Preparing for a new TB Strategy on bovine tuberculosis

Preparing for a new TB Strategy on bovine tuberculosis

The Royal Society of Edinburgh (RSE) is pleased to respond to the Scottish Executive Environment and Rural Affairs Department (SEERAD) consultation on preparing for a new TB strategy on bovine tuberculosis (bTB). The General Secretary, Professor Andrew Miller, and the Research Officer, Dr Marc Rands have compiled this response, with the assistance of a number of Fellows with expertise in this area.

TB is a major disease of UK cattle which has increased enormously since 1996 when as few as 1.3% of cattle herds tested resulted in a confirmed incident. Provisional figures for 2003 indicate that as many as 3.4% of herds tested resulted in a confirmed incident. The seriousness of the problem becomes more apparent when it is recognised that in 2003 around 58 thousand herd tests were performed involving 4.5 million cattle tests, of which 23,000 cattle were compulsorily slaughtered. In any year around 5 thousand herds remain under TB movement restrictions. It is interesting to note that the apparent linear trend in the percentage of confirmed incidents from 1996 to 2000 would suggest that the incidence in 2003 should have been higher, and it is not yet clear what has been the effect of FMD in 2001 on testing for incidence.

There are several distinctive characteristics of TB which make it unique and explain why it has it has become an intractable problem:

a TB is remarkably difficult to diagnose in cattle and wildlife. The tuberculin skin test used to test cattle is known to have poor sensitivity (the proportion of true positives detected by the test is reported to be around 70 to 80%) and the consistency of this test is questionable. There is some hope that additional testing using the new interferon-gamma test will improve this sensitivity but this is not likely to be good enough for all TB infected animals, to allow the test to accurately identify TB in herd testing. Diagnosis is further complicated by animals often showing very few signs of the disease, with accurate diagnosis only being possible at post-mortem and the disease often only presenting in a small number of animals in the herd.

b The TB transmission process is poorly understood. For some time it was largely believed that transmission was principally from badgers (or other wildlife) to cattle, and that there was relatively little cattle to cattle transmission. The recent weight of scientific studies now indicate that TB is both a disease between and within cattle and badgers, and so in addition to it being spread from badger to cow, it is also spread from cow to cow and from badger to badger. The number of incidences in herds is likely to have been considerably increased in recent years by the considerable movements that take place of cattle to and from herds. Consequently, the proposals in the Paper to reduce the risk of spreading TB from one herd to another by requiring pre and post movement testing in GB herds is a priority. Nevertheless this is not a fail-safe proposal due to the poor sensitivity of the test procedures.

c Any success in reducing the incidence of TB in cattle by movement restrictions will always be under threat from reinfection from wildlife sources. It is recognised from culling operations and Road Traffic Accidents monitoring that TB incidence in badgers has been on the increase. Any long-term solution must make provision for a healthy badger population.

d TB has generally been associated with certain geographical hotspots and this has been reflected in the TB cattle testing regimens. However, it is likely that once a hotspot has become established, then increased testing in these areas will do little to stop the disease spreading. These hotspot areas were originally confined to the South West of England but with the increase in TB incidence, the disease has become more prevalent in northern areas. The reason why certain areas become hotspots is unclear but it is likely to be a consequence of chance events whereby infection is spread to cattle from infected badgers and/or infected cattle are bought into herds. This means that all areas outside the hotspots are potential hotspots as long as there are unrestricted cattle movements and there are infective wildlife sources. Increased testing should be carried out in areas outside the hotspots in order to prevent the disease becoming established and actions taken in the event of the disease being detected, such as the compulsorily slaughter of all animals in the herd. The new GB strategy acknowledges some of these concerns with the adoption of a zoning principle.

e The prospect for controlling TB in cattle or badger populations using vaccinations remains distant. As stated in the recent report of the Independent Scientific Group (ISG) Vaccine Scoping Sub-Committee (Defra July 2003) there are "significant scientific hurdles that have to be considered and overcome, even to get to the point of conducting a field trial".

f The recent finding reported by the ISG on Cattle TB (November 2003) produced the interesting result that the reactive culling treatment in the Randomised Badger Culling Trial (RBCT) led to an increased incidence TB in cattle herds compared to matched triplets where no badger culling was applied. This not only reflects the complexity of the epidemiology and challenges the wisdom of reactive culling as a policy option, but also strengthens the case for the RBCT to be continued until results of the proactive treatment are available.

Scotland is in a unique position in the UK having experienced only 21 incidences of TB in 2003. However, if TB cannot be brought under control within England and Wales it is inevitable that TB hotspots will develop. Once the disease becomes established in the Scottish national herd, its control will be extremely expensive and its eradication problematic. Infections are likely to be brought about by cattle movements from outside the UK and other UK areas, or from infectious wildlife sources such as badgers or deer as the disease moves north in these species. By the time the disease is detected it will have had an opportunity to spread to other herds and wildlife populations. Currently, Scotland benefits from a low density of badgers but with badger populations increasing in the UK this advantage will be lost.

