A long-term genetic analysis of TB, carried out in Gloucestershire and examining the spread of the disease over 25 years, found that while cattle are 10 times more likely to contract TB from badgers than the other way round, the far greater likelihood was that infection among cows was from their own species.
The scientists behind the research say if similar results are recorded in other areas, then a tactical rethink is required to stop the spread of the disease.
“Controlling the infections in cattle is essential, as it helps prevent the bacteria from infecting humans, improves cattle welfare and reduces the substantial costs to the livestock industry,” the authors of the report, published in the journal eLife, said.
Last year almost 45,000 cattle were slaughtered as a result of contracting TB – the largest number ever recorded and 50 per cent more than were culled back in 2005.
Efforts to eradicate bovine TB in 2017/18 cost £45m, and have cost half a billion pounds since 1996.
The researchers, from 12 British institutions, analysed the whole genetic code of TB-causing bacteria from 230 badgers in Woodchester Park, Gloucestershire, and 189 cattle on nearby farms, and investigated the years they were infected, exactly where the animals were infected, and if they could have had contact with each other.
The team said it was the first time they have been able to look directly at how the two species interact in spreading the disease to each other.
Badgers have been at the heart of a fierce debate over their role in the disease in cattle, with conservationists and farmers clashing over the use of culling of the protected wild animals to tackle the problem in livestock.
The scientists say the study is the first time they have been able to look directly at how the two species interact in spreading the disease to each other.
Prof Richard Delahay, wildlife biologist from the Animal and Plant Health Agency (APHA), said: “What the study shows in this area, both species are involved, you’ve got transmission from badgers to cattle and cattle to badgers and circulating within both of those populations.”
“Under that scenario, you would imagine you would probably have to control the infection in both species,” he said, though the paper did not address whether culling was effective.
The researchers said the process could be applied in other areas with bovine TB to help more targeted control, aiding efforts to control the disease and reduce the impacts on the badger population.
Professor Rowland Kao, from the University of Edinburgh, said: “The resolution of this information is so far above anything we’ve had before, it gives you a much better opportunity to understand what’s going on and understanding means refinement in terms of what we’re doing and whether it’s effective or not.”
Commenting on the findings, Prof Lord John Krebs, who led a key review on badgers and TB, said: “In terms of policy, the results do not tell us whether killing badgers is more effective than controlling cattle-to-cattle transmission, but the fact that more infections are transmitted within species than between species suggests that controlling transmission among cattle is a priority in the strategy for eliminating TB.”
Additional reporting by PA