Select Committee on Agriculture Minutes of Evidence


Memorandum submitted by the Independent Scientific Group on Cattle TB (J11)

INTRODUCTION

  1.  In our memorandum of February 1999, we explained that the Independent Scientific Group on Cattle TB (ISG), established as part of the Government implementation of the Krebs report on bovine tuberculosis in cattle and badgers [1], was encouraged to take a holistic view in the search for a sustainable scientific base to underpin future control policies while recognising that the elimination of badgers from large tracts of the countryside is not an option for future policy. We identified the need to understand the epidemiology and pathogenesis of TB in cattle and badgers better and the MAFF programme of research, of which the field trial is a part, has been designed to achieve this. Implicit in our approach is that our primary focus is, and shall remain, on the establishment of the science base, but we accept that any future control policy will have to take account of social and economic factors as well as being environmentally sustainable.

BACKGROUND

  2.  Past control policies have included the testing and slaughter of infected cattle (as at present) and various levels of badger removal (in the past). The effectiveness of these policies has been criticised to varying degrees by both farmers and conservationists.

  3.  The evidence to link badgers to bovine TB in cattle is based, principally, on the observed incidence of infection of M. bovis in badgers inhabiting affected areas, coupled with the finding that some early badger removal strategies appeared to result in a decreased incidence of cattle TB. Krebs concluded that "the sum of evidence strongly supports the view that, in Britain, badgers are a significant source of infection in cattle". However, Krebs also recognised the lack of unambiguous scientific data to support that view.

ISG APPROACH

  4.  As is described in detail in our second report to the Minister of Agriculture, Fisheries and Food [2] the Group has developed a wide-ranging epidemiological investigation into TB in both cattle and wildlife. Our approach has been to identify the major questions that need to be addressed and how answers can best be found in order to inform policy development. Major questions relate to factors influencing the prevalence and persistence of the disease in cattle and wildlife, risk factors contributing to the development of the disease in cattle, transmission routes between and within species, the use of effective diagnostic techniques and the effectiveness and economic value of potential control options.

  5.  Currently, a lack of investigative tools for studying the epidemiology of TB in wildlife means that the field trial is the only method by which the ISG can collect much of the essential epidemiological information, and relate the underlying pattern of TB infection within the badger population to the incidence of TB in cattle. It is also the only way of quantifying the contribution of badgers to cattle TB and of determining if culling badgers is an effective way of controlling TB in cattle. It is essential to find an effective and acceptable way to control cattle TB in the long term. Failure to complete our work successfully could leave the whole issue in limbo for a further extensive period.

PROGRESS

  6.  In our previous memorandum to the Committee and again in our second report we defined the questions that needed to be addressed and set out our strategy for obtaining the information necessary to answer those questions. In summary, there are six elements to this multi-faceted investigation, ie:

    (i)  the field trial;

    (ii)  a questionnaire based epidemiological survey;

    (iii)  studies into cattle pathogenesis;

    (iv)  a road traffic accident survey;

    (v)  evaluation and analysis of existing data; and

    (vi)  other related research.

  Progress made on each of these elements from the Group's perspective is summarised below.

(i)  The field trial

  7.  After a difficult initial period when delays occurred in the implementation of trial operations, the Group is broadly content with the subsequent progress that has been made with the conduct of the trial. All of the 10 triplets which comprise the trial areas have now been selected and announced. Five of the 10 triplet areas have now undergone initial, proactive culling operations and by the end of the calendar year initial proactive culling should have been carried out in a further two triplets. This follows the projected timetable presented in our second report. The remaining three triplets are planned to undergo initial culling operations in 2001 and work to survey these for badger activity has been put in hand.

  8.  We continue to monitor culling effectiveness in proactive areas and we are confident that, with the exception of one triplet, operations are achieving an acceptable badger clearance rate.

  9.  The flow of post mortem examinations on badgers trapped and culled in trial operations was halted in 1999 when the Health and Safety Executive raised concerns over the level of protection available to post-mortem staff against the risk of contracting M bovis infection. Enhanced facilities had to be installed, resulting in delays to the post mortem programme. As a result some badgers had to be frozen and kept for later post-mortem. The backlog of frozen badgers was cleared before culling recommenced in May 2000.We have commissioned research to be carried out to check that the effects of freezing badgers does not skew the data obtained from post mortem of frozen carcasses.

