What about the role of wildlife?
M. bovis can infect a wide range of wildlife species, in some cases these are ‘dead end’ hosts incapable of transmitting the disease further. However, in some cases wildlife can act as a ‘maintenance host’ or wildlife reservoir for the disease and a potential source of infection for cattle. In the UK and Ireland the European badger (Meles meles) is the principal wildlife reservoir for the disease and is implicated in disease transmission to cattle, although in some localised areas it is possible that deer are also involved. Options for managing the disease in badgers include culling, vaccination or biosecurity measures.
Research on badger culling in the UK has shown that culling badgers can reduce TB in cattle, if the culling is efficient at removing animals (>70% reduction) and is done on a large scale for a long period of time (4 years or more). Levels of TB reduction observed inside ‘proactive’ areas in the RBCT (randomised badger culling trial) were 19-32% (over a 10 year period, although ‘perturbation’ of badger populations around cull areas may reduce this benefit) suggesting that culling alone is unlikely to solve the problem of TB in cattle. It is unclear whether the current industry led culls will achieve similar, higher or lower levels of reductions in cattle TB. Vaccination of badgers with the BCG vaccine has been shown to reduce the likelihood that badgers become infected and also slows the progression and development of the disease. However, the effect of badger vaccination on cattle TB is unclear. For a great summary of the TB science evidence base read Godfray et al. 2013.