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ARCHIVE: Report by the Independent Scientific Review Group on TB in cattle and badgers

A report by the Independent Scientific Review Group on TB in Cattle and Badgers, chaired by Professor John Krebs, was published on 16 December 1997. This is an executive summary of the report.

Executive summary

Bovine tuberculosis (TB) is caused by the bacterium Mycobacterium bovis (M. bovis). It is currently a relatively uncommon disease in Great Britain as a whole, with new confirmed cases occurring in about 0.4% of cattle herds each year. However, the disease is becoming more common, especially in South-West England, its traditional stronghold, where new cases occur in more than 1% of herds each year, in some parts of Wales and in the West Midlands. The control of TB in cattle is a complex problem and there is no single solution. We recommend a combination of approaches on different timescales.

For affected farmers, bovine TB imposes very significant economic and welfare consequences, and for the animals involved there is also an important welfare cost. Furthermore, on behalf of the taxpayer MAFF currently spends about 16 million per year on control and related issues, including tuberculin testing carried out according to an EU directive. If the disease were to become more common, these costs would increase and there could be significant trade implications.

Human TB is primarily caused by Mycobacterium tuberculosis, although M. bovis can be involved. Currently, as a result of pasteurisation of milk and tuberculin testing of cattle, there is a negligible risk to the human population of Great Britain from M. bovis (32 confirmed cases in the UK in 1995); but the disease has the potentialto be a significant health risk.

Cattle in other countries in Europe and elsewhere also have infections of M. bovis, notably New Zealand, the Republic of Ireland, Italy and Spain.

The sum of evidence strongly supports the view that, in Britain, badgers are a significant source of infection in cattle. Most of this evidence is indirect, consisting of correlations rather than demonstrations of cause and effect; but in total the available evidence, including the effects of completely removing badgers from certain areas, is compelling.

It is not, however, possible to state quantitatively what contribution badgers make to cattle infection, because the relevant data have not been collected and analysed. Collection of the relevant data, statistical analysis and the use of modern molecular techniques could resolve this question and we recommend that these should be high priorities for MAFF. Other wildlife species also carry the disease, and the possibility of some contribution from these species cannot be ignored.

Recognising the importance of badgers as a source of infection, over the past two decades, MAFF has implemented, in succession, a variety of policies for killing badgers in order to control the disease in cattle. However, it is not possible to compare the effectiveness of these different policies; nor is it possible to compare any of them with the impact of not killing badgers at all, because there have been no proper experiments.

However, the indication is that more severe culling policies involving complete, or near complete, removal of badgers from an area, are more effective at reducing the herd breakdown rate than is less complete removal. An attempt to target the control at infected badgers only (the ‘live test trial’) was unsuccessful because of the low sensitivity of the test for TB in badgers.

We recommend that MAFF should set up an experiment to quantify the impact of culling badgers. The experiment, in which farmers should play a role, should involve three treatments: proactive culling of badgers, reactive culling following the identification of TB in cattle and no culling. Both of the culling policies should include lactating sows.

The experiment should be overseen and analysed by an independent Expert Group. The experiment will enable MAFF to carry out a cost-benefit analysis of killing badgers to control TB in cattle. The cumulative number of badgers killed in the five years of the experiment is unlikely to be substantially different from the number killed in the present interim policy (roughly 2,000 a year on the basis of 1996 figures). Moreover, it is likely to be significantly less than the number killed in road traffic accidents.

Detailed analysis of the spatial distribution of TB in cattle during the period 1987 to 1996 shows that in some places past history of infection is a good predictor of future risk: repeated infections and infections on neighbouring farms are principally restricted to a small number of areas in Great Britain. It is in these areas of repeated occurrence of TB that the impact of treatments involving culling badgers would be greatest and most quickly seen.

We therefore recommend that the experiment outlined above is carried out in a minimum of 30 10km by 10km highest risk areas (‘hot-spots’). The precise areas to be included should be finally determined by the Expert Group. Equal numbers of hot-spots should be assigned at random to each of the three treatments.

For the remainder of the country, we recommend that no culling is carried out. Outside the hot-spot areas, the risk of repeat infection or of neighbouring farm infection is relatively low and therefore the potential benefits of culling badgers are also low. The Expert Group should, however, keep the situation under review and retain the option to recommend recruitment of additional areas into the experiment if appropriate.

Although the route of transmission from badgers to cattle is not known, simple husbandry methods to separate badgers and cattle could have a significant role in reducing risk. The current MAFF guidelines are apparently not widely heeded by the farming industry, nor has there been any attempt to ascertain the impact of husbandry on risk.

We recommend that outside the hot-spot areas the farming industry itself should take the lead in carrying out a proper experimental comparison of the impact of a small number of simple husbandry techniques. MAFF’s role should be to provide advice/analysis on experimental design and results and to provide incentives to the industry to participate and subsequently to adopt best practice. Husbandry may well play an important role as part of the long-term solution.

In the long run, the best prospect for control of bovine TB is to develop a vaccine for cattle. This is a long-term (more than ten years) strategy and success cannot be guaranteed. However, targets and milestones can be identified to monitor and evaluate progress at five yearly intervals. We recommend that the development of a cattle vaccine and an associated diagnostic test to distinguish infected from vaccinated cattle should be a high priority for MAFF’s long-term research strategy.

A badger vaccine, although posing greater technical problems in terms of both development and delivery, should also be kept as an option. During the next five years much of the basic research required will be relevant to both badgers and cattle.

Proper co-ordination of the research will be essential. In developing its research strategy MAFF should take into account work on human TB including genome sequencing, and work on animal vaccines and diagnostics in other countries. Industrial involvement should also be explored.

We recommend that MAFF’s future strategy for research on, and control of, bovine TB should take account of the following points:

(i) MAFF should ensure that it commissions research from the best groups in the research community;

(ii) there should be a better co-ordination of modelling and data collection to ensure that the appropriate data are collected and that best use is made of them in analyses;

(iii) data should be freely available to facilitate the best analysis and to engage the wider research community;

(iv) there should be better co-ordination of MAFF-sponsored research on TB and the work of other public funders (e.g. Research Councils) and industry; and

(v) the total amount spent on TB research (1.7 million) as well as the relative amount (nine times more is spent on control than on research) should be reviewed in the light of the costs of TB control and the potential returns from research. The industry could contribute to the costs of control as they do in New Zealand, where the absolute amount spent on research by the Government is three times higher than in Britain and the amount of Government money spent on control is just under twice that spent on research.

 

 

Page last modified: 19 December 2005
Page published: 5 February 2003