Research suggests culling badger not effective to stop spread of bovine TB

Wednesday 02 July 2014 20.31
An anti-cull protester outside the British houses of parliament in London
An anti-cull protester outside the British houses of parliament in London

New research has suggested that culling badgers is not an effective way of reducing tuberculosis in cattle.

A study which models the way in which TB spreads across Britain using data on cattle dating back to the 1990s found that few options could reverse annual increases in the disease.

The research, published in the journal Nature, found that only culling the whole herd when infection was found, vaccination of cattle, or additional national testing for infection would be effective in stemming the rise of the disease.

However, researchers said whole-herd culling would initially involve a 20-fold increase in the number of cattle slaughtered and the measure was a "draconian" one, which they did not advocate.

The latest analysis was seized on by anti-cull campaigners as further evidence that culling badgers to control TB in cattle did not work, but the British government rejected the findings, saying badger culling was necessary as part of measures to prevent the disease.

The model looked at transmission of bovine TB within farms, between nearby farms, and between more distant farms due to cattle movement. It also modelled the effects of control strategies on the potential spread of TB.

It assessed whether new TB cases, or breakdowns, in herds were caused by movement of cattle between farms, infection being missed during testing as the test is only around 70% effective, or by infection from the farm environment, and found 40% of new cases were due to a combination of all three.

The study was unable to separate out transmission from badgers and from other routes in the environment such as pasture where the disease lingered.

However the farm environment seemed to play a "relatively minor role" in onward transmission of TB, Professor Matt Keeling, of the University of Warwick and one of the study's authors, said.

"Only 15% of breakdowns are solely due to the environment and although the majority do feature the environment in there somewhere, if you get rid of all the environmental transmissions you'd only expect to stop around 15% of new breakdowns," he said.

Cutting environmental transmission between farms by half, which could represent the impact of a large scale badger cull, has "relatively little effect", the researchers found, and predicted that controlling badger populations would have a limited effect on TB.

Halving environmental transmission could cut the rise in TB from 10% annually to 6%, they suggested.

Prof Keeling said: "If we reduce transmission from the environment to other farms by a factor of about 50% this has a limited impact on what we see in the future, it would slow the increase in cases but not completely eliminate it."

The research found that culling the entire herd if an animal tests positive had by far the greatest effect, reducing infected cattle, numbers slaughtered and affected farms by 80% compared to standard measures after six years.

But it also had a huge cost, requiring the slaughter of 20 times the number of cattle than would otherwise be killed as part of TB control measures, although in the long run fewer animals would be slaughtered.

Vaccination had a marked effect in reducing the disease, although the vaccine offers cattle only limited protection.

Increased testing leads initially to more cattle slaughtered and farms placed under restrictions for being infected, but does reduce the disease in later years.

Prof Keeling said: "Transmission is complicated, it's multifaceted. This means you've got cattle to cattle transmission, you've got movement of infected animals and you've got infection from the environment and all of these play a role.

"This means there's no easy strategy that's ever going to rapidly eradicate infection, and what we've predicted is without substantial changes in policy we're probably going to see this historical 10% rise in cases year on year to continue.

"And we only really found three strategies that stop this rise, and that's either improved or additional testing, vaccination of cattle that slows disease progression and culling all animals on a farm which obviously is a quite draconian measure."

He and fellow researcher Dr Ellen Brooks-Pollock were not criticising existing control measures, did not advocate any one policy and that whole-herd culling was never put forward as a viable policy, they said.

The model presented a "dispassionate analysis" of the information available, the researchers said.

British farming minister George Eustice said: "We cannot accept the paper's findings because it does not investigate the full range of ways in which TB could spread. What this paper proposes would finish off the cattle and dairy industry in this country.

"TB is devastating for our dairy and cattle farmers and, along with blanket testing and removal of infected cattle, biosecurity measures, vaccination and cattle movement controls, culls will help get this disease under control."

The British environment department's chief scientific adviser, Professor Ian Boyd, said:  "Based on our current understanding of the disease cycle, the more severe control measures suggested by the paper would probably result in a rapid decline in the cattle industry in areas where TB occurs.

"However, the study reinforces the basis of the current TB control strategy which is designed to cope with complex and diverse routes of infection."

The British government introduced a TB control strategy which includes more cattle movement controls, testing, development of vaccinations for cattle and badgers, and two pilot badger culls in Somerset and Gloucestershire.

But Dominic Dyer, of the Badger Trust and Care for the Wild, said: "The government and the farming industry have focused far too much on badgers and nowhere near enough on the gaping holes in cattle management policy, which have been letting this disease through.

"This research confirms that the vast majority of new bTB outbreaks are due to poor TB testing, biosecurity and cattle control movements, so maybe farmers will now be convinced to give badgers a break and start focusing on methods that will actually work."