Bovine tuberculosis

 CAB International 2018. Bovine Tuberculosis

122 (eds M. Chambers, S. Gordon, F. Olea-Popelka, P. Barrow)

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9.1 Introduction

Mycobacterium bovis is able to infect a wide vari-
ety of domestic and wild animals, including
humans (O’Reilly and Daborn, 1995). M. bovis is
a member of the Mycobacterium tuberculosis
complex (MTBC), which also includes M. tuber-
culosis, M. bovis, M. africanum, M. microti, M. cap-
rae, M. canetti, M. pinnipedii and M. mungi
(Rodriguez-Campos et al., 2014).
Bovine tuberculosis is the infectious disease
of cattle caused by M. bovis or M. caprae
(Domingo et al., 2014). The disease follows a
chronic course with the formation of a granulo-
matous, caseous and necrotizing inflammatory
process affecting mainly the respiratory tract
(lungs and draining lymph nodes) or other loca-
tions, including the gastrointestinal tract and
secondary lymphoid organs.
Once the bacteria enter the host, the infec-
tion can remain subclinical for long periods of
time. The lesions will start to form, and can
develop into a localized or generalized form of
the disease affecting multiple organs. The route
of infection will determine the location and
spectrum of the lesions observed in bovine
tuberculosis (Domingo et al., 2014). The most
common route of infection is via inhalation of
droplet nuclei or other aerosol material, causing
lesions in the upper and lower respiratory tract,
including the lungs, and the associated

lymphoid tissues (Neill et al., 1994, 2001).

Depending on the infection dose, M. bovis may

also induce typical lesions in the upper respira-

tory tract mucosa and the retropharyngeal

lymph nodes (Cassidy et al., 1999). Interestingly,

animals experimentally infected intratracheally

with M. bovis in addition to those that are

infected naturally can also show lesions in a

variety of lymph nodes in the head and neck

area (Dean et al., 2014, 2015; Ameni et al.,

2017; Salguero et al., 2017).

The tonsils are an interesting site of infec-

tion by M. bovis, with a significant number of

animals naturally and experimentally infected

with M. bovis showing either lesions or viable

bacteria isolated by culture in this organ ( Cassidy

et al., 1999; Liébana et al., 2008).

If the pathogen enters the organism via

ingestion of contaminated pasture, water or

feed, a gastrointestinal form of the disease will

be established with frequent lesions in the mes-

enteric and hepatic lymph nodes (Menzies and

Neill, 2000). Other routes of infection (e.g. geni-

tal, intramammary or transplacental) can be

also observed but with very low frequency due to

the epidemiological situation of most countries

that have active control or eradication pro-

grammes (Domingo et al., 2014).

Bovine tuberculosis continues to be a very

important disease for cattle farming and as a

public health concern because of its zoonotic

9 The Pathology and Pathogenesis of

Mycobacterium bovis Infection

Francisco J. Salguero*

Department of Pathology and Infectious Diseases, School of Veterinary Medicine,

University of Surrey, Guildford, UK