Public summary of meeting on
27th June 2001

The Spongiform Encephalopathy Advisory Committee (SEAC) met in London on 27 June 2001.

Report of the working group on disposal of carcasses of cattle culled for foot and mouth disease (FMD) control

The Committee discussed the conclusions of the SEAC working group meeting on 24 May which met to consider the following FMD disposal issues:

  • the risks from carcasses of cattle aged over 5 years buried prior to advice from SEAC, and revised advice from the Environment Agency (EA), given on 26 March.
  • disposal routes for ash from cattle burned in pyres.
  • BSE risks from transportation of cattle carcasses (culled for FMD control) in containers which might subsequently be used for transportation of food.

A separate public summary setting out the detailed conclusions of this group was published in May.

The Environment Agency updated the Committee on progress made to date on the recommendations made at the meeting on 24 May. They were progressing as quickly as possible with risk assessments of individual sites and, on the basis of SEAC's advice, were comparing the risks of exhuming material against the risks of leaving it in situ. Where cattle over 5 years old had been buried, further risk assessments would need to be undertaken when farms were restocked to assess any BSE risks to animal health. Analysis of ash from cattle burned in pyres indicated that the assumption of 90% destruction of infectivity, made in the DNV risk assessment, was reasonable. Currently, all cattle aged over 5 years culled as a result of the FMD outbreak were being disposed of by rendering.

The Committee endorsed the conclusion of the working group and agreed that a detailed note of the group's discussions should also be published.

BSE case born in 1997

The Committee considered a recently confirmed case of BSE in an animal born in May 1997, 10 months after 01 August 1996, the date when further measures to improve feed security were considered to be fully effective. This was the third such case in the UK. It had been predicted that a small number of BSE cases would be born after the implementation of further measures arising through the risk of maternal transmission of BSE (to calves born close to the onset of BSE in the dam (mother)). The case was of particular interest and concern because the animal believed to be the case's dam was still alive with no signs of BSE. The animal with BSE did not pose a risk to public health because it was aged 48 months and so was not eligible to enter the human food chain because of the over thirty month rule.

The Committee noted that, as for any BSE cases born after 01 August 1996, an investigation was currently underway to examine possible routes by which the animal may have been exposed to the BSE agent. The report from this investigation would be available in time for SEAC's next meeting in September and members agreed to revisit the issue then.

Members noted that it was during the tail-end of the epidemic, when the major route of BSE contamination from feed had been removed, that unspecified, rare alternative routes of transmission might be seen. Members acknowledged that it would be difficult to come to definitive conclusions in regard to possible alternative routes of exposure aside from feed contamination or maternal transmission. This would be particularly true of environmental sources because of the difficulty of detecting the agent, if present. However, the Committee agreed that alternative routes of transmission should be examined where practicable.

The Committee considered options to investigate the surviving relatives of this BSE case, including a single offspring of the animal currently alive on farm. Under current offspring cull legislation, all offspring should be destroyed. However, Members agreed that this animal should be preserved for further investigation on a suitable experimental farm. Members also agreed that the dam and siblings of the BSE infected animal should be closely monitored and a strategy devised to maximise the information gained from these animals.

Members agreed that, if possible, brain material from this case should be strain typed to determine if the BSE showed any unusual characteristics. More generally, Members expressed concern that the samples currently being taken from suspected cases of BSE in animals born after August 1996 may not be collected in a way that would enable strain typing to be done and urged that suitable material should be collected from these animals. The Committee also considered that a wider range of tissues from such animals, when born after August 1996, should be collected for examination in future. This would allow widespread pathology and the distribution of the prion protein that causes BSE to be examined and unusual strain variants to be detected. It was noted that this may have substantial resource implications as large numbers of suspect cases are identified, the vast majority of which are subsequently diagnosed as negative, hence there would be a need for suitable facilities to store large quantities of tissues from these suspect animals until diagnosis was complete. However the issue would be investigated further for the next meeting.

