Badgers, bovine TB, culling…it’s mostly bad news

TB testing. Image from Farmers Weekly
TB testing. Image from Farmers Weekly

New Epi-Connect publication

Bovine tuberculosis is an important disease affecting the UK livestock industry. Controlling bovine tuberculosis (TB) is made more complex by the presence of a wildlife host, the Eurasian badger, Meles meles. The Randomised Badger Culling Trial (RBCT), which was designed by the Independent Scientific Group on Cattle TB (ISG) and ran between 1998 and 2006, investigated how bovine TB spread between cattle, badgers and other wildlife. The trial took place in 30 areas of approximately 100km2  , grouped into 10 sets of three, known as ‘triplets’.

The RBCT. http://webarchive.nationalarchives.gov.uk/
The RBCT. http://webarchive.nationalarchives.gov.uk/

Repeated large-scale (“proactive”)badger culls implemented in the Randomised Badger Culling Trial (RBCT) were associated with decreased cattle risks inside the culling area, but also with increased bovine TB risks up to the 2km outside the culling area. Localised (“reactive”) badger culling was shown to increase the incidence of bovine TB inside the culling area (Donelly et al. 2006).

In an open-access paper recently published with PLOS ONE, Jon Bielby, Christ Donnelly, Rosie Woodroffe and I used used a matched-pairs case-control study design to the spatial scale over which reactive badger culling had its biggest impact. We found that reactive badger culling significantly increased the risk of bovine TB at distances of 1-3km and 3-5km from the culled area, and that no such association existed over shorter distances (<1km).

Our findings are consistent with the spatial scale of changes to badger dispersal (up to and over 5 km) in response to repeated culling (Pope et al. 2007), and the increase in badger TB infection prevalence observed in response to localised reactive culling (Woodroffe et al. 2009).

We show that localised badger culls had significant negative effects, not on the land on which culling took place, but, perhaps more importantly, on adjoining lands and farms, highlighting how relatively localised, moderate reductions to badger density can lead to landscape-level effects of considerable size. We stress the importance of considering the broader impacts within and upon the farmed landscape when considering implementing badger culling as a method of controlling the spread of bovine TB.

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