Bovine tuberculosis (bTB; Mycobacterium bovis) is a bacterial infection of cattle that also affects certain wildlife species. Culling badgers (Meles meles), the principal wildlife host, results in perturbation of the badger population and an increased level of disease in cattle. Therefore, the priority for future management must be to minimize the risk of disease transmission by finding new ways to reduce the contact rate among the host community. At the farm level, targeting those individuals that represent an elevated risk of transmission might prove to be effective. At the landscape level, risk mapping can provide the basis for targeted surveillance of the host community. Here, we review the current evidence for bTB persistence in Britain and make recommendations for future management and research.
Wildlife hosts for bovine tuberculosisMany infections of humans and their livestock are able to cross-infect multiple host species [1]. The presence of infections within a multiple-host community can complicate attempts to reduce disease [2,3], not only because of varying resistance to infection between the different host species but also because of ecological and behavioural differences.Bovine tuberculosis (bTB; Mycobacterium bovis) persists in various countries in the developed world. In some of these countries (including Britain, Ireland and New Zealand), the presence of additional wildlife hosts for the infection -principally Eurasian badgers (Meles meles) in the UK and Ireland, and brush-tailed possums (Trichosurus vulpecula) and ferrets (Mustela putorius) in New Zealand -is thought to have contributed to the persistence of the disease in cattle, despite considerable investment in culling programmes to reduce the populations of these wildlife hosts. Badgers are particularly well suited as a host for bTB because they are a group-living animal. They exhibit a range of social structures, with social group size varying between two individuals in Poland and 25 individuals in Britain, and group territories ranging from 0.14 km 2 in Britain to 14 km 2 in Poland and Finland [4].In Britain, the total economic costs associated with bTB between 2004 and 2011 are expected to reach £1 billion [5]. A test-and-slaughter strategy to detect and remove bTB-infected cattle from British herds had all but eradicated bovine bTB in a large part of Britain by the 1970s, and persistent infection was limited to distinct areas in southwest Britain. Since that time, badgers have been implicated increasingly in the persistence and reemergence of bTB as the disease has spread once more into new areas, both within southwest Britain and beyond.A large-scale field trial, the Randomized Badger Culling Trial (RBCT), was initiated in 1999 to determine the extent of badger involvement in bTB in cattle and the effectiveness of culling badgers in reducing bTB infection in cattle [6,7]. The field trial showed that badger culling over 100-km 2 areas could result in a decrease in cattle bTB inside these areas, with effectiveness increasing with distan...