known maintenance hosts include possums and ferrets in New Zealand; badgers, raccoons, and foxes in Europe; bison and elk in Canada; and kudu and African buffalo in Africa and white-tailed deer in the USA [9].

hosts include sheep and goats. The low prevalence of tuberculosis in these species in the African region, however, indicates that they may not be significant in transmis-

Human to animal transmission through aerosols is well documented and patients with pulmonary tuberculosis pose danger to animals [50]. Humans with urogenital tuberculosis represent a source of infection for animals through contamination of pastures with urine. In Ethiopia, the traditional practice of spiting chewed tobacco into mouths of livestock as anti-parasitic treatment is a potential source of infection

Male animals were more significantly affected by than female animals while Bos

The primary source of infection by MOTTs is presumably the environment [16], and although, the specific source of individual infections may not be easily identified, and the route of infection may be deduced from the localization of

Animals exposed by ingestion of contaminated feed or water often develop primary foci in lymph nodes associated with the intestinal tract, while aerosol exposure leads to the involvement of the lungs and associated lymph nodes. In case of respiratory infection, the mucociliary clearance in the upper respiratory passages may prevent infection in some exposed animals [52]. In the bronchi, the organism penetrates the mucosa and are trapped and phagocytosed in the bronchial and mediastinal lymph nodes. In the lungs, the bacterial are phagocytosed by alveolar macrophages. In case of oral infection, the organism presumably penetrates the bucal or intestinal mucosa and, via the lymphatics, reaches the phagocytes in the draining lymph node. The phagocytosis causes a localized inflammatory reaction and recruitment of mononuclear cells from neighboring blood vessels. The cellular response results in the accumulation of large number of phagocytes leading to the formation of the granuloma or the tubercle that characterizes the disease [36, 47]. The granuloma consists of infected macrophages surrounded by epithelioid cells,

granulocytes, lymphocytes, and later, multinucleated giant cells [53].

Mycobacteria are facultative intracellular pathogens, and survive and multiply within the hosts' phagocyte. The ability of the organism to survive intracellular within macrophages involves interfering with the development of the phagosome into a degradative vesicle. It is thought that the organism prevents the phagosome from maturing and fusing with lysosomes to form the phagolysosome. The mycolic acids of the organism are thought to play a role in blocking this phagosome maturation [54, 55]. Some components of the lipid layer, such trehalose dimycolate, may cause death of macrophages by direct cytotoxicity [52]. The Mycobacterium survival and multiplication within the phagosomes eventually destroys the macrophage. When entering into the death phase, infected macrophages release mycobacterial antigens, which are engulfed by uninfected dendritic cells, processed and subsequently presented, via major histocompatibility complex class I, to CD8+ T cells. The cellular hypersensitivity that develops, contributes to cell death and tissue destruction resulting in caseous necrosis. In some instances, liquefaction and cavity formation occur as a result of enzymatic action on proteins and lipids, and the organism multiplies uncontrolled in these cavities. Rapture of the cavities into the bronchi allows aerosol spread of the bacilli. Dissemination by bacteria-containing macrophage may occur through vascular and lymphatic channels to form lesions

indicus (zebu) have been found to be more resistant than Bos Taurus (Exotic breeds). At the herd level, herd size increases infection due to increased exposure

and introduction of new animals into a herd is a risk factor [51].

sion of disease to cattle [48, 49].

Diseases Caused by Bacteria in Cattle: Tuberculosis DOI: http://dx.doi.org/10.5772/intechopen.82051

with M. tuberculosis [3].

granulomas.

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6. Pathogenesis
