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Badgers' behavior could thwart TB control policy

September 12, 2003 By John Whitfield This article courtesy of Nature News.

Animals mingling more after culling may increase disease transmission.

Changes in badgers' social life after culling could undermine efforts to control bovine tuberculosis (TB), British ecologists have found. The surviving badgers bunch up, causing groups' territories to overlap more, possibly promoting disease transmission.

Bovine TB is a serious agricultural problem. More than 15,000 British cattle have been slaughtered this year because of the disease, nearly two-thirds of them in the west of England. The government pays out millions of pounds in compensation to farmers.

Badgers (Meles meles) carry the disease, although whether they infect cows is still controversial. Since the early 1970s, the British government has culled animals in an effort to control bovine TB. But the number of cases in cattle has been rising since the early 1980s.

Undisturbed badger populations divide the landscape into territories around their setts. There is little mixing between groups, and so less potential for animals to infect each other. It's not known what determines the disrupted badgers' response to culling.

Philip Riordan, of the University of Oxford, and his colleagues studied an area of Gloucestershire, in western England, around a farm with a history of bovine TB. In 1995, about 40% of the badgers in this area were killed. Wildlife managers hope that, by thinning out populations, they can prevent animals from infecting each other.

Over the ensuing four years, badgers away from the culled groups expanded their territories, leading to more interaction between groups. The population became more clumped in a small area of the study site.

"Within those clusters the risks of disease transmission would be higher," Riordan told this week's annual meeting of the British Ecological Society in Manchester. Bovine TB reappeared in the badger cluster in 2000.

Imagining that reducing population density will have a simple effect on disease transmission is far too simplistic
Owen Petchey
University of Sheffield

The study shows the importance of carrying out studies to test policy decisions, says ecologist Owen Petchey of the University of Sheffield, UK. "Imagining that reducing population density will have a simple effect on disease transmission is far too simplistic," he says.

In 1998, Britain began a large-scale experiment on the effects of badger culling on bovine TB. The trial is expected to run until 2006. Riordan's team is looking at how badgers respond in different places, and under different culling regimes. "Our results so far are from just one site - we need to generalize," he says.

Other researchers are working on developing TB vaccines that could be administered to cattle or badgers.


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