Badger culls fail to halt spread of cattle tuberculosis, study shows

Widespread culls of infected herds has only short-term success, survey by Imperial College and Zoological Society of London finds
Ian Sample, The Guardian 10 Feb 10;

Badger culling is unlikely to halt the spread of tuberculosis in British cattle herds, according to a survey of disease in regions where culls were trialled.

Widespread and repeated culls reduced the numbers of infected cattle, but the disease returned to its original level four years after the programme ended, scientists found. Managing badger populations to stop them spreading TB to cattle cost more than the impact of the disease, researchers from Imperial College and the Zoological Society of London said.

Farmers have urged the government to permit a large-scale cull to deal with the effects of the cattle TB, but in England the measure has been ruled out. The Welsh assembly is poised to go ahead with a cull to tackle the disease in one of its hotspot areas. Professor Christl Donnelly, of Imperial College London, said that if a cull were to be undertaken, it would have to be widespread and repeated.

Donnelly led a team that checked for TB in cattle in and around 100 sq km areas where badger culling was trialled. Badgers were culled proactively at 10 sites and "reactively" at 10 others sites, where culling took place only when cattle fell ill with the disease. Badgers were not culled in a further 10 regions.

In areas where culling was repeated annually, cases of TB fell 23.2%, but in the area immediately surrounding the cull zone, disease rates rose by 24.5%. The rise was due to surviving badgers ranging farther as their territories expanded.

There was a net benefit of culling only if the area was sufficiently large for the fall in disease inside the cull zone to outweigh a rise around the edges.

After culling ceased, the number of infected herds in the areas was reduced by 42% between one and three-and-a-half years after the final cull, although the benefits had disappeared after four years.

A sustained five-year cull in an area of 150 sq km would prevent the infection of 22.6 herds, the study found, saving about £610,000. But a widespread cull over 150 sq km using trapping, snaring or gassing would cost between £1.35m and £2.14m, outstripping the savings, the researchers calculated. The study is published in the journal Plos One.

"If you are going to undertake culling, it should be widespread, co-ordinated and repeated," Donnelly said, adding that the Welsh assembly should "seriously consider" the prospect of a badger vaccine, which is being deployed in half a dozen TB hotspots in England this year.

Dr Christianne Glossop, the chief veterinary officer for Wales, said: "What we are proposing is to combine a limited cull of badgers with strict cattle control measures within a defined area over a sustained period. Although there are similarities between the [trial] and the pilot area, the differences are so significant to prevent true comparison of the results and we are confident of a much longer-term success rate as a result. In the last 10 years we have spent almost £100,000,000 on compensation alone in Wales. We can't let this situation continue unchecked."

Benefits of badger culling not long lasting for reducing cattle TB, says study
EurekAlert 10 Feb 10;

Badger culling is unlikely to be a cost-effective way of helping control cattle TB in Britain, according to research published today in PLoS ONE.

Badger culling is unlikely to be a cost-effective way of helping control cattle TB in Britain, according to research published today in PLoS ONE. The authors of the study, from Imperial College London and the Zoological Society of London, say their findings suggest that the benefits of repeated widespread badger culling, in terms of reducing the incidence of cattle TB, disappear within four years after the culling has ended.

Bovine tuberculosis (bTB) is a disease in cattle that has a serious financial impact on farmers in Britain, as infected animals have to be slaughtered. In 2008, 2,738 herds were infected with bTB, costing the government over £100 million. Wild badgers can become infected with bTB and are known to transmit the infection to cattle. Because of this, UK governments have tested various means of badger culling to control bTB infection in cattle over the past 30 years.

The Secretary of State for Environment decided against badger culling to control cattle TB in England in 2008. However, the Welsh Assembly Government now proposes to implement a badger cull using methods very similar to those used in the culling trial, though it faces a legal challenge to this proposal.

The researchers behind the new study analysed data from the Randomised Badger Culling Trial (RBCT), a large-scale field trial that was undertaken in 1998 by Defra to assess the effectiveness of badger culling. The results showed that although the incidence of cattle bTB reduced during culling and in the first years after the final cull, these reductions subsequently declined. The benefits were undetectable within four years after the final cull.

Professor Christl Donnelly, senior author of the study from the MRC Centre for Outbreak Analysis and Modelling at Imperial College London, said: "Bovine TB is a big problem in Britain and the disease can profoundly affect farmers' livelihoods. We know that bTB is transmitted between cattle and badgers, so the Randomised Badger Culling Trial was set up to find out if culling badgers would help control the spread of the disease. There has been some controversy over badger culling as a bTB control method and it has been unpopular with the general public.

"Although badger culling reduced cattle bTB during the trial and immediately thereafter, our new study shows that the beneficial effects are not sustained, disappearing four years post-cull. Our new research also suggests that the savings that farmers and the government would make by reducing bTB infections in cattle are two or three times less than the cost of repeated badger culls as undertaken in the trial, so this is not a cost-effective contribution to preventing bTB infections in cattle," added Professor Donnelly.

In the RBCT, ten areas of 100 square kilometres were subjected to badger culling, and compared to ten similar areas with no culling. Culls were repeated annually and ended in October 2005. Previous analyses have shown that during the cull, bTB incidence in cattle within the cull zones decreased, whereas disease incidence in cattle outside cull zones increased, offsetting the benefit.

Today's study shows that after the culling finished, the number of infected herds inside cull areas was on average 37.6% lower than the number of infected herds in non-cull areas. The results also show that this benefit diminished over time after the culling ended, by 14.3% every six months. By months 43-48 after the final cull, there was no remaining beneficial effect. The research also shows that since the culling finished, the number of infected herds in two kilometre zones outside cull areas was comparable to the number of infected herds in areas outside non-cull areas.

The researchers also analysed the financial costs and benefits of badger culling. Over the seven and a half years during which five annual culls would have detectable benefits on the incidence of cattle bTB, culling in an area of 150 square kilometres would be expected to prevent the infection of 22.6 herds of cattle. The average cost of an infected herd has been estimated to be £27,000, meaning badger culling would save £610,200. However, the cost of a badger cull over a 150 square kilometre area would be between £1.35 million and £2.14 million, using cage trapping, snaring or gassing.