DEFRA sets out science behind a badger cull
Chief veterinary officer Nigel Gibbens and chief scientific adviser Professor Ian Boyd set out the science behind the decision to include a badger cull in the government’s measures to combat bovine TB.
Why does the science show culling can reduce bovine TB?
Since Natural England issued a licence to allow the culling of badgers in west Gloucestershire to help tackle bovine TB, lots of bold statements about the science behind culling have been made.
We have read stories about the proposed badger cull, and a number of claims are made – culling increases bovine TB; vaccination is a viable alternative now and even that badgers don’t transmit TB to cattle.
So what do we know?
Bovine TB is a disease that is mainly seen in England in badgers and cattle, although it can also infect other mammals, including deer, goats, pigs, alpacas and humans. Its occurrence in cattle has increased progressively since the early 1980s.
We know cattle movement restrictions, slaughtering infected cattle and minimising contact with badgers won’t stop the spread of bovine TB in cattle on their own. Badger culling alone won’t halt the spread of bovine TB. Neither badger nor cattle vaccines will provide a single solution either – and currently there is no vaccine available for cattle. We need to use all the options available to us that address all the routes of transmission of the disease.
Contrary to what is being claimed in some media reports, there isn’t a cattle vaccine that is ready to be used.
The Randomised Badger Culling Trial (RBCT) demonstrated conclusively that cattle and badgers transmit the disease to one another. It also showed culling badgers leads to a reduction of the disease in cattle if it covers a large enough area, is co-ordinated and carried out under specific conditions over a prolonged period of time. Leading scientists have reviewed the results of this trial and come to the same conclusion. In addition, other countries with bovine TB, such as Australia, have found that they could not successfully eradicate the disease in cattle until it was dealt with in the wildlife which act as a reservoir for the disease.
The RBCT also indicated that remaining badgers may roam more widely after culling takes place and this could cause spread of the disease to cattle in neighbouring areas. This is known as the “perturbation effect”.
However, follow-up studies to the RBCT showed the negative effects of this perturbation disappeared 12 to 18 months after culling stopped, and the effects of the cull on reducing TB incidence in cattle lasted at least six years after culling stopped. It has been estimated that culling for five years over a 150sq km area could result in a 16% reduction in TB incidence in the local area over nine years, relative to a similar unculled area.
It is this evidence that has led to the criteria to be used in the impending pilot culls. Culling must take place over a large enough area to ensure the benefits of culling outweigh any negative effects that might be observed due to perturbation. Applicants must have considered and deployed appropriate use of “hard” boundaries and buffers such as rivers and motorways to reduce spreading the disease through badger movement, so it is possible that the cull will be more effective at reducing TB than predicted.
Vaccination
Vaccination remains a goal. The government has already funded, developed and licensed an injectable badger vaccine. But it has limitations. It is expensive to use, as badgers must be trapped before they can be vaccinated; vaccination must take place every year for a number of years, at least until infected animals die naturally; the vaccine is not 100% effective in preventing TB in badgers; and it has no benefit in already infected animals, so they will continue to spread the disease.
We are planning to invest at least £15.5m in vaccine development over the next four years and are working on both an oral vaccine for badgers, which should be cheaper and easier to use than the injectable vaccine, and a cattle vaccine. But these are both a number of years away and we can’t say with certainty when licensed products will be available.
Contrary to what is being claimed in some media reports, there isn’t a cattle vaccine that is ready to be used. We’re working hard to develop a licensable and effective cattle vaccine and a test to differentiate infected animals from vaccinated ones, as BCG interferes with the skin test. However, there are still significant licensing and regulatory obstacles to overcome before the EU will permit vaccination of cattle.
So, we know that badger culling can help reduce bovine TB in cattle, but it has to be carried out in conjunction with wider measures if we want to control and eradicate this disease. The two pilots cover a small part of England, but will verify whether culling using controlled shooting can be applied effectively, humanely and safely as part of the overall bovine TB eradication programme.
Keep up with the latest on the proposed badger cull