Scottish Government

Preparing for a new GB strategy on bovine tuberculosis

4. A new approach

4.1 What are the challenges?

4.1.1 In GB bovine TB has been increasing at a rate of 18 per cent per annum for new herd incidents and at 20 per cent per annum for reactors culled. Despite current control measures, we have no reason to suppose that this will change significantly in the next say 5 - 10 years without major changes in policy. As a result the costs to the beef production and dairy industries will continue to increase as businesses are disrupted and movement restictions are enforced. Additionally UK Government expenditure may double every 4 years leading to a total expenditure of over £1 billion over the next 8 years.

4.1.2 Figure 2 shows a forecast of public expenditure based on pre FMD trends. It does not take account of any possible biological factors that might limit the rate of increase of the disease over time. It includes compensation and related costs in GB plus non-compensation related costs (comprising testing and laboratory costs, State Veterinary Service (SVS), research and administrative cost). In making this forecast, we have assumed that these costs will rise by 20 per cent annually (except for research where an assumption has been made that costs will remain fixed and administration where a 2.5 per cent annual rise in costs has been assumed).

Figure 2 The forecast public expenditure on bovine TB in GB under current TB policies

4.1.3 The key challenge is for Government, in partnership with industry and others, to reduce the incidence of TB in the national herd which will reduce the overall economic impact of TB (disease and controls). New compensation arrangements need to be put in place to rationalise compensation across animal diseases leading to simplified and more transparent compensation procedures by the end of 2004. Establishing more effective co-operation between the SVS/Local Veterinary Inspectors (LVIs) and farmers and improving SVS procedures will also contribute.

4.1.4 Critical to reducing the economic impact of the disease is identification and introduction of effective disease control mechanisms that can contain, control and diminish the level of infection in the GB herd in a cost-effective manner.

4.1.5 The core of our problem is that evidence from other countries shows that, in the apparent absence of a significant wildlife reservoir, cattle controls based on regular testing (using skin test), culling, slaughterhouse checks and movement restrictions including tracing and contiguous testing can be effective at controlling the disease. Many EU countries, but not the UK, are Officially Tuberculosis Free. This does not imply that infection is eradicated from livestock or wildlife, merely that incidents are at or below the thresholds in the EU Directive.

4.1.6 In GB, our current cattle controls are not proving to be effective in controlling the disease. Nevertheless, we do not underestimate the effectiveness of the control measures in place in detecting and removing infected animals - the consequences of suspension of TB testing during most of 2001 illustrates the potential for the disease to spread in cattle in the absence of routine testing/controls. The number of animals slaughtered in 2000 was 8,000 compared with the post-FMD situation in 2002 when 23,000 cattle were slaughtered. In Scotland in 2000 only 40 animals were slaughtered but the figure rose to 191 in 2002. Thus , we must look critically at strengthening cattle controls including on-farm measures and consider what additional contribution wildlife control measures might make.

4.1.7 Withdrawing from current cattle controls is not an option. There are requirements in EU legislation, and there are areas of GB with low incidence of TB that we want to keep this way. Proposals in part two of this consultation recognise need to take action on cattle to seek to prevent spread of the disease in cattle from high risk to low risk areas of GB.

4.2 Towards a new TB Strategy

4.2.1 This consultation invites views on the overall approach that we should take in pursuing the Animal Health and Welfare Strategy and developing a new TB strategy. These views will be taken into account in working up detailed policy options for further consultation in 2004.

4.2.2 Our starting point is that a new bovine TB strategy must:

• define a vision of a future for TB policy that has resonance with all key players;
• review the rationale for Government intervention in seeking to control the disease and, bearing in mind the costs and benefits, seek proportionate interventions which strike the right balance on behalf of society;
• review the national and EU regulatory framework and make or press for changes if appropriate;
• be based on the best scientific evidence so must take account of existing and emerging scientific evidence and research findings; of course scientific evidence will not be the sole determinant of policy direction; there are likely to be environmental, economic, social and political issues to consider. Continued investment in a range of R&D is envisaged;
• define roles and responsibilities of the farming industry, the veterinary profession and wildlife interests in relation to bovine TB prevention and control;
• review arrangements for working in partnership with stakeholders and securing expert advice; and
• set targets and indicators so we can chart, review and evaluate progress.

