October 23, 2012

expert reaction to announcement that the badger cull is due to be delayed

The government announced that the planned badger cull in Gloucestershire and Somerset, due to begin this year in attempt to reduce the prevalence of bovine TB, has been postponed until summer 2013 because badger numbers are higher than was previously thought.

Prof Rowland Kao, Wellcome Trust Senior Research Fellow and Director of the Boyd Orr Centre for Population and Ecosystem Health at the University of Glasgow, said:

“It’s going to be difficult to determine what, if any, short term effect the delay is going to have. Defra is already announcing more severe restrictions to cattle in the wake of a bTB breakdown (seehttp://www.defra.gov.uk/ahvla/2012/10/19/19-october-defra-introduces-tighter-control-measures-in-england-to-tackle-the-spread-of-bovine-tb/)- if these measures have the intended  impact on breakdown incidence, any changes in herd incidence will be hard to attribute to any one effect.

“Though estimates of overall badger densities are hard to come by, longer term, if they are increasing, then this could contribute to increases in higher incidence of bTB in cattle.

“It’s unlikely that the increased numbers of badgers will drastically change the expected incidence in cattle; what matters is the relative population density when comparing across regions – if the same underestimates apply quite broadly then it simply means that higher densities are required to see the observed incidence in cattle. Higher densities will mean more effort will be expended and costs may be higher to achieve given density reductions, but we don’t really have a good idea of the relationship between changes in badger density and cattle herd incidence as they occur in different regions. A paper from a collaboration I was involved with (‘Risk factors for bovine tuberculosis at the national level in Great Britain’ by Bessell, Orton, White, Hutchings and Kao in BMC Vet Research, 2012) does show that when comparing across high incidence areas in GB, badger density estimates are correlated with higher cattle herd incidence.”

“A good vaccine obviously has its attractions, but a large scale implementation of either a cattle or badger vaccine is likely to be a long way off; for cattle the lack of a test that distinguishes between vaccinated and infected cattle is a key problem and for badgers there is no efficient delivery system for a large scale implementation.  Plus we’ve no good field evidence for the required efficacy of a vaccine for either species.”

Prof Christl Donnelly, Professor of Statistical Epidemiology, MRC Centre for Outbreak Analysis and Modelling, Imperial College London, said:

“The badger cull is being delayed in part because it has been discovered that there are more badgers in the cull areas than had been planned for.  Scientists do not have a validated model to predict how a higher badger density would change the risks to cattle. The immediate impact of the increased badger numbers is that the requirement to remove a high proportion of badgers costs more if badger density is high and the contractors are being paid per badger culled.

“In the next month, I will be doing further updates to estimate the longer term effects of (repeated, widespread) badger culling, but the benefits estimated from the culling trial have been diminishing as the last culls get longer and longer ago, so these further analyses are unlikely to radically change anyone’s views on whether badgers should be culled.

“Vaccine development is ongoing for both cattle and badgers. I am not in a position to predict when an oral badger vaccine would be available but an injectable one is already available and is already being used in Wales.”