  10.  Strategies for the most effective use of staff for work in reactive, and follow-up culling in proactive areas, have been re-considered and refined as necessary to ensure that badger populations are kept low in proactive cull areas and that the removal of specific groups in reactive areas is effective.

  11.  Co-operation from farmers in trial areas remains high, typically around 80 per cent, despite a high level of protest activity in places. Ministers and their officials are working hard to encourage continued high levels of farmer involvement and to ensure the general public are better informed of the reasons for the trial, the necessity for killing badgers as part of the trial design, and the objectivity and balance of the research programme. This should go some way to counter negative publicity generated by opponents who focus solely on the trial.

Animal Welfare

  12.  We remain aware of the need to demonstrate our commitment to ensuring that trial operations are conducted in a way that minimises suffering and maintains high levels of animal welfare. Standard operating procedures are set to ensure that captured animals remain in traps for as short a period as possible, that badgers are killed humanely and that non-target species are released unharmed where possible.

  13.  An audit of the procedures for despatching badgers has been carried out by MAFF internal auditors and by an independent auditor appointed by MAFF. We welcome the principal finding of the independent auditor's report that the procedures adopted by MAFF field staff meet the humane ideal of painlessly causing instant death or permanent loss of consciousness until death, and his recognition of the weight that welfare issues are given in the planning and conduct of trial operations. Members of the ISG closely observe field activities.

Auditing

  14.  Apart from the audit on the humane despatch of badgers mentioned above, the group has encouraged the setting in place of audits eg covering aspects of field operations including sett surveying accuracy, territory delineation and trapping efficiency. A post hoc check is also carried out by ISG members to assess the efficiency of badger removal in those trial areas subject to proactive culling.

  15.  In addition, MAFF have just put in hand an audit of the statistical power of the trial's design as recommended by the Committee. The Group has submitted a report to the Independent Auditor to assist his assessment. This is attached at Annex A.

Data analysis

  16.  Work has progressed from planning to implementation. Procedures to ensure reliable data collection and comparison across all trial areas have been developed. A large amount of data is beginning to accrue and will need careful analysis and interpretation.

  17.  Key to this will be the comparison of data from the three types of trial area, proactive, reactive and survey only, and comparison of herd breakdowns (allowing for differences in numbers of farms, herds and animals); badger activity and TB prevalence and other factors.

  18.  The first interim analysis is due to start in the near future, when 100 breakdowns in triplet areas have been confirmed. This, and future data analysis work, will be carried out by Research Assistants working under the direction of the Group's Vice Chair, Dr Christl Donnelly, with the involvement of Group members. Further interim analyses will be carried out thereafter at about six-month intervals.

Additional Work in Trial Areas

  19.  There are a number of other studies that are ongoing in trial areas running in parallel with the field trial:

    —  the ecological consequences of removing badgers from trial areas. This study should reveal valuable data on the impact of badgers on other species, both birds and mammals, in an area;

    —  genetic analysis of badgers;

    —  estimation of badger numbers from field signs in trial areas;

    —  the effect of badger removal on badger social organisation;

    —  the possible role of other wildlife on cattle TB;

    —  strain typing of all M. bovis isolates from trial areas, using a range of typing methods.

(ii)  Questionnaire-based epidemiological survey

  20.  An objective and comprehensive assessment of the factors which predispose herds to a TB breakdown and their relative importance is essential. It is our view that this can best be achieved by surveying a large number of cattle farms using a structured questionnaire. In designing the questionnaire we were guided by a number of principles:

    (a)  the need for objectivity;

    (b)  the need to be comprehensive;

    (c)  the need to provide data amenable to statistical analysis; and

    (d)  the need for practicability.

