Contingency plan for the possibility of BSE in sheep

Contingency plan for the possibility of BSE in sheep

The Royal Society of Edinburgh (RSE) is pleased to respond to the Scottish Executive Environment and Rural Affairs Department consultation on a contingency plan for the possibility of BSE in sheep. The RSE is Scotland’s premier Learned Society, comprising Fellows elected on the basis of their distinction, from the full range of academic disciplines, and from industry, commerce and the professions. This response has been compiled by the General Secretary with the assistance of a number of Fellows with direct experience of agriculture and disease control.

The Society welcomes the proposed contingency plan, however, the risk analysis on which the contingency plan is based is itself founded on a number of unproven or untested assumptions. For example:

There is a degree of acceptance that the spread (although not necessarily the origin) of BSE in cattle was the ingestion of ‘contaminated’ meat and bone meal, and that this could have similarly affected sheep. However, the fact that experimentally sheep can be shown to develop BSE when fed (rather high) levels of BSE infected tissue does not provide evidence that sheep were infected with BSE at the time the cattle epidemic started.

It is assumed that if BSE did occur in sheep it would show similar clinical symptoms to scrapie, and therefore could potentially be obscured by that disease. However, there is little evidence, even experimentally, that BSE and scrapie will present in sheep with the same symptoms. Anecdotally, it is reported that the symptoms of experimentally induced BSE in sheep are not always similar to those of scrapie. There is the potential, therefore, that if naturally occurring BSE had been transmitted to sheep it might have been identified as a new sheep disease.

In experimentally induced BSE in sheep, the distribution of the infectious agent in the body is more widespread than in cattle, resembling the tissue distribution of the scrapie agent in sheep. Partly on this basis it has been assumed that BSE would be transmitted between ewes and their lambs (as scrapie can be). However, this assumption has not been tested.

If BSE had entered the national flock and passed from ewes to lambs there should be evidence of the infection in the present sheep population. To date tests on sheep have failed to find even one case of BSE, however, the number of tests that have currently been undertaken is not enough to rule out the possibility of BSE in sheep.

There is the assumption in the Plan that genetic resistance to scrapie conveys genetic resistance to BSE also. However, Professor Malcolm Ferguson-Smith, a member of the Spongiform Encephalopathy Advisory Committee (SEAC), has been reported in the Press as saying ‘it has already been shown that sheep resistant to scrapie are susceptible to BSE’. This is a point that must be clarified.

In order to take effective action to protect the human population, what is required is:

  • A clear cut diagnostics method for defining BSE in sheep
  • A system for tracking sources of infection, the origin of sheep meat and other products to specific farms/flocks.
  • Research on transmission routes of the disease.
  • Research on whether the sheep genotypes resistant to scrapie confer resistance to BSE infection.

Until results from these investigations are available, any preventative/surveillance system lacks a credible foundation. The specific issues identified in the Contingency Plan are now addressed below:

Action and Decisions Following Emergence of Test Results

The Food Standards Agency’s (FSA) suggested approach appears sound and flexible to adjust to unexpected occurrences. Unfortunately, the Contingency Plan has been overtaken by the widely publicised failure in certain key experiments. The failure of the experiment has a number of different consequences, for example, public confidence has been shaken by the exposure of weak laboratory procedures and has provided ammunition for those who will oppose implementation of a national slaughter plan. This may mean that in order to convince such people more than one piece of evidence might be required before implementation of the contingency plan. However, the Government will need to be completely transparent about any prolongation of the period of uncertainty.

Immediate Action Following the Onset of a BSE Crisis in Sheep

Protection of human and animal health
The precautions appear to be well thought out. However, in the absence of key elements of information about the natural development of BSE in sheep, it is difficult to be definitive about what to do about the entry of sheep meat into the food chain. The only risk free option would be to stop eating sheep meat, however, given the uncertainty over the level of risk involved, that option could appear to be disproportionate from a risk analysis standpoint. At the same time, given the potential widespread distribution of the disease agent in a sheep’s tissues, as compared with that in cows, there is unlikely to be any public confidence in consuming any sheep derived food material.

Because there is a question mark about the resistance to BSE of sheep that are genetically resistant to scrapie, the only viable approach to reducing the risk of the disease agent entering the food chain, other than testing, is to operate a sheep scheme equivalent of the over 30 months scheme. However, that approach makes the assumption that the disease reagent would not be detectable until the period at which clinical signs of the disease might begin to show, and that assumption has not been tested in sheep. Key issues, therefore, will be the development of tests to define meat as disease-free and the traceability of carcasses to source.

