Somewhere beneath England's rolling fields, there's a badger with a price on its head. Sometime in the next two weeks, it will likely become the first of hundreds to be shot dead as part of a pilot cull licensed by the UK government to curb the spread of bovine tuberculosis to cattle ? despite the fact that the badgers are protected under UK law.
Farmers in England and Wales are keen to get on with the controversial cull. They have seen the annual slaughter of cattle with bovine TB soar from 6000 in 1998 to 34,000 in 2011, and have long argued that badgers are at least partly responsible. They infect cattle by contaminating pastures, feeding areas, and even the air with Mycobacterium bovis ? the bacteria that causes TB both in badgers and in cows.
Now, for the first time, an independent scientific group has presented evidence in support of a cull ? five years after it suggested that culling would not work.
Worst nightmare
James Small's farm in Somerset has just reopened after a 6-month lockdown triggered when one of his cows tested positive. He says that bovine TB is every cattle farmer's worst nightmare ? both in the UK and elsewhere (see "Possum purge", below).
"It's terrifying. Until the disease has really progressed in your cows, there are no visible signs," he says. "We got the all clear in September after tests for the herd were negative for the necessary 120 days, but the test days were really stressful, not knowing what the vets would find."
Small is relieved that one of two pilot studies to evaluate badger culling is set to go ahead, although his farm lies outside both of the proposed field-trial areas. Others are appalled by the decision. Queen guitarist Brian May launched an online petition to stop the cull, which has amassed 150,000 signatures to date.
Perturbing results
At first glance, the new pilot studies appear to fly in the face of previous science. In 2007, interim conclusions of the Randomised Badger Culling Trial (RBCT) ? a ?50-million experiment to assess the merits of a badger cull ? suggested that culling would not work. Killing badgers reduced the number of infected cattle herds within the RBCT study area by some 23 per cent compared with unculled areas, but these gains were offset by a 24 per cent rise in herd losses in a 2-kilometre-wide ring surrounding the culled area.
Researchers called this phenomenon the "perturbation effect". Infected badgers in the culling area fled to the sanctuary of the surrounding unculled zone, taking TB with them. So strong was the perturbation effect that the increased herd losses in the peripheral area effectively cancelled out gains within the culled area.
In fact, the 2007 conclusions suggested that just 14 herd infections would have been avoided after a sustained badger cull covering 1000 square kilometres of farmland for five years. But continued monitoring of the same sites where the RBCT took place has changed the picture, strengthening the justification for culling after all.
Persistent benefits
Christl Donnelly, an epidemiologist at Imperial College London, was a member of the team that performed the original 2007 analysis. She has periodically collected data from the study region since 2006. The improvements seen within the study area have persisted.
Between 2006 and 2011 there were 28 per cent fewer TB infections there than might otherwise have been expected. What's more, the boost seen in TB levels in the unculled outer ring was not sustained. In fact, between 2006 and 2011 there were 4 per cent fewer TB cases than expected from controls within the outer ring (PLoS One, doi.org/bb936n).
Armed with the new data, scientists advising the UK government concluded that culling over four years in a hypothetical area of 150 square kilometres ? killing an estimated 1000 to 1500 badgers ? could achieve a net reduction of herd infections of around 16 per cent within nine years. This, they calculated, equates to preventing 47 out of 292 TB infections that would result in a farm being locked down.
"The data that have accumulated have pushed us more towards a position to cull," says Donnelly. At a pivotal meeting in December 2011, scientific experts advising the UK government's Department for the Environment, Food and Rural Affairs (DEFRA) on bovine TB concluded that culling might play a role, alongside existing measures to physically exclude badgers from farms, frequently test cattle for TB and restrict movement of affected herds.
Points of view
Not everyone is convinced. Indeed, even Donnelly has reservations. "Is it worth culling so many animals for 16 per cent fewer infected herds? There, you get very different answers depending who you ask."
John Krebs at the University of Oxford headed the team that carried out the original trials. He sees problems with the new conclusions. "The pilot cull is flawed because it aims to remove 70 per cent of badgers without an accurate estimate of the starting number," he says.
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