A bovine TB control strategy under consideration risks spreading the disease rather than supressing it, according to researchers who predict that culling badgers which test positive for TB could increase the movement of remaining badgers, potentially infecting more cattle with the disease.

The paper PNAS says that small-scale, selective culling may have the same effect on badger behavior as the Randomised Badger Culling Trial, where the removal of large numbers of animals led to expanded badger ranging. The Test-Vaccinate/Remove (TVR) pilot will carry out live TB tests on badgers, aiming to vaccinate healthy animals and cull infected ones. However, the test does have its limitations. In a previous study, only 49 per cent of badgers later shown to be infected tested positive in the live test. This means many badgers carrying TB could be missed.

To predict the impact of the TVR pilot on the remaining badgers, the researchers analyzed badger movement in 826 territories where small-scale culling took place between 1986 and 1998. 

Their results show that removing a small number of badgers from a social group led to increased dispersal and expanded ranging of remaining badgers, more frequent immigration of badgers from outside the group, lower genetic relatedness of individuals within a group, and an elevated prevalence of the bacterium that causes bovine TB.

Prof. Rosie Woodroffe, Senior Research Fellow at
Zoological Society of London
said, "TVR sounds appealing because only infected badgers are killed. Unfortunately our findings suggest that the planned TVR pilot could alter badger behaviour in ways which risk exacerbating the bovine TB problem, rather than controlling it. This is one reason why ZSL is exploring alternative options to reduce transmission between badgers and cattle."

The researchers recommend that if the TVR pilot goes ahead, then intensive monitoring of badger behavior should be put in place, and stopping rules enforced if significant changes are observed. 

Dr. Jon Bielby, Research Fellow at 
Zoological Society of London
said: "Our research is the first to look at the effects of removing small numbers of badgers from social groups. The results reinforce the need to fully understand the consequences of methods to control the spread of bovine TB before we embark on them. Otherwise we risk complicating what is already a very complex issue."