It is therefore imperative that Scotland should become more vigilant and increase testing of herds and be prepared to take appropriate actions in the event of herds testing positive. In addition, awareness and biosecurity should be widely promoted on all farms in order to minimise the contact animals have with wildlife, to decrease the contact cattle have with other cattle groups on the same premises, and most importantly for farmers to be circumspect about market/farm purchases.

In addition, Scotland has always enjoyed a strong reputation for research in the animal sciences. It is important that SEERAD encourage collaborative research into TB research and ,in particular, monitoring wildlife at risk of TB for signs of infection, understanding the pathogenesis of TB in cattle, identifying a potential vaccine for badger and cattle populations, and understanding the epidemiology of the disease in order that it can be rapidly brought under control in the event of hotspots moving north.

The specific questions in the consultation paper are now addressed below:

Establishing a vision

1: 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?

Scotland is in the fortunate position that so far no wildlife reservoir has been found for M.bovis. Although eradication of TB in cattle across the UK may not be possible within 10 years we believe that supplementing current regulatory framework with improved surveillance testing and biosecurity could make it possible for Scotland to achieve and maintain TB - free status in this timeframe. We firmly believe that TB be progressively reduced and that Government should continue to fund research and develop the science base in the UK to inform future control strategy.

From Fig.2 (p19) which shows the predicted rise in expenditure on TB and the accompanying text which notes that this is predominantly related to control costs, it would seem sensible to increase the research budget two or threefold over the next few years in an attempt to alter the control cost profile. Even if the additional research effort was only minimally effective in bringing about an improved disease situation, the increase in research cost would be easily offset by the proportionate reduction in the costs of control measure at that time. Another effect of making more money available for research could mean that the long-term liability to the Government and the producer would be less. This may shift the balance of costs set out in the Regulatory Impact Assessment.

2: 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?

If limited resources are to be applied optimally, there should be regional differentiation to allow more stringent quarantine measures to be implemented in areas where disease does not exist already or its prevalence is low, and where remaining free of the disease is important. This is in the interests of all regions and should also help TB-infected areas to be come TB-free faster.

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

In the ten-year vision, the aspirations should not only be to have TB free cattle but also to remove the threat of TB from wildlife. Since it is likely that there will need to be long-term commitment of public funds in relation to TB control (and eradication if possible), at least in relation to research effort, societal acceptance of these aspirations is important. In this context, the public increasingly want to know the facts on which decisions are based.

Rationale for Government intervention

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

While one could take the view that TB is inevitable and does not need to be controlled on the grounds that the cost of the disease is not as great as the cost of the control of the disease. This "do nothing" option is not realistic as there are no commercial solutions for the control of TB in cattle and it would be unacceptable to have cattle and wildlife suffering from TB and the presence of the disease would destroy consumer confidence in the quality of milk and beef products. Moreover, bovine TB is a potential zoonosis (a disease communicable from animals to humans under natural conditions) and would remain a potential threat to public health.
The ultimate objective should be to eradicate the disease. Keeping the country free of TB thereafter should be less difficult than keeping the country free of FMD due to the differences in dynamics of disease transmission.

Balancing costs, benefits and risks

5: Who in your opinion are the main beneficiaries of current bovine TB controls?

The beneficiaries are (i) the public, in view of the threat to public health (although this is small), and in respect of wildlife and the environment, and (ii) the farmers who appropriately receive compensation for a disease which they are unable to control, and who have to see thousands of their cattle slaughtered each year because of TB.

6: What contribution should the farming industry make to reduce the risks to their herd of bovine TB?
    
Farmers are justifiably disillusioned by the progress made on controlling TB but this is because it is so far an intractable problem to which scientific solutions are not yet known. However, there are clear signs that farmers may be able to practice different management techniques which will provide greater biosecurity for their herds, for example double fencing, and appropriate and meaningful quarantine for incoming livestock. It is imperative that they pursue these avenues and not precede on the basis that it is a disease outwith their control.

Development of future policies

7: 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?

It is clearly important to develop policies that seek to control the transmission of TB between badgers and cattle. This would be predicated by a better understanding of the routes of transmission and, for example, the profile of indirect transmission of infection. It is therefore important that the RBCT continue in order to provide an answer to the potential role of proactive culling as a strategy option.

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

Yes, diagnosis is the key to controlling TB. If tests were available that could accurately identify infective cattle, then the disease could rapidly be bought under control and managed. The most sensitive tests available should be adopted in order to identify infected animals at an early a stage as possible, ideally before animals become excretors. Equally, tests with an excellent negative predictive value will be needed to support biosecurity measures when new animals are introduced.

Badger management / control

9: Under what circumstances would a badger culling or management policy be acceptable?

