Bovine TB: Summary of the first report to Ministers from the Independent Scientific Group on Cattle TB
Towards a sustainable policy to control TB in cattle
A scientific initiative
1. The Group was asked to advise Ministers on implementation of the Krebs report on bovine TB in cattle and badgers. Ministers recognised the Group’s wider role in developing a strategy for control of TB in cattle by looking at this issue holistically. We, therefore, recommend a package of measures which, taken together, will address the key questions which must be answered if the Government is to achieve a sustainable policy to control TB in cattle.
2. To achieve this, the following key scientific questions must be addressed:
- What is the quantitative contribution of badgers to TB infection in cattle and do the recommended proactive or reactive culling strategies result in a significant reduction in incidence of herd breakdowns?
- Might alternative badger control strategies, such as maintaining badger populations below a certain threshold, be used to control disease in cattle?
- Would these badger control strategies be cost effective?
- Can modifications be made to farm management practices that will reduce the transmission of M. bovis to cattle?
- Could monitoring of badger population density and/or prevalence of infection in badgers be used to predict risk of infection in local cattle populations?
These key questions lead on to other overlapping questions on the source of infection, factors influencing the risk of infection to both cattle and badgers and routes of transmission of infection to cattle.
3. We consider that the scientific rigour required to address these questions can be provided only by a randomised trial which is progressed in parallel with the wider measures that we have proposed, including an economic appraisal of the options which emerge from the study.
4. There are inevitably important challenges in mounting a trial of this type, not least the possibility of non-co-operation or interference which could distort data from the trial and extend the time needed to generate conclusive results. However, we do not believe that these problems are insuperable from a scientific standpoint.
5. The interests of animal health and welfare (both badger and cattle) and, in addition, important considerations of public health, underline the need to develop an armoury of measures to combat TB in cattle and fully warrant the proposed randomised trial. We would therefore support all efforts, by all parties which have a genuine and constructive interest in these issues and the co-existence of cattle and badgers, which will help to minimise any non-co-operation. The major exercise, planned by the Government, to explain the trial to interested parties will be crucial in this context.
6. In the Government consultation on implementation of the Krebs report, concerns were expressed by a number of people about welfare issues, particularly in relation to culling lactating females with dependent cubs underground and the possible use of snaring as a capture method. We have listened very carefully to these concerns and the recommended trial design reflects our desire to accommodate valid concerns about welfare without compromising the scientific rigour of the trial.
7. In making our recommendations on the trial, we have been conscious of the need for it to have a practical value in the context of possible future policies. The core aim of the trial is to present Ministers with a range of scientifically-based policy options which will be technically, environmentally, socially and economically acceptable. In this context, we examined the need for the three treatments recommended by Krebs (proactive culling, reactive culling and survey only) to be trialled. We conclude that all three are essential.
8. We recommend that trial areas (each of about 100km2) should be located in areas where the risk of herd breakdowns is high. They should be grouped into triplets, with each of the three areas within a triplet allocated to a different treatment. Proximity of the areas within a triplet will help to increase their similarities, in terms of terrain and badger density.
9. Triplets should be identified and enrolled into the trial on a rolling basis, taking account of the most recent breakdown data at the time each triplet is selected. We recognise the severe logistical difficulties for MAFF in ensuring all of the ten trial triplets currently envisaged are in place by the end of 1999 but we recommend that all possible steps should be taken to meet this target. This is essential to ensure quantitative results are available as quickly as possible.
10. An important component of the trial is an epidemiological survey to facilitate the analysis of a range of risk factors affecting TB incidence. These will include farm management systems and husbandry, climate, geographical features, badger density and levels of TB infection in badgers.
11. Any attempt to manage TB in cattle must take account of the possibility of other species acting as a source of infection for cattle and badgers. Data collected during the trial must therefore include information on other potential wildlife sources of the disease.
12. We need new ways of estimating prevalence of TB in badgers and badger numbers and density. Work on these should be conducted concurrently with the trial to develop techniques and to allow for these to be validated for use in the future. We recommend that the first issue should be addressed by a road traffic accident survey in selected areas with high TB incidence in cattle and neighbouring areas which currently have low levels of TB. The second issue is addressed in the MAFF research requirements document and we recommend that this, along with risk analysis, molecular epidemiology and cattle immunology and vaccine development should have a high priority.
13. Proactive culling involves the removal of a species which is potentially ecologically important. A preliminary study has been conducted of the environmental impact of this. We recommend that steps should be taken to quantify the environmental impact of badger culling so that this can be taken into account in assessing badger culling strategies as part of TB management.
14. The reliability of the conclusions to be drawn from the evaluation of the trial results will depend critically on the trial being properly conducted and carefully analysed. We therefore recommend that arrangements for the internal and external audit of field work should be put in place. An audit, external to MAFF, on data quality and completeness should also be done some months after the trial is commenced.
15. The current arrangements to obtain human isolates of M. bovis make it possible that some cases remain undiagnosed. We therefore recommend that the Government should consider a targeted study to enhance surveillance for M. bovis in humans.
July 1998
Page last modified:
12 August 2003
Page published: 5 February 2003