In summary, SEAC was broadly content with the plan to investigate the case.

  • The Committee strongly recommended that every effort should be made to ensure that the calf of the BSE case was not slaughtered as part of the offspring cull as it represented a potentially valuable scientific opportunity to study the disease.
  • The Committee also recommended that a protocol on what should happen to the dam should be produced, by a group with expertise in tissue sampling, collection and diagnostic testing methodology.
  • Finally, the Committee recommended that changes should be made with respect to the collection of samples such that if BSE was identified in animals born after August 1996 a greater number of tissues would be retained. These should be collected and stored in a form that would allow a wider range of scientific investigations to be carried out.

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BSE epidemiology in Northern Ireland.

Casualty animals

At their meeting in February 2001, Members requested further information on results from a survey of casualty animals (animals injured but alive when entered into the survey) over thirty months of age in Northern Ireland which indicated evidence of BSE infection in 54 cattle of the 2546 sampled using the Enfer diagnostic test (2.12%). The Committee confirmed that the results appeared to be at some variance with the low incidence of reported clinical BSE in Northern Ireland. However it was noted that the samples were taken from older cattle that were registered as casualty animals, and so were from a group of animals where BSE incidence was likely to be comparatively high. All animals were over thirty months of age so would not have entered the food chain.

DEFRA reported that various active surveillance exercises in the UK continued to be delayed as a result of the FMD epidemic. A small number of samples had been analysed as part of the GB fallen stock (animals found dead on farm) survey and approximately 2% had shown evidence of BSE infection. Although this was similar to the level of BSE seen in the Northern Ireland survey, the GB survey was not at a stage where results could be assessed. More generally, comparing results from different surveys was difficult as it was unlikely that the sample populations were uniform. For example the UK survey examined fallen stock rather than casualty animals.

The Committee then moved on to a general discussion on the validity of the diagnostic tests being used for surveillance in surveys in the EU. It was known that the tests were limited in their ability to detect the presence of prion protein that is taken as marker for infection. They could only detect a positive case a few months before clinical disease became apparent, meaning that pre-clinical cases were probably being missed, but the exact timing of when the test could detect prion protein prior to clinical onset was not known. This meant that the tests were likely to be underestimating the prevalence of infection. However, the size of the underestimate was not known and the Committee considered there was a need to calibrate the tests against tissues from known stages of the disease to overcome this problem. Members emphasised the importance of work to establish when in the pre-clinical phase diagnostic tests were able to detect prion protein and thereby, infection. The Committee stated that their preference was to validate current tests using bovine material collected throughout the incubation period. However, it was recognised that there was a paucity of suitable material currently available to test in this way. A specific research project was underway to harvest tissue collected throughout the incubation period of cattle infected with BSE. However this was not complete and hence current stocks of such tissue were very scarce and the tissues very valuable. They were needed for a wide range of experiments and demand exceeded supply. Members requested that an audit of the tissue and its proposed use should be undertaken for consideration at a future meeting.

Case of a cow born after August 1996 in Northern Ireland

Members were updated on investigations into the case of an animal born after 01 August 1996 in Northern Ireland (detected in the survey of casualty animals). Although the date of birth was recorded as 10 September 1996, there was some doubt about the reliability of this information. The investigations did not identify the likely route of exposure.

Royal Society and the Academy of Medical Sciences Paper on TSEs

The recently issued Royal Society and the Academy of Medical Sciences statement on TSEs recommended that urgent consideration be given to the possibility of cross infection in abattoirs which handle both slaughter for food and culling under the Over Thirty Months Scheme (OTMS). In the light of this recommendation, the FSA sought the Committee's advice on the risk of contamination of meat in such abattoirs and whether the existing guidance on decontamination of these premises after OTMS processing was adequate. The Committee concluded that use of abattoirs for both food animals and the OTMS was likely to give rise to an additional risk. The magnitude of that risk was unknown but was probably low if the recommended cleaning and decontamination procedures were followed. The Committee advised nevertheless that, on a precautionary basis, it would be preferred that abattoirs, while contracted to carry out OTMS work, did not handle any slaughter for human consumption.

