Hindawi Publishing Corporation Veterinary Medicine International Volume 2012, Article ID 621210, 10 pages doi:10.1155/2012/621210 Review Article Herd-Level Risk Factors for Bovine Tuberculosis: A Literature Review Robin A. Skuce, Adrian R. Allen, and Stanley W. J. McDowell Veterinary Sciences Division, Agri-Food and Biosciences Institute, Belfast BT4 3SD, UK Correspondence should be addressed to Robin A. Skuce, robin.skuce@afbini.gov.uk Received 6 January 2012; Accepted 14 April 2012 Academic Editor: Jesse M. Hostetter Copyright © 2012 Robin A. Skuce et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Bovine tuberculosis (TB), caused by Mycobacterium bovis, is one of the most challenging endemic diseases currently facing government, the veterinary profession, and the farming industry in the United Kingdom and Ireland and in several other countries. The disease has a notoriously complex epidemiology; the scientiﬁc evidence supports both cattle-cattle and wildlife- cattle transmission routes. To produce more eﬀective ways of reducing such transmission, it is important to understand those risk factors which inﬂuence the presence or absence of bovine TB in cattle herds. Here we review the literature on herd-level risk factor studies. Whilst risk factors operate at diﬀerent scales and may vary across regions, epidemiological studies have identiﬁed a number of risk factors associated with bovine TB herd breakdowns, including the purchase of cattle, the occurrence of bovine TB in contiguous herds, and/or the surrounding area as well as herd size. Other factors identiﬁed in some studies include farm and herd management practices, such as, the spreading of slurry, the use of certain housing types, farms having multiple premises, and the use of silage clamps. In general, the most consistently identiﬁed risk factors are biologically plausible and consistent with known transmission routes involving cattle-cattle and wildlife-cattle pathways. 1. Introduction Bovine TB is a chronic disease of animals caused by infection with the slow-growing, obligate intracellular bac- terium Mycobacterium bovis [1, 2]. This highly adapted and “successful” pathogen has a world-wide distribution and in several countries bovine TB remains a major, costly infectious disease of cattle and other domesticated, feral and wild animal populations, including badgers, possums, deer, goats, sheep, and camelids [3–5]. Bovine TB is an OIE (World Organisation for Animal Health) listed (formerly List B) disease [6, 7]. Bovine TB aﬀects cattle health, impacts negatively on proﬁtability and trade, and can decimate years of genetic improvement towards desirable production traits [8]. It also impacts negatively on the welfare of aﬀected farming families [9]. Although eﬀectively controlled by herd testing, milk pasteurization, meat inspection, health surveillance, and BCG vaccination, transmission to humans can occur and is still considered a public health risk [10–12], although some more recent opinion considers this risk to be negligible [13]. Hence, bovine TB control is currently more concerned with trade implications. Despite sustained and costly implementation of eradica- tion programmes since the 1950s bovine TB has not been eradicated from either the United Kingdom (UK) or Ireland. Indeed, there has been a sustained and largely unexplained increase over the last 25 years in parts of the UK [14]. Consequently, bovine TB is the most complex and diﬃcult multi species endemic disease currently facing government, the veterinary profession, and the farming industry in the UK and Ireland [15, 16]. Bovine TB epidemiology, in the UK at least, is exceptionally complicated, and the relationship between evidence, uncertainty and risk has been diﬃcult to communicate [17]. It is recognised as a very signiﬁcant policy challenge and continues to be almost inevitably highly politicized [18]. Pathogenesis studies suggest strongly that the route of transmission of bovine TB is largely via the respiratory system, requiring transmission via infectious aerosols [19]. Consequently bovine TB is principally a respiratory infection and the majority of infections are thought to occur via