American kids are probably more familiar with the European badger (Meles meles) than are adults. The black-and-white-striped animals show up in classic children’s stories such as Watership Down, Fantastic Mr. Fox and The Wind in the Willows. Harry Potter fans will also recognize the badger as the symbol of the Hufflepuffs. But here in England, where I’m traveling, badgers are plenty familiar among adults, especially farmers, because the species is a reservoir for bovine tuberculosis.
Cattle infected with TB have to be killed, so farmers want to control the spread of the disease as much as possible. As a result, badgers are being culled in two areas of Somerset and Gloucestershire in southwestern England.
Whenever animals are killed, some people get angry, and that’s definitely the case here. Google “badger cull” and you come up with many sites representing groups dedicated to stopping the kills. But the argument against the action generally isn’t about saving a cute critter; they say that the culling will actually spread TB to more cattle. Pilot studies showed that this might happen. And now there’s a new study in Current Biology showing why — and it all comes down to the badger’s social networks.
The research team led by Robbie McDonald of the University of Exeter in Englandbegan by trapping 51 badgers from eight social groups in Woodchester Park, a wooded valley in Gloucestershire. They placed radio tags on the animals and released them back into the park, then tracked their moves. The researchers used that data to analyze several measures of the badgers’ social networking — how frequently they came in contact with other badgers, the distance from one badger to another and the potential for TB to spread between animals.
Twenty-one of the animals were infected with bovine TB. These badgers tended to be socially isolated from the main badger groups, the researchers found, but infected badgers helped spread TB between groups. These animals “are therefore likely to make a disproportionately low contribution within groups but a disproportionately high contribution to spread among groups,” the researchers write.
The infected badgers aren’t spreading TB willy-nilly from group to group, however. But they have that potential if the social group with which they are associated is broken up, the scientists contend. That might be what’s happening in the culls: Some badgers are killed but many are left alive (current culls are missing their targets). Without their social groups, infected badgers start moving and spread bovine TB to both badgers and cattle.
"What our study shows is that social structure is very important for the transmission of infection in wild badgers," McDonald told BBC News. "It also suggests that social stability is a good way of mitigating disease spread. So if you can intervene in a system and maintain social stability that's likely to be the best of both worlds."
The way to maintain social stability and prevent spread of bovine TB is through vaccination, McDonald says. But is vaccination of badgers any better than culling? Well, it turns out that England and Wales have inadvertently set up the perfect test. While two English counties are killing badgers, the Welsh government has chosen the vaccine route. It will be interesting to see which method better controls the spread of bovine TB.