4.3 Establishing a vision for bovine TB

4.3.1 The Scottish Executive is working with the industry and consumers to secure a sustainable future for our farming and food industries, as viable industries contributing to a better environment and health and prosperous communities. The Animal Health and Welfare Strategy derives from this and sets a vision for the future. With that as our basis we need to arrive at a robust, fair and cost-effective settlement on bovine TB that sets out where Government and stakeholders hope to be in 10 years time and reconciles the contending perspectives of stakeholder groups. Achieving everybody's aspirations is unlikely. We will also need to develop challenging but realistic targets and indicators of success which recognise the regional distribution of the disease and scientific uncertainty around the effectiveness of TB control tools.

4.3.2 As well as setting out what we hope to achieve in terms of disease control, the vision will also set out what we can all expect from all key groups. We need to agree the roles/responsibilities of the key players in relation to bovine TB and get their commitment to achieving the vision and targets. Our initial ideas are set out below:

• Livestock keepers - responsible for maintaining good disease prevention and control practices to reduce the risk of TB incidents in their herd and to reduce the spread of bovine TB to other herds and to wildlife;
• Veterinary profession - a core role in promoting/advising on TB prevention as well as delivering disease surveillance and control;
• Animal welfare and environmental interest groups - a key role in education and advice;
• Scientists/researchers throughout GB (including Scotland) - provide evidence base for informing policy plus tools for disease control;
• Government and its agencies, including local government - Establishes regulatory framework and delivery and enforcement regimes, major funder of research and surveillance, and promoting best practice, monitor public health issues;
• Livestock and food chain related interests: contribute to promotion of good animal health practices, including as part of quality assurance, promoting consumer awareness; and
• Consumers - should be aware of choices being made when purchasing food and implications.

4.3.3 Whilst we recognise that eradication in cattle across GB might be a popular 10 year target or 'vision', this is not within our reach in this timeframe. To achieve this would require an effective cattle or badger vaccination strategy to be applied in the field now coupled with badger control strategies and more effective cattle movement/husbandry controls. However, there are areas of GB, such as Scotland, where TB incidence in cattle is low. We must aim to prevent the spread of TB into these areas. Minimising the incidence of TB in cattle in Scotland and other low incidence regions of GB may be achievable in this timeframe if appropriate controls were put in place.

4.3.4 Achieving a sustained reduction in incidence rate in cattle in high risk areas, both in terms of absolute numbers of new TB incidents and slaughtered cattle and in relation to the numbers of herds and cattle tested is also a huge challenge, given the present position.

4.3.5 Reduction in the rate of increase in incidence in cattle is still some way from what we are achieving with current controls.

4.3.6 Control of geographic spread of TB in cattle, to ensure that those areas currently free of TB remain so, or reduction in the size of the affected area may be realistic goals and are the aims of the short - term measures proposed in part two of this document. However, without more information on what elements of local disease spread might be due to wildlife as opposed to cattle, the benefits of cattle based measures alone will be difficult to predict.

4.3.7 We will need to develop targets for reduction in the economic cost of bovine TB controls to the taxpayer and industry, at the same time increase cost-effectiveness of the delivery of control. Actions are likely to embrace implementation of a new cattle valuation and compensation regime , improve efficiency of delivery of existing TB controls, and introduce more effective disease control measures.

4.3.8 We will need to continue to monitor the number of human cases of M. bovis although the majority of human cases are not or cannot be linked to recent occupational exposure with infected cattle.