  21.  The TB99 epidemiological questionnaire has been deployed in the field for more than 18 months. It has collected invaluable information on a range of risk factors, such as herd composition, cattle movements, farm management practices, and the presence of potential wildlife sources of TB infection. The questionnaire and its implementation has been well received. A review of its design, based on field experience, currently taking place suggests only minor modifications. The Group was concerned to learn that use of the TB99 form had been halted temporarily as a result of the demands currently being made on the resources of the State Veterinary Service by the Classical Swine Fever (CSF) outbreak. We have strongly advised MAFF that the use of the questionnaire in trial areas is critical and should be resumed immediately, even if it cannot be used elsewhere in the country at the moment. An initial analysis of TB99 data will be made after 100 breakdowns in trial areas.

(iii)  Cattle pathogenesis studies

  22.  The successful control of bovine TB in most of Great Britain based on the slaughter of infected cattle identified by regular tuberculin testing, coupled with movement restrictions when reactors are found in a herd, has been interpreted as evidence for the existence of a wildlife reservoir of infection in areas where TB control using these measures has not been achieved. This may or may not be true, but we believe that there is a need to question, in these high risk areas, whether control of the disease is constrained by limitations in current testing procedures and whether cattle-to-cattle transmission is contributing to disease transmission and persistence in herds.

  23.  The Group attaches a high priority to answering these questions and to knowing more about the dynamics of the disease in cattle and its temporal relationship to diagnosis, transmission routes and the effectiveness of early diagnosis. We are pleased that MAFF has funded a major pathogenesis study involving laboratory-based investigations on experimentally-infected animals linked to a field study of naturally TB-infected cattle.

(iv)  The Road Traffic Accident Survey

  24.  We recommended that valuable data on the prevalence on TB in badgers could be obtained from a road traffic accident (RTA) survey. We proposed a survey of badgers found dead at roadside, to be carried out in seven counties: Cornwall, Devon, Gloucestershire, Herefordshire, Worcestershire, Shropshire and Dorset, plus badgers found dead on farms in trial areas. We are concerned that, while plans for the survey have been in development for some time, the start of the survey has been further delayed. We have urged MAFF to take steps to minimise the delay in implementing this part of the programme.

(v)  Analysis of historical TB data

  25.  Analysis has begun of data held by MAFF on past TB breakdowns and badger removal operations. This should contribute to our understanding of the dynamics of the disease in cattle and badgers.

(vi)  Other related research

  26.  The Group advise MAFF on the content of its wider research programme on TB. There are major programmes in place on improved diagnostic tests, improved tools for molecular epidemiological studies and on TB vaccine development. The joint MAFF/Wellcome Trust Foundation-funded project sequencing the M. bovis genome, which is in progress at various centres of excellence in the UK and abroad, is expected to be completed soon and should pave the way for further advances in understanding the epidemiology and pathogenesis of tuberculosis.

  27.  In our second report to the Minister we recommended that MAFF should commission studies on the economic impact of the disease, both at farm level and in the wider agriculture industry, and on the economic evaluation of policy options for the control of TB. This recommendation was implemented by MAFF in its Research Requirements Document for 2000 and the Group is assisting the Ministry in its assessment and selection of suitable projects in this area from the proposals submitted.

TB FORUM

  28.  The ISG and the National Farmers Union recommended that consideration be given to the establishment of a forum of interested parties to meet, discuss and plan what could be done in the short term to control cattle TB by focusing on "cattle" options. We are pleased that MAFF established the TB Forum in December 1999 and we are happy to play an appropriate part in it.

CONCLUSION

  29.  Considerable progress has been made, notably on the field trial, on the epidemiological survey and on the TB-related research programme, since the Committee last reviewed the Government's strategy for the control of cattle TB. The Group is indebted to MAFF and its agencies, in particular staff at the Wildlife Unit and the Veterinary Laboratories Agency, for their work in support of the Group's objectives. We are also very appreciative of the consistent support shown by MAFF Ministers for our work.

27 October 2000

REFERENCES

  1.  Bovine Tuberculosis in Cattle and Badgers. Report by the Independent Scientific Review Group (Chairman: Professor J Krebs FRS). MAFF Publications, 1997.

  2.  An Epidemiological Investigation into Bovine Tuberculosis. Second report of the Independent Scientific Group on Cattle TB (Chairman: Professor F J Bourne MRCVS). MAFF Publications, 2000.


 
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