Wide scale badger culling would only be acceptable if:

   1. the evidence showed badgers as being the main source of M. bovis infecting cattle,
   2. vaccination was not an option because of lack of suitable vaccines and difficulty/expense of vaccination,
   3. the evidence was convincing that culling would reduce the incidence of TB,
   4. the reduction in incidence could be demonstrated to be sustainable,
   5. healthy badger populations could be expected in the future,
   6. there could be confidence in Defra successfully managing such an implementation,
   7. the economic case was clearly demonstrable and the overall scientific case was sound.

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

The practical aspects of a management or culling programme would need to be based on knowledge of badger behaviour and seasonality. At present, little is known regarding the cattle to cattle and badger to cattle transmission and more information would be welcome to design control strategies and improve mathematical models.

Any badger management would best be undertaken by a Government agency, especially as it would likely attract considerable public disapproval even if the premise in Q9 were correct. It will be important that any culling should be carried out humanely. Such constraints can, however, affect the efficacy of such culling as evidenced in the RBCT where total removal of badger populations has not been possible using humane cage trapping.

What role could vaccines play?

11: 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.
    
Vaccines should be the long-term goal for both cattle and wildlife and there are good examples of an effective vaccination programme for wildlife species. Current work with badgers in the Republic of Ireland may shed some light on this but an important aspect will be how the vaccine could be delivered. The lack of progress on a cattle vaccine is disappointing after so many years of research but reflects the difficulty of working with such a complex organism. Greater support needs to be given to researchers working in this area.

Improved diagnostics

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?

The IFNγ test, once it has been properly evaluated, should be used primarily to enhance the ability to deal rapidly with herd breakdowns. The value of distinguishing between vaccinated and infected animals will be important if international trade can be allowed for vaccinated animals.

It will also be important to develop tests that identify challenged (recently) but already immune animals. Diagnostic antigens are available that can distinguish between vaccinated and naturally infected cattle and with the availability of the M.bovis and M.bovis BCG genome sequences there is potential to identify more. These antigens and tests need to be evaluated in a field situation over a longer period of time.

Surveillance Testing

13: We have proposed measures that are aimed to improve our surveillance testing and make the system more transparent. Are these measures appropriate?

The measures proposed to improve surveillance testing are realistic and appropriate but may not be sufficient. Increased testing in areas where TB has not occurred might help with early detection but any disease surveillance will need swift and appropriate action in the event of disease detection.

Pre and Post Movement Testing

14: What are your views on our proposal to reduce the risk of spreading TB from high to low incidence areas by requiring pre and post movement testing of all cattle moving from 1-2 year testing herds to other herds?

The TB strategy for Scotland must focus on protecting Scotland from imported disease from known high TB incidence areas, based on epidemiological advice. We therefore support the proposal that a legal requirement should be introduced to require pre and post movement testing for which the industry may be required to pay. This will be important to improve detection; prevent movement of disease on to and off farms; and promote more awareness of TB biosecurity amongst farmers. For example, it should be examined whether the re-stocking of farms where cattle were culled during the 2001 foot and mouth outbreak in South West Scotland has resulted in new cases of TB, as quite a few farms re-stocked from areas in England now known to be 'hot spots'. However, this would not be a concern if pre and post testing had been introduced prior to the restocking.

15: What are your views on our advice that farmers should themselves apply post-movement testing in order to minimise the risk of transfer of disease from high to low incidence areas?

Post-movement testing as part of a requirement for release from quarantine should be supported. Without knowledge of the full disease scenario, it is not clear what degree of integration with different classes of resident stock can be permitted for brought-in animals to avoid disease introduction to a herd. For example, quarantining incoming animals amongst a group of animals destined for slaughter within a given time window may be acceptable whereas integration with the breeding herd would not.

16: What are your views on the other options considered?
    
Strong consideration should be given to zoning and pre and post movement testing for all cattle sold for breeding or production based on sound epidemiological principles. Consideration should also be given to the use of embryo transfer for introducing new genetic material.

Summary

In summary, the preparations for a new GB strategy on bovine tuberculosis are sensible and the minimum that could be expected in the face of what is a highly persistent disease. However, they should be considered as policy options under test as it is not possible to tell if they will provide a basis for driving down the incidence of TB. In this context, the strategy needs to be prepared to adjust and adopt new approaches in the light of early results from implementing the new strategy.

The situation in Scotland is also very different to England and Wales. The climatic conditions may be less favourable to the survival and spread of the organism, wildlife hosts may not be so prevalent and, as was demonstrated in the FMD outbreak, Scotland was able to marshal an effective control policy. There is, therefore, every opportunity to stop the disease spreading in Scotland providing it can be detected early enough and it is important that SEERAD develop a customised strategy for use in Scotland that is complementary to that in England and Wales but which can take advantage of these differences.
Additional Information

In responding to this consultation the Society would like to draw attention to the following Royal Society of Edinburgh publications which are of relevance to this subject: Inquiry into Foot and Mouth Disease in Scotland (July 2002) and Preparing an Animal Health and Welfare Strategy for Great Britain (April 2003).

 

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