4.3.9 Questions:

) Bearing in mind we are looking at what we might achieve in terms of bovine TB controls in the next 10 years, do you agree that the most realistic target has to be to contain and progressively reduce spread, incidence and economic costs of the disease and to continue to develop the science base to inform future strategy?QUESTION 1(

) In defining what we hope to achieve in terms of bovine TB disease control, to what extent should this be regionally differentiated to reflect the distribution of the disease?QUESTION 2(

) How should the interests of wider society, and the principles of sustainability be recognised in a 10 year vision for bovine TB?QUESTION 3(

4.4 Rationale for Government intervention

4.4.1 In developing a new Strategy we need to consider the policy goals, why they may not be delivered without Government intervention, what actions might be available and if the costs are justified.

4.4.2 Broadly speaking, Government intervenes in relation to animal health and welfare for the following reasons:

• To protect human health;
• To protect interests of the wider economy and society;
• To secure opportunities for trade; and
• To protect and promote animal welfare

4.4.3 Historically, the Government has introduced policies for the control of bovine TB primarily in order to protect public health. These controls have included limiting the presence of disease in the cattle population by testing and compulsory slaughter of reactors, meat inspection in slaughterhouses and the pasteurisation of milk for human consumption. The contribution which each of these elements makes to the protection of public health is difficult to establish. In 1996, in light of these controls, the Krebs report concluded that the current risk of human health infection with M. bovis in Great Britain was negligible. It added however, that the disease had the potential to cause problems and that a rationale underlying policies for control of bovine TB was to ensure that this risk did not increase.

4.4.4 Study of the historic prevalence of M. bovis TB in humans leads us to conclude that the heat treatment of milk and meat inspection are the major contributors in consumer protection. The extent to which cattle testing and related controls contribute to public health protection is difficult to assess. It is possible that, should the controls in cattle be eased, the burden of infection, including the re-emergence of disseminated TB with lesions in the udder, would increase to such a degree that the heat treatment of milk and meat inspection were less effective in providing protection to the food chain.

4.4.5 The change to public health hazards that might be associated with contact with infected cattle or wildlife in the face of increasing incidence of bovine TB is also difficult to estimate. We currently have no evidence of increased public health risks where wildlife reservoirs of TB are established. Neither do we have evidence of the occupational health risks to farmers, other agricultural workers and the immuno-compromised if the disease is permitted to continue to spread in cattle. However, given the long incubation period of the disease in humans and the absence of active surveillance in at-risk populations, we would not expect to be aware of this for a considerable time. There is therefore a precautionary element to the current controls, since we do not know what the public health risks would be if controls were relaxed and if cattle therefore were able to reach later stages of disease.

4.4.6 Bovine TB in cattle also has serious implications for animal health and welfare. The responsibility for protecting the welfare of farmed livestock rests with the owner or keeper of the animal. However, in the case of bovine TB (like some other cattle diseases such as Enzootic Bovine Leucosis, brucellosis, and FMD) the economic consequences of outbreaks of the disease have led to international controls under the auspices of the Office International des Epizooties (OIE) and the EU. These controls regulate trade in live animals in order to protect countries which are free from the disease and provide standards under which countries not free from the disease may be permitted to continue to trade safely. In order for countries which are members of the OIE or the EU to maintain their trading status, Government intervention is required (although neither of these organisations requires that the cost of Government intervention is met from the public purse). Government intervention in the control of TB in cattle may therefore be necessary to secure opportunities for trade.

4.4.7 Bovine TB also has economic implications for individual affected farm businesses. On the one hand, the measures, which the Government has put in place to control the disease, place an economic burden on farmers. On the other hand, where there is an outbreak of disease, leaving the disease unchecked would itself produce significant costs for farmers, including lower productivity from infected animals.

4.4.8 It has been suggested that the control of bovine TB will be beneficial to the health and welfare of wildlife species, notably the badger. TB is not a major cause of death in badgers, compared to, say, road traffic accidents. There is no evidence that TB infected badgers suffer a long and painful death, although of course there might be a short period of debilitation during the terminal stages of the disease. Individual badgers can live in excess of four years while in the excretory stage of the disease and may show no signs of being ill. Indeed, in the case of females they can reproduce and rear litters successfully. The onset of progressive disease in infected animals is probably associatedwith environmental stressors, such as food shortage.

