09 October 2019 06:48
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. 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. 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. 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.
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. 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. 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. 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.
The odds of a badger visiting a neighbouring territory after a cull increased 20-fold, potentially increasing the risk of TB transmission to both cattle and other badgers, according to the scientists. They say the changes were witnessed as soon as culling began, meaning even badgers that were killed may have first spread the infection over wider areas while management was being implemented. Professor Rosie Woodroffe, at ZSL's Institute of Zoology, said: "As badger-to-cattle transmission is likely to occur through contamination of their shared environment, and TB bacteria can remain viable for long periods of time in the environment, the effects of increases in ranging behaviour could create a source of infection for several months – long after the individual badger has been culled. "In contrast, studies have shown that vaccination prompts no changes in badgers' ranging behaviour." The research group from ZSL's Institute of Zoology and Imperial's MRC Centre for Global Infectious Disease Analysis studied 67 badgers across 20 cattle farms in areas with and without farmer-led culling in Cornwall, collecting GPS-collar data between 2013 and 2017. Last year the Government commissioned a review of its strategy for tackling bovine tuberculosis (bTB) in livestock amid ongoing controversy about badger culling to control the disease.
The increased travel makes infected badgers more likely to spread the disease to new areas - while raising the chance that uninfected ones catch TB from coming into contact with new badgers and cattle. "This study suggests that culling might not be effective as an increase in the badger's range makes it more likely to come into contact with more cattle," said lead author Cally Ham, of Imperial College London. The study indicates that culling badgers allows the surviving animals to travel 61 per cent more distance each month, spreading the disease further (Photo: ZSL/PA Wire) Badger expert Lord John Krebs, emeritus Professor of Zoology at the University of Oxford, who was not involved in the study, said the research suggested that "The ill-thought out plan to control TB by killing badgers could backfire". Badgers are one source of bovine tuberculosis infection in cattle and the government is in the midst of a major cull in south west England to curb the disease. "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." The disease is a huge burden to farmers and costs the UK taxpayer £100m a year in compensation payouts to those whose infected cattle have had to be slaughtered. These projects seem to be expanding – last month, the government announced plans to extend the badger cull to 11 new areas, which will result in 63,000 animals being killed this autumn. Fuelled by the weevil's insides, the fungus then started to grow fruiting bodies topped by capsules that would release a multitude of tiny spores to infect new prey Frank Deschandol/Wildlife Photographer of the Year 1/15 A newborn hippo, just days old, was keeping close to its mother in the shallows of Lake Kariba, Zimbabwe, when a large bull suddenly made a beeline for them. Fuelled by the weevil's insides, the fungus then started to grow fruiting bodies topped by capsules that would release a multitude of tiny spores to infect new prey Frank Deschandol/Wildlife Photographer of the Year Scientists found that after a cull, badgers were 20 times more likely to visit a neighbouring territory, which significantly increases the chance of the disease being spread. Either way, research is increasingly showing badger culls look more like wild goose chases than a long term solution to tackling bovine TB.