Mycobacterium bovis, the bacterium that causes bovine tuberculosis (TB), has been detected in about one-fifth of a sample of 94 road-killed badgers collected between 2014 and 2015 in the UK county of Cheshire, according to a study in Scientific Reports. Cheshire was thought to be on the edge of the bovine TB epidemic in the UK, but has seen an increase in the incidence of TB in cattle since 2010. The authors note that their study does not determine the causes of this expansion.

Elsa Sandoval, Malcolm Bennett and colleagues studied road-traffic killed badgers, collected in Cheshire through a network of local farmers, veterinarians, wildlife groups and government agencies between 2014 and 2015. M. bovis was found in 21% (20 out of 94) of the badger carcasses. Conversely, in road-killed badger surveys conducted in Cheshire between 1972 and 1990, only one badger out of a sample of 389 was found to carry the bacterium (0.26%).

The prevalence of M. bovis in badgers in Cheshire was found to be similar to the estimated prevalence of 18% and 20% in Worcestershire and Gloucestershire respectively, which are both considered ‘high-risk’ counties for cattle infection, suggesting the spread of the epidemic outside of the South West of England.

Although the results suggest that both badgers and cattle may be part of the same geographically expanding epidemic, the authors emphasize that the direction of any cross-species transmission - whether the badgers infect the cattle or vice versa - cannot be determined. Further studies are needed to achieve a fuller understanding of the transmission of M. bovis in areas such as Cheshire.