4.4.9 As a result of the Protection of Badgers Act 1992, the badger population in Great Britain is currently increasing, and it is expected to continue to do so until it reaches the natural carrying capacity of the available habitats. This natural population growth, despite the known presence of TB infection in certain areas, would support the view that bovine TB is not presenting a significant welfare challenge to badgers in the wild. Disease is a natural feature of ecosystems; indeed it can be an important population regulatory factor. Government does not normally intervene in these natural regulatory processes.

4.4.10 Question:

) Does Government need to intervene in the control bovine TB? If so, why, and to what extent? If not, why not?QUESTION 4(

4.5 Balancing costs, benefits and risks

4.5.1 If it is concluded that Government does need to intervene to control bovine TB, the question arises as to whether the taxpayer should contribute to the resulting costs and, if so, to what extent. This should reflect where the balance of responsibility lies for managing the risks, and who benefits from the controls. The new Strategy will need to examine this and seek to address inconsistencies.

4.5.2 It has been argued that, in the absence of a wildlife reservoir of infection, it would be possible to eradicate the disease from GB and that the farmer, by tolerating or having to tolerate a wildlife species which presents a threat to his livelihood, is providing a public good. If this were to be acknowledged, the cost of bovine TB to the farmer is, in effect, the cost which society at large has placed on the farmer by the protection of wildlife species which can act as a reservoir of infection. The Strategy will therefore need to ensure that the financial burden which TB and TB controls place on the farmer are fair and balanced. The randomised badger culling trial will not provide a definitive estimate of the contribution, which badgers make to the incidence of bovine TB in cattle, but it may provide some information, which will help to establish a fair division of the costs between farmers and the taxpayer.

4.5.3 Another argument for a taxpayer contribution to controlling TB is that there are public good aspects to the policy, particularly as these relate to the protection of public health.

4.5.4 Public good aspects of control of bovine TB would justify the taxpayer bearing a share of the costs. However, if the main beneficiary of the intervention is the herd owner as the health of his/her herd is protected the cost of that intervention should be borne by the herd owner. Between these two extremes is a range of options for sharing the costs of TB control.

4.5.5 Currently, the costs of the main public health protection measures in relation to bovine TB, heat treatment of milk and meat inspection, are borne by the industry in the first instance (producers and processors) except to the extent that meat inspection charges are subsidised.

4.5.6 Livestock keepers benefit from TB controls as higher health status herds are more productive and, in the longer term, provides more opportunity for trade. Livestock keepers have responsibility for managing disease risk and whilst consequential losses of TB incidents are borne by the farmer, the new strategy needs to determine if they should bear a greater share of the financial risks. The new strategy will need to examine how policies can provide appropriate incentives to livestock keepers to minimise risks on their farms. There is an argument that the farming industry should bear the costs of the damage it can do to the wider public good as with examples outside farming. For example, farms without feedstore security may inadvertently be providing food for badgers or other wildlife and exacerbating any disease risk. Farmers purchasing cattle without taking precautions to test for the presence of TB, or taking positive biosecurity measures, may also increase the risk of spreading disease.

4.5.7 At present, the taxpayer bears the cost of carrying out research into bovine TB, surveillance and control of the disease in cattle where it is identified. Costs of surveillance and control could be transferred to the industry, either by recovering costs from individual farmers (in the case of surveillance) or from the industry as a whole. Alternatively, any costs for the additional measures which are considered by farmers to be essential to bring the disease under control could be introduced at their expense, with the Government acting as a facilitator where legislation and enforcement are required to ensure the success of the measures adopted.

