Bovine tuberculosis

 CAB International 2018. Bovine Tuberculosis
(eds M. Chambers, S. Gordon, F. Olea-Popelka, P. Barrow) 191

* Email: [email protected]

13.1 Introduction

Bovine tuberculosis (bovine TB) is a zoonotic

infection in cattle caused by the intracellular

bacterium, Mycobacterium bovis that belongs to

the Mycobacterium tuberculosis complex (MTB

complex), a group of related mycobacteria that

cause TB in mammals. Bovine TB is the most

prevalent infectious disease of dairy cattle

worldwide (Cosivi et al., 1998), causing a con-

servative annual loss of about US$3 billion

(Palmer et al., 2007). In the USA, the eradication

programme of bovine TB uses a test-and-

slaughter strategy that cost about $38 million

between 1917 and 1992; the current pro-

grammes cost approximately $3.5–4 million

annually (Charles and Theon, 2006).

Cattle of all ages are susceptible to infection

with M. bovis; however, older animals appear to

have greater susceptibility (Mackay and Hein,

1989; Thoen and Bloom, 1995; Munroe et al.,

2000). In most cases, M. bovis infection primar-

ily leads to a subclinical disease (95%) with rapid

onset in only 5% of the exposed animals. Thus,

detection of subclinical infected animals with

progressing granulomatous infection is critical

in the control and eradication of bovine TB.

Current USDA surveillance for bovine TB is a

laborious multistep procedure involving the

caudal fold test (CFT) and the comparative cervi-

cal test (CCT) or γ-interferon release assays. The

current diagnostics are problematic: CFT lacks

specificity for M. bovis and fails to detect all dis-

eased cattle, while the γ-interferon assay is costly

and requires blood samples to be processed

within 24 hours of collection. Moreover, early

detection of subclinical infection by serological

tests is hindered, since the humoral immune

response in bovine TB occurs at a late stage of

disease progression. Early diagnosis of bovine TB

is essential to prevent substantial losses of valu-

able resources, monetary and production losses,

as well as to minimize the risk of human infec-

tion. Thus, there is a need to develop a low cost-

effective, early detection assay for bovine TB.

Host macrophages are the main site for

M. bovis infection in cattle. Infection is mainly

transmitted via aerosols that are inhaled into the

respiratory tract, and gross lesions involve gran-

uloma formation in lungs and thoracic lymph

nodes (Thoen and Bloem, 1995). The biology of

the granuloma involves intense cellular and bio-

logical activity at the site of infection leading to

‘leakage’ of RNA, DNA and proteins into circula-

tion that may serve as biomarker(s) for early

detection of bovine TB. Recent advances in

13 Biomarkers in the Diagnosis

of Mycobacterium tuberculosis

Complex Infections

Sylvia I. Wanzala^1 and Srinand Sreevatsan2,*

(^1) Department of Pathobiology and Diagnostic Investigation, Michigan State University,
East Lansing, Michigan, USA;^2 Department of Veterinary Population Medicine,
College of Veterinary Medicine, University of Minnesota, St Paul, Minnesota, USA