In terms of human and veterinary products, it would be reasonable to adopt a similar approach to sheep products as has been followed with cattle products. However, it is not clear whether the voluntary participation from marketing sources will ensure adequate disclosure about sheep and goat products. If prions are transmitted by ingestion, injection, inoculation, transplantation and/or transfusion, it seems that there may be one or two other sources of information and consultation which are not included in the list. For instance the Blood Transfusion Service could be asked to comment. A penalty for non-disclosure would certainly be another option

Full audit of the use of sheep- and goat- derived products outside the human food chain
The Society believes that the conduct of an audit, as outlined, would be a sensible way forward.

Communications strategy
With regard to the list of bodies that should be briefed following the emergence of a BSE crisis in sheep, the following UK bodies are also suggested: Animal Health Distributors Association; Animal Medicines Training Regulatory Authority; British Society of Animal Science; the Royal College of Veterinary Surgeons; the British Veterinary Society (only the Scottish Branch of the BVA is mentioned); and the Nutrition Society. The Society would also suggest that all six veterinary schools be added to the list. In addition, if there is a crisis, the lessons learnt from the foot and mouth epidemic suggest that farmers themselves need to be fully consulted and appraised from the outset.

European Union dimensions, and import and export controls in the event of a crisis
As BSE began to appear in the cattle of other Member States, the UK was faced with an unsatisfactory situation. Cattle carcasses were being imported that did not meet the UK safety requirements. There was a significant delay before this problem was addressed. Such a delay would be wholly unacceptable in the case of sheep meat. Therefore agreements must be gained at EU level to the contingency plan or the UK must be prepared to act in restricting imports, if that is required.

Slaughter and Disposal Programme if it Becomes Necessary to Slaughter at Least Part of the United Kingdom Flock
If there ever was a case for the total replacement of the UK sheep flock, then it could only be undertaken as a highly organised and structured operation. Its consequences would be far reaching both for food production and for environmental management of the hills and uplands, where sheep play a key part. Within that framework it might be temporarily necessary to divorce considerations of use of sheep for food production from use of sheep for environmental management. The adoption of a temporary non-breeding policy in some areas, to allow clean nuclear stock to be developed in others, might warrant consideration. If scrapie is of variable penetrance across the country, those areas with very low prevalence will resist the belief that BSE will be a problem in their flocks.

The proposal to formally commission a modelling project to examine ways in which the disposal exercise could be carried out should be supported. This would allow optimum strategies to be explored.

Managing the disposal programme
Following the Foot and Moth Disease (FMD), Government control over stock destruction is a sensitive area and it may be necessary to introduce new legislation to allow Government to develop a plan to deal with stock removal and destruction. However, it is essential for legislation to have arrangements for farmer consultation.

Existing legislation is fully adequate to deal with any issues of stock welfare, but it will be important for the process of stock removal and slaughter to be undertaken in an organised way, according to a well designed programme. Thought could also be given to preserving brain and non-CNS tissue from a variety of animals to provide material for future experiments.

If the programme were on the scale of the worse scenario, the process will need to be undertaken over a period of several years. However, the time should be kept as short as is feasible, so that the process of ‘rebuilding’ could be achieved within a foreseeable period.

Slaughtering arrangements
The slaughtering arrangements are highly important matters and will need to be considered and addressed through a close discussion of the issues with industry. There is need for a government/industry group through which these considerations of ‘disposal capacity’ can be addressed. This will be important not only in respect of a potential problem of BSE in sheep but also in relation to any other major disease outbreak.

Implications for the Farming Industry and the Rural Economy

Aid at slaughter
The scheme needs to find the balance between the needs for public accountability, speed and simplicity. It should provide full and fair compensation, and where there are pedigree stocks these should be recognised as having a higher market value (their replacement cost will be higher). With regard to animal weight, a simplified system based on bands of estimated weight would probably be acceptable both to government and to farmers i.e. the payment might be on 4 categories of stock by size.

In terms of the eligibility for aid, given the scale of the emergency that is being envisaged under this plan, it could be very time consuming and take a lot of effort and money to insist that all stock had to be inspected for other health issues, before being disposed of, to determine their suitability to enter the food chain under normal conditions.

With regard to payments for sheep that die while waiting for their allocated disposal dates, this will depend on the period over which the slaughter is carried out. If the period is a period of years, there would need to be allowance for stock which died during the period they were ‘held up’ in the scheme.