4.5.8 Questions:

) Who in your opinion are the main beneficiaries of current bovine TB controls and how should costs be shared between beneficiaries?QUESTION 5(

) What contribution should the farming industry make to reduce the risks to their herd of bovine TB?QUESTION 6(

4.6 Development of future policies

4.6.1 In developing future policies, it will be important for all stakeholders to accept the complex nature of this disease and recognise that, for the foreseeable future, we need to deal pragmatically with TB in cattle using current scientific evidence.

4.6.2 An unmanaged and infected badger population may be central to the dynamics of the disease and transmission to cattle. A key scientific issue for Government has been therefore to clarify the potential role of badgers and other wildlife in spread of bovine TB in cattle and, with stakeholders, devise management strategies to control transmission of the disease between badgers/other wildlife and cattle. Without tackling exogenous infection, cattle based measures may not be sufficient to have a significant impact on the incidence of the disease. One consequence of this is that individual farm businesses may face decisions about the long term viability of cattle farming if they are in areas of the country with high persistent incidence of TB.

4.6.3 Any badger/wildlife management strategies, whether culling or vaccination, would need to be deployed in conjunction with cattle based controls which may be informed and strengthened by results of research on cattle pathogenesis, epidemiology, development of improved diagnostic tests (including gamma interferon) and, in the longer term, vaccines. We anticipate that interim results from the TB 99 survey will be available in 2004. These will give an indication of the factors which might place a herd at an increased risk of TB and could therefore provide a basis for identifying measures to be implemented to reduce this risk.

4.6.4 Short, medium and long term options to manage infection in badgers need to be considered. In the short term (1-3 years), in the light of the evidence we now have on the effect of reactive culling as carried out in the RBCT, efforts may have to focus on farm or habitat management including herd health planning to seek to reduce contacts between badgers and cattle. In the event of scientific evidence from the RBCT that proactive culling of badgers is effective in reducing incidence in cattle, the medium term (3-5 years) option might encompass practical badger culling/management strategies. This might have a marked effect on reduction of TB in cattle, if culling is severe enough. With the prospect of a practical vaccination strategy (for badgers or cattle) still being several years away vaccination remains a longer-term aspiration.

4.6.5 Any new policy options require evaluation in terms of costs and benefits. Data generated from scientific investigations may be used to inform future decision making through computer modelling.

4.6.6 Questions:

) Do you agree that, in the light of current evidence, policies should be developed (including badger culling) that seek to control transmission of bovine TB between badgers and cattle?QUESTION 7(

) Should we consider introducing, in conjunction with badger control/management, better controls on the disease in cattle using for example, the gamma interferon test?QUESTION 8(

4.7 Badger management / control

4.7.1 Defra have now effectively ruled out reactive culling in England in the way in which it was carried out in the RBCT as a policy option. We do not yet have a scientific explanation of the recent interim findings of the RBCT that showed reactive culling of badgers to increase the number of TB affected herds by 27 per cent compared with the control areas. But one possibility might be 'perturbation' - that is, the increase in cattle TB results from the disturbance caused to the badger population by removing a portion of them. This could lead to increased movement by infected badgers, or uninfected badgers moving to areas from where infected badgers have been removed. The proactive culling treatment in the RBCT is continuing.

4.7.2 Research is also being carried out in the Republic of Ireland to ascertain the effect of badger culling over large areas on the incidence of bovine TB and Government will consider the policy implications of the results for GB. When the results are published, the ISG will be asked to consider the implications and advise Ministers. It should be noted that the Irish approach differs significantly to the RBCT in that they have used snares as opposed to traps and there is no 'survey only' control group with which to compare the culling treatment.

4.7.3 There are a number of outstanding possible outcomes of the RBCT:

(a) Proactive culling of badgers in the form implemented in the trial is demonstrated to substantially and consistently decrease incidence of TB in cattle.

4.7.4 In this case, it will be important for all the issues relating to deployment of an effective badger management strategy in high TB incidence areas to be examined, taking into account the method and means of capture, while recognising the legal protection afforded to badgers.

4.7.5 We would need to review trapping and culling methods to assure ourselves that whoever was conducting these operations would be using the most effective and humane methods.

