October 22, 2013
Important Link Between Badger Social Networks And TB Infection
April Flowers for redOrbit.com - Your Universe Online
The social lives of badgers are related to their risk of infection with bovine tuberculosis (TB), according to a new study from the University of Exeter and the AHVLA's National Wildlife Management Center.
"In wild animals, just as in humans, social networks are very important for disease transmission," said Robbie McDonald of the University of Exeter. "When management changes stable networks, the results for disease control are often counterintuitive and unexpected."
The research team equipped more than 50 wild badgers with electronic proximity collars that automatically tracked their social contacts. Exeter PhD student Nicola Weber, working with colleagues at the National Wildlife Management Centre at Woodchester Park in rural England, used the data from the collars to build a network of contacts across the population and analyzed patterns of infection. Weber found that uninfected badgers were more well-connected to their own groups than the infected badgers. The infected animals, however, form important links for the flow of infection between groups. The findings, published in Current Biology, suggest that the unusual social arrangement may stabilize the spread of TB infection across the entire population.
McDonald said, "This study has revealed an important link between social networks and TB infection. Infected animals were likely to be less important for spread within groups while at the same time being more important for spread between groups."
"Social stability is thought to mitigate disease spread, perhaps by maintaining the distinctive position of these individuals. Culling badgers perturbs social structures and we think our findings may help understanding of so-called 'perturbation', where culling has been linked to increases in TB in badgers. Curbing TB infection in wildlife remains a challenge. Vaccination has the potential to disrupt disease flow, without perturbing social network structures," said McDonald.
The team calls the infected animals "spread capacitors." They are passive components in the network that can hold and discharge infection, however they tend to stabilize flow. "That's in contrast to the more familiar notion of 'super-spreader' individuals that are thought to spread infection disproportionately because of their high connectedness in a network," McDonald explained.
According to the study, badger management efforts will be most effective when they maintain the stability of the badger population and refrain from disturbing the social networks. The long term implication might be that it is more effective to vaccinate infected badgers rather than cull them from the networks.
"The good news is that vaccination does not disturb social structure," McDonald says. "The sort of social structure we have observed -- where relatively few individuals might be responsible for disease spread -- lends itself to vaccination and could lead quite rapidly to herd immunity."
In the UK and Ireland, TB infections in cattle are a major health challenge. More than 8 million tests were conducted on cattle in 2012, and 38,000 cattle were slaughtered to control the spread of the disease. The testing, and the compensation for destroyed cattle, costs the UK taxpayer around $161 million USD.
This study has implications beyond the social networks of badgers. The analyses used for this study is similar to these used in humans, meaning that these same techniques can be used to learn about how infection is transferred in a range of behaviorally complex hosts, including humans, livestock and wildlife.