1. Introduction

Tuberculosis in cattle is of serious public health as well as economic concern worldwide but more so in developing world. The disease is a zoonosis, transmitted from animals to humans mainly through the consumption of raw animal products especially milk. Human infections are therefore prevalent in communities with poor food hygiene and unsanitary cultural practices [1]. The resultant disease manifestation is largely similar to the human-type tuberculosis, with socioeconomic costs of stigma, reduced productivity, mortality, and cost of treatment. Rigorous control and eradication programs have drastically reduced transmission to humans in the developed world but in the developing world, it remains a serious threat to human health. Animal to animal transmission is mainly through the inhalation of infective respiratory aerosols. Production systems that involve close contact between animals promote transmission. The disease is listed under World Animal Health Organization (OIE) and therefore a restriction to trade in animals and animal products. Other costs include reduced animal productivity and the cost of control.

Since its identification in 1898, Mycobacterium bovis (later split into two subspecies: M. bovis subsp. bovis and M. bovis subsp. caprae) has been considered as the etiological agent of tuberculosis but later, other members of the Mycobacterium tuberculosis complex (MTBC) were found to cause similar infections [2–4]. More recently, species of mycobacteria hitherto regarded as saprophytic and nonpathogenic, referred to as nontuberculous mycobacteria (NTM) and more recently, mycobacteria other than tuberculosis (MOTTs) have been identified as causative agents [4, 5]. Apart from the requirement for isolation and identification of the causative for confirmatory diagnosis, these species have complicated interpretation of in vivo diagnostic tests, such as the tuberculin test, due to the expected cross-reactive immune responses [6, 7]. Some of these MOTTs have also been found to cause a variety of infections in humans and should therefore be considered potentially as zoonotic, and infestations in cattle and other animals as important and the MTBC. Many other species of animals are also susceptible to M. bovis. These include wildlife species, which constitute reservoirs of infection for domestic animals [8, 9]. Transmission to domestic animals and humans is therefore potentially an outcome of humanwildlife conflict. With such a variety of mycobacteria species, now associated with tuberculosis in cattle, perhaps the etiological term mycobacteriosis, rather than the pathological term tuberculosis, should be more applicable. This chapter will explore the etiology, epidemiology, pathogenesis, pathology, diagnosis, public health importance, and control of tuberculosis in cattle. It is expected that the chapter will be found useful by veterinary students, tutors, animal health service providers, and researchers.

bacilli. The extract was initially tried as a vaccine, but later shown to have diagnostic potential to detect infected animals. The tuberculin skin test for animals was thereafter developed [10]. The development of the skin test for humans was then carried out by Von Pirquet and Mantoux in 1907–1908 [13]. In the developed world, bovine TB eradication programs involving herd testing and culling of reactors and pasteurization of milk has largely eliminated the spread of bovine TB. The disease, however, remains a serious public health problem in many developing

The genus Mycobacterium is the only genus in the family Mycobacteraceae in the order Actinomycetales, which includes other mycolic acid-containing genera, namely Nocadia, Rhodococcus, Gordonia, and Tsukamurlla. Currently, the genus comprises of over 150 species and 13 subspecies [15, 16]. Within the genus, classification is based on several factors including growth rate and pathogenicity. Based on pathogenicity, it can be classified into two groups: tuberculous and nontuberculous mycobacteria, the latter also referred to as mycobacteria other than tuberculosis (MOTTs). A refined classification on this basis groups the genus into obligatory pathogens, potentially pathogenic (opportunistic) and saprophytic or ubiquitous microorganisms [17]. Obligatory pathogens belong to Mycobacterium tuberculosis complex (MTBC) group that comprise Mycobacterium bovis subsp. bovis, M. bovis subsp. caprae, M. tuberculosis, M. africanum, M. bovis BCG, M. canetti, M. microtti, M. pinnipedii, and M. leprae [18]. All MTBC species have identical 16S rRNA sequences and a 99.9% similarity at nucleotide level, and may even be considered subspecies, but differ significantly in their host range [19]. The potentially pathogenic mycobacteria, represented by the Mycobacterium avium complex (MAC), consists of closely related species and subspecies, which include, among others, M. avium subsp. avium, M. avium subsp. paratuberculosis, and M. avium subsp. hominissuis. The potentially pathogenic species are found in the environment as well as in the susceptible hosts and cause disease mainly in hosts with compromised immunity [20]. Saprophytic mycobacteria are the largest group found in the environment. Some, such as M. kansasii, M. asiaticum, M. interjectum, M. szulgai, M. fortuitum, M. celatum, M. ulcerans, M. smegmatis, and M. septicum have been associated

On the basis of growth rate, the genus is classified into slow and rapidly growing species, with rapid-growers being those that produce grossly visible colonies in less than 7 days and slow-growers taking over 7 days. Slow-growing species are more commonly associated with pathogenicity than the fast-growing

In cattle and other ruminants, tuberculosis is caused mainly by the obligate pathogen Mycobacterium bovis subsp. bovis but infections by Mycobacterium bovis subsp. caprae, Mycobacterium tuberculosis and Mycobacterium africanum also occur [2–4]. In Central Europe, M. bovis subsp. caprae is the major cause of tuberculosis in cattle [23, 24]. The disease caused by M. bovis subsp. bovis and M. bovis subsp. caprae is commonly referred to as bovine or zoonotic tuberculosis. Although not as widely as zoonotic tuberculosis, MOTTs infections have been reported in cattle exhibiting granulomatous lesions identical to those caused by the MTBC complex

countries [14].

4. Etiology

group [22].

[6, 15, 16].

65

4.1 Classification of mycobacteria

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

with diseases in humans and animals [21].