4.7.6 Any proactive culling policy would require adopting an area or regional approach to TB management.

incidence of TB in cattleincreaseb) Proactive culling of badgers in the form implemented in the trial is demonstrated to substantially and consistently

4.7.7 Reactive culling as carried out in the RBCT has been shown to have this effect over the period of the trial so far. This has demonstrated the potential for badgers to transmit TB to cattle in certain situations, since the disruptions caused by culling seem to have increased the risk to cattle despite the decrease in badger numbers. The proactive culling treatment removes about 80 per cent of badgers in a trial area. In the event that this level of reduction in badger population increases TB incidence consideration would need to be given to other strategies, such as the deployment of an effective badger vaccine, that could reduce the prevalence of TB in badgers and subsequent transmission to cattle without disturbing the badger population. Alongside these, there would be a need to strengthen cattle control measures.

4.7.8 In this case, and in the case of c) below, consideration will also need to be given to whether more effective culling techniques might be employed in any culling policy to ensure a beneficial effect on bovine TB in cattle.

c) Proactive culling of badgers in the form implemented in the trial is shown not to substantially affect TB incidence in cattle.

4.7.9 Although this result would not demonstrate that badgers play no role in TB in cattle, particular consideration will need to be given in this case to putting more emphasis on cattle based controls, including in relation to biosecurity, use of gamma interferon, and pre and/or post movement testing.

4.7.10 Furthermore, vaccine research may need to be focussed more on vaccines for cattle than on vaccines for badgers. This is because a badger vaccination is likely to be less effective than culling in reducing incidence of TB in cattle. The recent report by the ISG Vaccine Scoping Sub-Committee reviews, in depth, the implications of implementing control strategies based on cattle and/or badger vaccines. Whilst effort may focus on the development of a cattle vaccine plus a diagnostic test that distinguishes between vaccinated and infected animals, persistent infection in wildlife may pose problems if vaccinated animals, even if fully protected, respond positively in a diagnostic test after exposure to challenge infection. In addition, it is important to recognise that effective cattle vaccination would be difficult to achieve if the challenge from infected wildlife was too great.

4.7.11 Under these circumstances farm businesses in high TB incidence areas might need to consider the long term viability of remaining in cattle production.

d) Proactive culling of badgers in the form implemented in the trial is shown to have different effects on TB incidence in different areas.

4.7.12 If the variation in the impact of culling can be explained by statistical analysis of different attributes of the trial areas then this result could suggest in which areas badger management might be effective and in which areas it might not be. If the variation in effectiveness within the RBCT cannot be explained, then no clear policy on badger management is indicated. However, in this case, given the scale and scientific design of the RBCT, it is questionable whether a subsequent badger management strategy based on culling or vaccination of badgers could be expected to consistently decrease incidence in cattle.

4.7.13 Questions:

) Under what circumstances would a badger culling or management policy be acceptable?QUESTION 9(

) How would any badger management/culling be organised, monitored and evaluated? Who should pay?QUESTION 10(

4.8 What role could vaccines play?

4.8.1 Practical application of vaccine for cattle or badgers remains a long term prospect. The TB strategy needs to consider how a vaccination policy might be developed and delivered and the role of field trials.

4.8.2 Badger vaccine. If shown to be possible, the development of better means of identifying groups of badgers or individuals that are likely to be excreting M. bovis, may provide a good case for proposing a combination of selective culling (taking perturbation effect into account) with vaccination of contacts or nearby groups at risk. Modelling studies suggest that as culling is more effective in eradicating disease from the badger population than vaccination, a combined strategy (of culling and ring vaccination for example) would be likely to be more efficacious than vaccination alone. This and other delivery strategies are discussed in the Report of the ISG Vaccine Scoping Sub-Committee.

4.8.3 In line with the principles of the AHWS we would need to assess the costs, risks and benefits of this approach, including the need for small scale field experiments or feasibility studies prior to large-scale field research to measure the effect on cattle.

