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Analysing the Randomised Badger Culling Trial Data from a National Cattle Perspective - SE3243

The epidemic of bovine tuberculosis (BTB) in British cattle is a growing problem with substantial economic costs to farmers and the government. It is both a problem of animal health and a zoonosis with occasional serious health consequences. While there has been considerable time, effort and expense devoted to understanding the causes of its spread and its control, thus far a coherent, integrative study that uses the considerable datasets characterising the genetic population structure of Mycobacterium bovis (the aetiological agent of BTB) and the demographics of British cattle to describe the epidemic on a national scale and evaluate control policies in this context has not yet been undertaken.

The Randomised Badger Culling Trial (RBCT) confirmed the role of badgers in the maintenance of BTB in GB, and provided evidence that cattle-to-badger transmission is potentially an important part of the epidemiological picture. Further, it was recommended that the benefits of badger culling were largely offset by an increase in incidence outside removal areas, unless those removal areas were impracticably large. However, the Chief Scientist’s report on the RBCT re-opened the case for badger culling, making the assessment of alternative control strategies of vital importance. Interpretation of the RBCT on a national scale will require more inference about how BTB transmission might vary with badger densities and cattle demographics across GB, a problem exacerbated by the substantial increase in the last decade of the geographical areas where cattle herds are tested annually for BTB, and therefore deemed as being at high risk (HRAs). In contrast to the RBCT, the Offaly study in the Republic of Ireland has shown that under their conditions, widespread culling of badgers was an effective strategy. While interpretation of these results in the GB epidemiological, social and legal context should be undertaken with caution, they emphasise that identifying the most viable British control strategy requires a more precise understanding of whether or not currently defined HRAs are likely to become more widespread, where these areas are likely to be, and whether a single approach to control is appropriate across all GB.

In this proposal we shall use RBCT data on the relationship between badger and cattle BTB both in the presence and absence of culling in combination with the populations genetics data derived from all BTB breakdowns throughout GB, and the detailed recording of individual cattle movements in the cattle tracing system. M. bovis genotypes derived from cattle show a remarkable level of spatial clustering; with patterns that appears to have been stable for at least the past decade. Using a combination of simple mathematical models of within-herd and spatial-spreading epidemics and tools from social network analysis, we shall analyse how these patterns are maintained. This project will therefore provide insights into how HRAs themselves spread, thereby better informing control of BTB with the aim of preventing this spread, and providing additional insight into the extent to which the recommendations from the RBCT are dependent on the locations chosen for the RBCT triplets.
1. Determine the best fit and likely credible ranges for herd BTB prevalence, consistent with recorded breakdown rates .
2. Determine the overlap in at the population (herd-to-herd) level between core regions for M. bovis genotypes.
3. Develop simple cellular automata models of genotype mixing at the herd level.
4. Determine whether inclusion of badger density and genotype distribution data in GB result in a statistically significant improvements in fit for models of BTB spread due to cattle movements.
5. Identify the extent to which breakdowns in the RBCT may be influenced by events at the national geographical scale.
6. Identify better ways of predicting rate of High Risk Area (HRA) spread.
7. Identify appropriate control strategies for new HRA’s, including new boundaries to established regions and isolated HRA’s.
Project Documents
• EVID4 - Final project report : SE3243 sid5   (4098k)
Time-Scale and Cost
From: 2008

To: 2011

Cost: £112,023
Contractor / Funded Organisations
University - Glasgow
Animal Diseases              
Animal Health              
Bovine Tuberculosis              
Plants and Animals              
Fields of Study
Animal Health