Retention aid
There should be a requirement for livestock to be managed at a conventional level of good practice for the slaughter compensation terms to apply, with satisfactory levels of animal welfare being a requirement for entry to the scheme.

Making payments direct to producers
With regard to the implementation of a registration system for sheep producers, it seems strange that the relevant information is not already available from the annual agricultural census. The main reservation is that the theoretical risk of BSE in sheepshould not be seen as an excuse for even further over-regulation of the livestock industry.

Casualty animals
It is difficult to envisage how the scheme would operate without help with disposal of casualty animals, as Government will wish to know how such animals are disposed.

Implications for related areas of the rural economy
Many of the more remote and fragile areas of Scotland depend on the sheep industry. Thus a major cull of animals would present serious economic challenges. However, these in their nature are no different from the challenges that have occurred as the profitability of the industry has fallen over the past six years. Therefore, the general policy approaches to deal with the problem are already developed.

Screening for ‘Safe’ Sheep and Segregation of their Meat from Potentially Infected Sheep meat

Allowing into the food chain only animals that have been tested for a Transmissible Spongiform Encephalopathy (TSE)
The initial need is for large-scale testing of sheep to establish whether there is any evidence that BSE is present in the national flock. This is an overriding consideration and should be undertaken as a matter of urgency.

If BSE is found to be absent then the issue of testing comes down to a consideration of scrapie. This latter disease has no record of transfer to man, but should be eliminated on the precautionary basis that it might theoretically ‘jump’ from sheep to man. As has been indicated earlier, there seems to be a question mark over whether scrapie resistant sheep are also resistant to BSE and many of the proposals in the Plan are based on the premise that animals homozygous or heterozygous for the scrapie resistant gene are resistant to BSE. This needs to be exhaustively tested before any plans are put in place.

Assuming that sheep TSEs turn out to be scrapie alone, there is a case for establishing a scrapie free national flock as soon as possible. The options to achieve this can be modelled biologically and financially to establish the most cost-effective approach. This is turn will influence the most appropriate methods of screening. High throughput genotyping methods could be readily devised and the time taken to obtain results significantly shortened. It is perhaps unfortunate that Government has not used the restocking of farms after FMD as an opportunity to introduce scrapie-free stock.

Identification
Identification and tracing of individual sheep presents an enormous practical challenge. However, if the Plan as outlined is to be put in place, a traceability scheme will be a requirement. However, all other options should be rigorously explored before individual animal traceability is introduced.
Would there be a sufficient commercial incentive to persuade the industry to market ‘safe’ sheep
It is not realistic to assume that there will be markets for ‘safe’ and for ‘unsafe’ sheep. If BSE is present in the national flock, there will be an initial market collapse followed by a slow rebuilding of consumer confidence through supermarkets selling ‘guaranteed safe’ sheep meat. There will be no market for sheep meat that falls into a category that is perceived as being ‘unsafe’.

In these circumstances, the market for home produced sheep meat would not operate effectively and, to avoid the environmental consequences of the disappearance of sheep from the land, the government could be forced into a degree of market intervention. This could involve payments for testing and for the establishment of identification systems, as well as payments for product price support.

Rebuilding the industry

Proposals for rebuilding the industry require further research to support them, particularly in regard to the suggestion that there might be environmental ‘reservoirs’ of infection, for example from pastures that had been grazed by a scrapie-infected heard. The underlying question is whether it is possible to eradicate BSE and/or scrapie from the UK (accepting that there may be a difference betweenthe two diseases). So far as BSE is concerned, the question is presently unanswerable. The origin of the disease - as distinct from its dietary route of spread - is conjecture. Similarly, there is no clear evidence about whether the BSE agent could/would exist in some ‘environmental’ host. However, by blocking the dietary route of spread, the disease is being rapidly brought under control and the annual number of cases in cattle is declining towards zero. Similarly the information on the origin of scrapie is equivocal. There are some claims that scrapie has re-infected ‘clean’ sheep introduced to farms after a programme of eradication. But there is also evidence of scrapie eradication programmes being effective in removing the disease.

Consideration could be given to the establishment of a scrapie and BSE Surveillance Unit, to parallel the work of the CJD Surveillance Unit. The model provided by the CJD Surveillance Unit suggests that one central dedicated facility is an efficient mechanism for the projected task. It may also be required for the public to have confidence that the aftermath of a hugely expensive disaster (such as the BSE epidemic) will be monitored effectively for as long as necessary.

 

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