4.8.4 Cattle vaccine. Although the use of cattle vaccines is theoretically possible, there are at present constraints on its use in relation to EU trade requirements, variable efficiency of available vaccine, and the inability to differentiate vaccinated cattle from cattle which have been exposed to natural infection (with or without vaccination). Consumer acceptability of food products from vaccinated animals could be an issue. Together, these constraints make it unlikely that a cattle vaccine against TB can be used in the near future, though it remains a longer term prospect.

4.8.5 Question:

) On the basis of scientific evidence to date, how should Government focus research efforts on vaccines? Wider views on the prospects for vaccination would be welcomed.QUESTION 11(

4.9 Improved diagnostics

4.9.1 The nature of TB (chronic and intracellular) makes it an inherently difficult disease to diagnose in both man and animals. In Member States where the organism which causes avian tuberculosis is not very common the single intradermal tuberculin test with bovine tuberculin alone is the primary test for the diagnosis of TB in cattle. It has been estimated that 6 to 12 per cent of all cattle in the UK and Ireland would be classified as reactors to the single intradermal test used in the rest of the EU. Consequently, for many years it has been the practice in the UK and Ireland to use the intradermal comparative test with avian and bovine tuberculins. This reduces the number of false positive test reactors. While recognised as a good herd test, the tuberculin test has limitations for identifying individual infected animals and will leave a proportion of infected animals in the herd. A test is not available that has 100 per cent sensitivity.

4.9.2 Any test based on detection of excretion of M. bovis or the presence of antibodies, will lack sensitivity, i.e. not all infected animals will be detected.

4.9.3 The gamma interferon test is permitted under EU law as an adjunct to the tuberculin skin test in cattle. It is a rapid and practical test and has potential to detect animals at an earlier stage of infection, but has slightly lower specificity than the skin test used in the UK. It is also more costly than the skin test. It may, in time, be possible to increase the specificity of the gamma interferon test by including recently identified antigens in the test.

4.9.4 In October 2002 a field trial was established to evaluate the cost effectiveness of using the gamma interferon assay in field conditions alongside the skin test. It is designed to test the hypothesis that, in confirmed multiple-reactor TB breakdowns, the removal of animals reacting to a gamma interferon test carried out between the disclosing and first short interval tests will shorten the time a herd is under restrictions. It will also determine whether a more stringent interpretation of the first short interval test would have an effect comparable to that of the gamma interferon test. The trial needs 600 herds to allow detection of significant differences between treatments. The current recruitment rate of participating herds is lower than anticipated so it may take several years before we can conclusively say whether parallel gamma interferon testing offers any real advantages over the current testing regime for reactor herds.

4.9.5 Meanwhile, we have already introduced the use of gamma interferon to resolve suspected cases of non-specific reactions (NSR) to the skin test as a decision making tool when considering whole or partial herd depopulation.

4.9.6 The development of a rapid live badger diagnostic test would permit badger management action to be targeted on infected animals . Two types of immunological assays are under development. The first detects antibody responses to M. bovis and is an improved version of the existing Brock ELISA, allowing detection of about 60 per cent of all infected badgers. It is quick and easy to use in the field but tends to detect only those badgers with advanced infection. Work to validate the test should be completed by the end of June 2004. The second assay under development detects cellular immune responses to M.bovis, using the principle of the gamma interferon test for cattle. The advantage is that it is much more sensitive because it will detect badgers at all stages of infection, but the disadvantage is that it requires 2-3 days to complete. The assay is still undergoing optimisation for use with badger blood. The target is to complete this by December 2004. Test validation should take a further 6-12 months.

4.9.7 Question:

)QUESTION 12( How should the gamma interferon diagnostic test for cattle be used or developed in GB - to reduce the time herds spend under restriction by increasing the number of animals taken as reactors, to deal rapidly with herd breakdowns outside existing TB hotspot areas and/or to distinguish between vaccinated and infected animals?