Abstract
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.
Highlights
Bovine TB is a chronic disease of animals caused by infection with the slow-growing, obligate intracellular bacterium Mycobacterium bovis [1, 2]
The risk factors that have been most consistently identified in relation to bovine TB, in recent United Kingdom (UK) and Ireland studies include historic incidence, farm area, cattle movement, occurrence of TB on contiguous premises and/or the level of bovine TB in surrounding areas, and herd size (Table 1) [54]
Other factors identified in some studies include indicators of badger density/activity, use of multiple premises, housing type, herd type, farmland habitat, fertiliser usage, mineral deficiencies, and use of silage clamps (Table 2)
Summary
Bovine TB is a chronic disease of animals caused by infection with the slow-growing, obligate intracellular bacterium Mycobacterium bovis [1, 2]. Whilst it is important to view bovine TB as an infectious disease which requires preventive as well as control measures, M. bovis infection in cattle rarely presents as clinical disease. More commonly it appears as apparently healthy animals responding to an immunological test based on tuberculin, an entirely different scenario to that which existed when control programmes were first introduced [20]. Infection appears to be relatively poorly transmitted between cattle in most, but not all, circumstances
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