on 02 November, 2015

Leading experts say latest badger culls will not stop TB

Two leading Scientists, Christl A. Donnelly Imperial College London, and Rosie Woodroffe, Institute of Zoology, London reveal in an article, published today for www.nature.com magazine that the latest badger culls unlikely to stop TB. Two months ago, the government advice body Natural England approved further licensed badger culls in parts of the United Kingdom in 2015. The aim is to reduce local badger densities by at least 70% to stop the

spread of bovine tuberculosis (TB) to cattle. This figure is critical because reductions of less than 70% can, paradoxically, increase TB transmission rates (see H.C.J. Godfray et al. Proc. R. Soc. B 280, 20131634;2013).

On the basis of current badger population estimates, we calculate that these culls are unlikely to achieve the necessary reduction.

The latest minimum cull numbers derive from the lower 95% confidence bounds on population size estimates. For example, licensees in part of Dorset are required to kill at least 615 badgers in a population that are estimated to contain somewhere between 879 and 1,547 animals (95% confidence interval). Killing this number would give an estimated population reduction of between 39.8% and 70% (95% confidence interval).

Equivalent confidence intervals for the 2015 Somerset and Gloucestershire culls are, respectively, 50.8–70% and 54–70% relative to the baseline population estimates. It is, therefore, unlikely that a 70% or greater reduction can be attained by these minimum cull numbers, assuming that the population estimates are accurate.

In our view, populations that are either reduced by greatly more than 70% or left undisturbed (and potentially vaccinated) are likely to offer better prospects for the control of cattle TB. The choice depends on a range of epidemiological, economic, social and ecological factors.

Authors; Christl A. Donnelly Imperial College London, UK. Rosie Woodroffe Institute of Zoology, London