Badger Culls Risk Increased Spread Of TB To Cattle, Study Finds

Culling badgers drives them to roam further afield, allowing them to disperse tuberculosis over a larger area, new research suggests.

The culls might thus increase the risk of TB spreading to cattle, the scientists behind the study warn.

The government commissioned its own review of the culls, but has yet to respond to the recommendations.

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The review urged the government to explore alternative approaches to culling.

It was led by zoologist Sir Charles Godfray, from Oxford University.

The government said its own research indicated that the culls were working.

Co-author Rosie Woodroffe, from the Zoological Society of London (ZSL), said the results backed the scientific consensus that culling will – at best – slow the spread of TB only to a modest extent.

Additionally, it could potentially accelerate infection.

“There is an expectation from some farmers that the cull will be a silver bullet and it will make everything much better. But these results explain why those expectations are so misplaced,” Prof Woodroffe told BBC News.

“Culling is a very imperfect way of controlling the spread of TB from badgers to cattle.”

Dominic Dyer, chief executive of the Badger Trust, said the authorisation of culling licences in 11 new areas was taken before the government had responded to its own review of badger policy. This was “a national disgrace”, he said.

Mr Dyer added: “Badger vaccination removes the risk of perturbation and brings farmers and wildlife protection groups together in a spirit of mutual respect, trust and confidence.

“The focus should then be moved to improving TB testing systems, bio security measures and cattle control movements, as recommended in the Sir Charles Godfray TB Policy Review.”

A spokesperson for the Department for Environment, Food and Rural Affairs (Defra) said it would respond to Prof Godfray’s review in the “near future”.

Prof Woodroffe was among a group of researchers who explored the effectiveness of culling in extensive trials lasting nine years from 1998 to 2006. The Krebs Trial found that culling did control TB to some extent in the cull areas, but found that it temporarily increased cattle TB in surrounding zones.

The assumption was that although the culls reduced the number of infected badgers, the ones left were more effective in spreading infection because they moved around more. The new study, published in the Journal of Applied Ecology, confirms that assumption.

Co-author Cally Ham, from ZSL, tracked the movement of 67 badgers with GPS collars across 20 cattle farms in Cornwall, in areas with and without culling.

She found the badgers in culling areas covered an area of land 61% larger than badgers in zones without culling. They also visited 45% more fields. The odds of a badger visiting the territories of other badgers each night increased 20-fold. The increased movement began as soon as culling began.

These observations are significant because badger to cattle transmission of TB is thought to be principally from bacteria left in fields by infected badgers. The increased movement caused by culling could, therefore, create a source of infection for several months, long after individual badgers have been culled.

“This potentially increases the risk of TB transmission both to cattle and to other badgers,” said Ms Ham.

The culls were instigated in 2012 because of hardship to farmers and the growing cost of the disease to the UK economy, which currently stands at £500m over the past 10 years. This is projected to increase to £1bn in the next 10 years, according to the National Farmers Union (NFU).

Vaccination might be a more effective solution to culls

Vaccination might be a more effective solution to culls

The NFU’s vice president, Stuart Roberts, said he believed culling was reducing the incidence of cattle TB.

“We are still awaiting the peer-reviewed report examining the effectiveness of the cull at reducing TB,” he said.

But he added: “Previously published peer-reviewed research, and anecdotal evidence from farmers in these areas, indicates strongly that TB is being reduced as a result of controlling the wildlife which carry and spread the disease. We do not see similar convincing outcomes from vaccination.”

A Defra spokesperson said the department’s cattle TB control policy already takes into account a potential increase in badger movement by ensuring there is an intensive cull across an area.

“Research shows culls in higher risk areas have had a positive impact on [bovine TB] incidence in cattle, which is the key measurement by which the effectiveness TB prevention can be tested,” they said.

“There is no single measure that will provide an easy answer to beating the disease and we are pursuing a range of interventions to eradicate it by 2038, including tighter cattle movement controls, regular testing and vaccinations.”

 

(Source – BBC News – Science & Environment – Pallab Ghosh, Science correspondent, BBC News – 09/10/2019)

Bovine TB Strategy Review – Godfray et al – Oct. 2018

Read the report online at: https://www.gov.uk/government/publications/a-strategy-for-achieving-bovine-tuberculosis-free-status-for-england-2018-review

 

Badger culling has ‘modest’ effect in cutting cattle TB

An independent scientific review has said that badger culling can have a “modest” effect in reducing cattle TB.

