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Cattle not helped by UK badger cull

Latest findings show that killing badgers causes more cattle tuberculosis than it prevents

By | December 15, 2005

Research published this week could help resolve the thirty-year UK controversy over the role of European badgers Meles meles in the spread of bovine tuberculosis (TB). One paper, published in Nature, provides strong evidence that culling badgers -- which can carry the agent that causes bovine TB -- actually exacerbates the problem by raising the incidence of TB in cattle living nearby. The results help to clarify contradictory results on whether culling badgers can control bovine TB, but the Department for Environmental Food and Rural Affairs (DEFRA) announced today that they are opening the possibility of large-scale cull to public opinion.

"We found that a single culling policy -- that of widespread and repeated culling of badgers -- yielded both a reduction of 19% in TB incidence in cattle within the culled area and an increase of 29% in TB incidence in cattle in the surrounding area," Christl Donnelly, lead author of the Nature paper, told The Scientist. She is based at the Department of Infectious Disease Epidemiology, Imperial College London, UK.

These findings demonstrate that badger culling has an overall negative effect on TB rates in cattle, according to Rosie Woodroffe at the University of California, Davis, lead author of an accompanying paper in the Journal of Applied Ecology. Woodroffe said the findings should signal a new direction in TB control policy. "I would imagine that future studies will be likely to focus on other approaches to TB control, rather than culling," she said.

Badgers were implicated in the spread of bovine TB during the 1970s.These latest findings result from the Krebs report, a series of government sponsored experiments during which more than 30,000 badgers were culled despite their legally-protected status. The scale of the operation has angered conservationists, who have called for a better understanding of badger behavior rather than their wholescale destruction. "Only a fraction – less than 1% – of badgers are infectious," a spokesman for the Badger Trust told The Scientist. The current UK population is estimated to number approximately 250,000 animals.

According to Woodroffe, the findings suggest "highly complex transmission dynamics." In areas where culling took place, badgers ranged over greater distances. Culling appears to disrupt social groups, and the increased mobility potentially leads to greater contact – and hence disease transmission – with cattle, she said. These findings also help explain why previous research showed that TB rates in cattle fell after researchers practically eradicated badgers, but increased after local culling. "Small-scale culling, such as that which might be advocated as a compromise between conservation and farming concerns, or by farmers acting illegally, is actually the worst possible approach in terms of controlling infection in cattle," Woodroffe told The Scientist.

The findings come as no surprise to the University of Bristol's Stephen Harris, an expert on UK mammals. "It's nice to confirm what is already considered a truism," he said, "but it's depressing to still be discussing the self-evident after so long." Harris, who was not involved in either study, also pointed out that the issue of bovine TB is politically charged. "Farmers are now paying the price for not imposing stricter controls on the movement of cattle," he said.

Peter Hudson, a wildlife epidemiologist at Penn State University, applauded the "courage" shown in carrying out the controversial experiment, but said that the focus must now shift. "We need to concentrate on the variance rather than the mean," he said. Hudson, who was not involved in the studies, went on to explain that only a small number of badgers are likely to be responsible for the majority of cattle herd breakdowns, and that future research must aim to single those animals out. "We're going to have to find out just which animals are doing the infecting and when. At the moment, we don't even know what the process of transmission is."

Nevertheless, in a statement today, DEFRA announced a 12-week public consultation on the possibility of large-scale badger culling in areas of high TB among cattle. Despite the evidence presented in Donnelly's and Woodroffe's papers, the Animal Health and Welfare Minister Ben Bradshaw said that "there is still enough scientific uncertainty - in particular about different culling strategies - to make it important to consult on the principle as well as the method of badger controls."

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