Review of spreading of slaughterhouse material on fields

Following a request from their meeting on 25 April 2001, SEAC considered a paper reviewing what animal materials, including slaughterhouse and rendering plant materials, were currently spread on agricultural land. The paper indicated that milk, blood, gut content, slurry, non-mammalian rendered MBM, and treated rendering condensate can currently legally be spread on agricultural land. The Committee were asked whether they wished to look at any of these areas in greater detail at a future meeting. SEAC considered rendering condensate in detail at their November 2000 meeting and asked to consider in more detail at a future meeting issues related to faeces and sewage sludge disposal, from both cattle and humans, with respect to the potential presence of both BSE and vCJD infectivity.

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Intra-species Recycling: review of what practices exist/remain within the livestock industry

At the meeting in April 2001, Members requested a review of what practices remain in terms of intra-species recycling within the livestock industry. The Committee were asked to identify those that they wished to look at in greater detail at a future meeting. They agreed that they would wish to look again at tallow, gelatin, hydrolysed protein, fishmeal, and eggs and egg protein.

FSA review of BSE controls: taking forward the recommendation on the OTM rule

Following the recommendation in the Review that the OTM rule should be further reviewed, starting summer 2001, the FSA invited the Committee to note its initial plans to implement that recommendation and invited comments on the factors it intended to take into account. The Committee agreed that information from the BSE surveillance programmes to be carried out by the UK agriculture departments including the testing for BSE of animals born between August 1996 and July 1997 would be crucial to the review

Lenses and ophthalmic devices touching the surface of the eye

The Committee revisited the advice it issued following the meetings in July and September 1999 on the re-use of contact lenses and ophthalmic devices that touched the eye. They noted results of as yet unpublished research findings(1) (subsequently published- see reference 1) where abnormal prion protein had not been detected in the front of an eye from a vCJD patient. When taken together with results from further as yet unpublished research(1) ,this suggested that any abnormal prion protein present in these segments of the eye would be at a lower level than previously assumed, and probably below that present in lymphoreticular tissue in vCJD patients. At the same time the committee considered that the likely levels present could not be precisely quantified because of insensitivities in the assay used. They also noted results of research (see references 2-6) demonstrating that a solution containing 20,000 parts per million (ppm) of available chlorine of sodium hypochlorite is very effective in reducing TSE infectivity. Some members had doubts about whether such reductions would be as effective in practice with respect to infectious material that might be adhering to the surfaces of lenses and ophthalmic devices. This was an aspect on which further research was needed.

The Committee considered that wherever practicable a single use approach should be followed for lenses and devices coming into contact with the front of the eye. Evidence was presented to the meeting by the optical profession that single use was impracticable for some devices, including rigid complex diagnostic lenses, tonometers, and other highly specialised equipment. The committee considered that in such circumstances it would be important to apply best decontamination procedures, including, as appropriate, the use of a solution containing 20,000 ppm of available chlorine of sodium hypochlorite.

Scientific references relating to this item

  1. Wadsworth et al. (2001) Tissue distribution of protease resistant prion protein in vCJD using a highly sensitive immuno-blot assay. Lancet 358, 171-180.

  2. Taylor DM. Inactivation of Transmissible Degenerative Encephalopathy Agents: A Review. The Veterinary Journal 2000;159:10-17 (NB p14)

  3. Taylor DM. Inactivation of prions by physical and chemical means. Journal of Hospital Infection 1999; 43 (suppl): S69-S76.

  4. Taylor DM et al. (1994) Decontamination studies with the agents of bovine spongiform encephalopathy and scrapie. Archives of Virology 139, 313-26.

  5. Brown et al. (1986) Newer data on the inactivation of scrapie virus or CJD virus in brain tissue J of Infect Dis. 153 6 1145-1148.

