Badger culls must be based on sound science, researchers say

Researchers have urged policy makers to field test any new strategy to control the spread of TB between badgers and cattle. The recommendation comes in a new study published in the British Ecological Society’s Journal of Applied Ecology that reveals evidence of a close spatial association between bovine tuberculosis (TB) in badgers and cattle.

Using data from the Randomised Badger Culling Trial, Dr Rosie Woodroffe and colleagues from the Independent Scientific Group on Cattle TB looked at local geographical associations between TB (Mycobacterium bovis) infection in badgers and cattle. They found that TB infection occurs in clusters in both badgers and cattle and these clusters are spatially associated on a scale of 1-2 km.

The study found that most TB-infected badgers are caught within 1km of infected cattle herds, while uninfected badgers live further from infected cattle, and that badgers and cattle carrying the same strain of TB live especially close together. “This suggests that TB is indeed transmitted between the two species – but this could be because cattle give TB to badgers, as well as badgers giving TB to cattle,” the authors say.

As well as providing the first evidence for the spatial association of TB infection in badgers and cattle at this scale, the results offer important insights into the kind of ecological evidence that needs to be gathered for effective TB control strategies to be developed in what continues to be a controversial field.

The close association of cattle and badger TB infection found by this study could lead to the suggestion that localised badger culling should reduce the risk of TB infection in cattle, yet experimental reactive culls have not been effective. “Curiously, the research suggests that past policies of culling badgers living close to infected cattle might have been expected to work – yet TB incidence in cattle rose when these policies were in place and a more recent experiment showed only negative effects of such reactive culls. This could be because culling may have disrupted clusters of infection in badger social groups, spreading the disease over wider areas. This difference between the expected effect of a culling policy and its actual effect means that policy makers must field test any new policy before applying it nationally,” the authors say.