Badgers are ultimately responsible for roughly half of tuberculosis (TB) in cattle in areas with high TB prevalence, according to new estimates based on data from a previous badger culling trial.
However, only around six per cent of infected cattle catch TB from badgers, with onward transmission between cattle herds accounting for the remainder, the study suggests.
The findings are published in the journal PLOS Currents: Outbreaks.
The role of badgers in spreading bovine TB has been debated intensely as part of discussions about whether badgers should be culled to control the disease.
The Randomised Badger Culling Trial, which ran from 1998 to 2005, found evidence that culling could reduce TB in herds inside culled areas, while increasing TB in areas nearby.
Mathematical models based on data from the trial were previously used to calculate an estimate of the proportion of TB in cattle that could ultimately be attributed to transmission from badgers.
The new paper, by scientists at Imperial College London, provides a more detailed analysis. It estimates that badgers ultimately account for 52 per cent of cattle TB in areas where prevalence in cattle is high. There is considerable uncertainty around this estimate, but the authors say that 38 per cent is a robust minimum value for the estimate. There is no robust maximum value.
Professor Christl Donnelly, from the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial, said: "These findings confirm that badgers do play a large role in the spread of bovine TB. These figures should inform the debate, even if they don't point to a single way forward."
The mathematical model suggested that 5.7 per cent* of transmission to cattle herds is from badgers to cattle, with the rest of the contribution from badgers resulting from onward transmission between cattle herds.
*The 95% confidence interval for this estimate is 0.9% to 25%.
For more information please contact:
Sam Wong
Research Media Officer
Imperial College London
Email: sam.wong@imperial.ac.uk
Tel: +44(0)20 7594 2198
Out of hours duty press officer: +44(0)7803 886 248
Notes to editors
1. Christl A Donnelly and Pierre Nouvellet. 'The contribution of badgers to confirmed tuberculosis in cattle in high-incidence areas in England.' PLOS Currents: Outbreaks, 10 October 2013. The paper is freely accessible online: http://currents.plos.org/outbreaks/article/the-contribution-of-badger-to-cattle-tb-incidence-in-high-cattle-incidence-areas/
2. About Imperial College London
Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 14,000 students and 6,000 staff of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.
Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve global health, tackle climate change, develop sustainable sources of energy and address security challenges.
In 2007, Imperial College London and Imperial College Healthcare NHS Trust formed the UK's first Academic Health Science Centre. This unique partnership aims to improve the quality of life of patients and populations by taking new discoveries and translating them into new therapies as quickly as possible.
Website: http://www.imperial.ac.uk