  6. Kimberlin et al. (1983) Disinfection studies with two strains of mouse-passaged scrapie agent. J of Neurological Sciences 59 : 355-369

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Research updates and other standing items

Variant Creutzfeldt Jakob Disease Update

The Committee was informed that the total number of definite or probable variant Creutzfeldt Jakob Disease (vCJD) cases had now risen to 102, of whom 8 were still alive.

Department of Health Research Update

The Committee received its regular update on research commissioned by the Department of Health. In particular, it noted that, following the Transmissible Spongiform Encephalopathy (TSE) Joint Funders Research Group's (which includes DEFRA, DH, FSA, MRC & BBSRC) call for proposals in March 2001 to encourage research on diagnostic tests, 55 responses had been received to date. The Committee was informed that a number of the proposals appeared promising, and a formal assessment of those which merited funding would take place in the near future.

DEFRA Research Update

The Committee conducted its regular review of research findings and epidemiological information on BSE. The Committee noted ongoing research to examine a selection of scrapie brains from UK farms; these are being tested to see if there is BSE in sheep, which could otherwise be masked by scrapie. These are long term experiments using mice and take up to two years to complete. Currently, 183 individual scrapie brains are being tested. Of these, 156 brains have reached a point when the mice would be expected to display signs characteristic of BSE, if present. No such characteristic signs have been seen.

SEAC noted that in ongoing experiments to examine the pathogenesis of experimental BSE in sheep, infectivity had been detected in the liver of genetically susceptible sheep at 16 and 22 months after challenge using mouse bioassay. The Committee also noted that the experiment to define the effect of oral doses in cattle had been terminated. Cattle had been dosed orally with BSE brain homogenate. Doses were 1g, 10g, 100g, and 3 X 100g. Other than five remaining animals in the two lower dose groups, all other animals had succumbed to clinical disease. However, the remaining five animals had been culled with no evidence of clinical signs, and no evidence of BSE pathology was seen when brains were examined at post mortem. The Committee noted therefore that a limiting dose for BSE via the oral route had not been reached, and the experiment is currently being extended using a lower dose range.

FSA Research Update

The FSA presented a paper on its TSE R&D programme summarising progress on each project during the period 01 April 2000 to 31 March 2001. The Committee noted the report.

Imports of beef and beef products

The FSA reported the latest position on imports of beef with remnants of spinal cord attached. The number of affected consignments had risen to sixteen. The FSA would be writing to the European Commission to press for a thorough investigation of the latest instance, which had been the second involving a particular German abattoir. The FSA also reported on the latest results of BSE testing in the EU and the first BSE case reported by the Czech Republic.

Committee matters

Code of Practice for Scientific Advisory Committees - Second Round of Consultation: Update

Following a request for comments from members on the Office of Science and Technology's (OST) consultation on a new Code of Practice for Scientific Advisory Committees at SEAC's April meeting, a response on behalf of the Committee had been compiled and submitted to OST.

Open meeting

Members noted that arrangements for SEAC's next meeting, part of which would be in open session, were now in place. The meeting would take place on the 18 September at the Inter-Continental Hotel, London. As previously agreed, Members would meet for an open session in the morning, followed by a closed session in the afternoon. The agenda would be set nearer the date of the meeting when there was a clearer indication of what the current issues were.

Matters arising

Vaccination of experimental animals against FMD

At their meeting in April, the Committee had recommended that urgent consideration be given to vaccinating experimental animals being used in TSE studies at research centres to protect them from the risks of being culled under FMD control measures. Following SEAC's recommendations, the possibility of introducing a vaccination program had been investigated and a risk assessment had been carried out at the Veterinary Laboratories Agency (VLA) to examine the risk to experimental animals in light of the existing containment measures. Generally the risks to experimental animals had been assessed to be low. However the Committee was informed that currently there was little scope for vaccinating these animals without compromising the long-term disease status of the country.

SEAC
26 July 2001

Note of SEAC Working Group on disposal of carcasses of cattle culled for Foot and Mouth Disease (FMD) control