But it adds that the policy would lead to more than 40,000 badgers being culled a year.

Badgers move in as soon as culling begins and so spread infection further. - Pic. Seth Jackson

Badgers move in as soon as culling begins and so spread infection further. – Pic. Seth Jackson

The report says that such high levels of culling may not be publicly acceptable.

The authors urge the government to accelerate the development of non-lethal controls, such as vaccination.

The findings were published in a review led by Prof Sir Charles Godfray of Oxford University.

But one expert said the report had little to say about the effectiveness of the current badger culls.

The report was commissioned by Michael Gove, Secretary of State for Environment, Food and Rural Affairs, in February.

He asked an independent group of scientists to review Defra’s strategy for controlling the spread of tuberculosis (TB) in cattle. According to Prof Godfray he was “explicitly asked” not to look at the effectiveness of the current culls.

Instead Prof Godfray and his team drew on the results of the Randomised Badger Control Trials carried out between 1998 and 2007.

Natural Boundaries

These showed that culling tended to increase TB in badgers because of increased movement.

It did, however, find that a reduction of between 12% and 16% in the rate of new cases of cattle TB was theoretically possible, but with significant caveats: the culling had to be carried out over a large area with natural boundaries for between eight to twelve days each year for four years and that more than 70% of badgers had to be killed.

Since culling began in 2013, scientists and campaigners have expressed concerns that the culls that have been rolled out by Defra have not been in accordance with the strict criteria set out by the expert group because they have proved too expensive or too difficult.

They say that improperly conducted trials could actually increase cattle TB rates.

But Prof Godfray notes that, in principle, culling is one of the tools ministers have at their disposal and it should be up to them whether its marginal benefit was worthwhile.

“We conclude that culling does have an effect on the disease. The phrase we use is ‘a real but modest effect’,” he said.

“If nothing else is involved then one would obviously cull, because if one does not cull one is throwing away one of the tools. But of course there are many other factors involved.”

Another argument Prof Godfray puts forward in favour of culling is that it makes affected farmers more amenable to carry out unpopular and costly disease control measures on their farms and in transporting their cattle.

“It is likely that the farming industry would be more willing to accept other interventions that could negatively affect dairy and beef profitability if they believed that the threat of transmission from badgers was being robustly addressed,” he said.

The report warns however that continued culling “would not be acceptable to some (possibly large) sections of the public, and the costs of policing could be substantial” and says that a shift away from culling is “highly desirable”.

Specifically, it emphasises the need for a proper evaluation of badger vaccination.

Testing Regime

Prof Godfray’s report also states that infections from cattle to cattle is higher than had been thought, possibly because the current so called skin test used to test for the disease is less reliable than experts once believed. It therefore urges that Defra adopts more sensitive tests.

Culling badgers has a 'modest' effect in slowing the spread of TB say experts

Culling badgers has a ‘modest’ effect in slowing the spread of TB say experts

The farming minister welcomed the report and said that Defra would give its response by next summer.

”We welcome this review of the government’s 25-year Bovine TB strategy and I extend my thanks to Sir Charles Godfray and his team for their hard work in producing the report.

“Sir Charles’ report is an important contribution that will inform next steps in the strategy to achieve officially TB free status for England by 2038.”

Prof Rosie Woodroffe of the Zoological Society of London (ZSL) said that the report had many good ideas but said nothing about the effectiveness of the current badger culls.

“The report contains little critical evaluation of whether the current farmer-led culls are effectively reducing cattle TB,” she said.

“It reports results from the first two years of monitoring without mentioning any of the caveats included by the original authors. It makes no mention of more recent data, which have suggested incidence might be falling in two areas but rising in a third.”

Prof Lord John Krebs from Oxford University, who led the Randomised Badger Control Trials, said that the report indicated that Defra and farmers need to do more if cattle TB is to be stamped out.

“Currently, much of the spread of TB in cattle arises from a combination of disappointingly low uptake of measures to prevent cattle coming into contact with badgers, trading of infected cattle, and the low sensitivity of the standard skin test for TB, which means that there is likely to be a hidden reservoir of infection in many cattle herds in high risk areas,” he said.

“Unless the government and the farming industry tackle these problems now, TB will not be eradicated or controlled.”

(Source – BBC News – Science & Environment –  Pallab Ghosh, Science correspondent, BBC News – 13/11/ 2018)

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