Public summary of the meeting on
29th September 2000

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The Spongiform Encephalopathy Advisory Committee (SEAC) met at the offices of the Ministry of Agriculture, Fisheries and Food (MAFF), Whitehall Place West, London on 29 September 2000.

 Review of BSE controls

 Sir John Krebs updated the Committee on the progress of the Food Standards Agency's review of BSE controls.

 A draft report of the review had been discussed at the last stakeholders meeting on 14 September where there had been a good degree of agreement and general support for the draft. It would be further discussed at a public meeting in York on 9 October, at which SEAC Members would be welcome. The Committee raised a few technical points in discussion of the draft. Sir John reported that a revised draft report taking account of comments made by SEAC and other interested parties would be prepared in time for discussion at a final stakeholders meeting on 2 November. The report, after taking account of recommendations from the Philips Inquiry, would then be submitted to the Agency's Board for approval before being published and submitted to Health and Agriculture Ministers.

Consideration of recent Scientific Publications

Species Barrier Independent Prion Replication In Apparently Resistant Species

 Members considered recent published work from Professor Collinge's group demonstrating that asymptomatic mice that were not thought to be susceptible to TSE infection were still able to replicate prion protein to high levels and could transmit disease to other mice (ref1). SEAC noted the implications of the work in regard to the possibility that prion disease may exist in a sub-clinical form. Members noted that existing UK control measures with respect to the safety of beef products took account of the possibility that animals with no clinical signs may be incubating the disease. They agreed that the experiment did not raise immediate public or animal health concerns. However the Committee was concerned about the possible implications of subclinical infection in countries where BSE was present and where less stringent control measures were in place than in the UK. The Committee also recommended that further research on pigs and poultry should be undertaken to extend earlier findings indicating that these species did not harbour TSE infectivity when orally exposed.

Transmission of BSE By Blood Transfusion In Sheep

 SEAC considered the recent publication of ongoing work at the Institute of Animal Health examining transmission of experimental BSE between sheep through blood transfusion (ref 2). Members noted that the experiment was at an early stage and positive transmission was limited to a single sheep. Therefore further work would be required before the result could be fully interpreted. However, the Committee considered whether, in the light of this initial finding, further measures to protect human or animal health were needed.

 On the question of the safety of human blood and blood products, the Committee concluded that the measures the Committee had previously advised should be taken on a precautionary basis had to a considerable extent anticipated such a finding and the previous recommendation with respect to leucodepletion remained appropriate. The Committee recommended no additional control measures at this time, but noted that it would be important to ascertain the extent to which leucodepletion reduced or eliminated infectivity in the blood of sheep experimentally infected with BSE.

 In relation to food safety, the Committee concluded that the finding reported did not present grounds for recommending any changes to the current controls. The Committee considered that the finding did not change their view on bovine products, in the absence of any indication of infectivity in bovine blood, but grounds for additional caution would arise if BSE were ever to be found in commercial sheep.

 In relation to animal health, SEAC reviewed the use of dried mammalian blood in animal feed, which is currently permitted under EU legislation. SEAC agreed that there was no evidence to suggest the presence of BSE infectivity in cattle blood. Additionally, the Committee was informed that blood products are rarely used in farm animal feed in the UK and any bovine blood for animal feed would be sourced from animals under 30 months of age. Therefore, SEAC concluded that, although within species recycling should be discouraged, in the case of dried bovine blood, the risks were extremely small and hence there was no compelling need to change previous advice.

 Also, because source material for gelatin and tallow was tightly controlled and subject to processing that would reduce any infectivity present, Members were also content for gelatin and tallow to remain exempt from the current feed ban. However, Members considered there was a theoretical possibility that if blood meal derived from a sheep infected with scrapie were included in a sheep ration, this could present a risk to animal health. If so, it may theoretically compromise current efforts to eradicate scrapie from the national flock. SEAC asked that this potential risk and its implications be considered within the context of the national scrapie eradication plan.

DH R&D and vCJD update

 The Committee conducted its regular review of research findings and epidemiological information on vCJD. The Committee was informed that the total number of cases of confirmed and probable cases of vCJD now stood at 84, of which 7 were still alive.

 The Committee was informed that the investigation into the apparent cluster of vCJD cases in Leicestershire was well underway, and likely to report its findings by the end of the year.

Risk assessment for surgical instruments

 The Committee returned to the question of the draft report assessing the theoretical risk of person to person transmission of vCJD from surgical instruments. This was to follow up a decision at its meeting in May 2000 to endorse the methodology but to remit some of the draft report's key assumptions to a Sub-Group for further consideration. The Committee endorsed revisions to the draft report which took account of conclusions since reached by the Sub-Group. In particular they endorsed the input value ranges to be used within the modelling on which the report would be based. These value ranges reflected estimates of relative levels of pre-clinical infectivity theoretically possible within various body tissues.

 In the light of the revised draft report, the Committee revisited its earlier statements on steps it would recommend to reduce the risk of person-to-person transmission. The Committee reiterated its earlier view that rigorous implementation of washing, decontamination and general hygiene procedures were key steps in reducing any risk, and stressed the importance of ensuring that such steps were fully implemented within the health care setting. It further concluded that although the theoretical risk could depend on a number of factors, it was likely to be greatest from operations involving central nervous system and posterior ophthalmic tissue, followed by lymphoid and anterior ophthalmic tissue. Where discrete surgical procedures can be identified as suitable for single use instruments, for example tonsillectomy, and provided patient safety would not be compromised, the Committee considered that such use should be considered wherever practicable.

MAFF R&D update

 The Committee conducted its regular review of research findings and epidemiological information on BSE. SEAC noted that in ongoing experiments to examine the pathogenesis of experimental BSE in sheep, Suffolk sheep of susceptible genotype had shown evidence of infectivity in their tissues from 10 months post inoculation. However, encouragingly, no tissues from resistant or semi-resistant sheep had yet been found to be positive.

 The Committee briefly considered the cases of suspected BSE reportedly found in sheep in the US. Members noted that an EU mission had recently concluded that on the basis of current information, there was no reason to suspect that the sheep were infected with BSE.

 The Committee noted that a correction needed to be made to the figures presented in Table 1 at the end of the November 1999 SEAC Public Summary on the predicted BSE case incidence, including those cases in animals born after mid 1996. The figures presented in the table did not take account of the estimated effects of the offspring and selective culls. This did not have a significant impact on the majority of the data presented in the table, however, for column 3 - 'Predicted cases in animals born after mid 1996' - the predicted numbers of cases for 1999-2001 should be reduced to the following:

 

 

All data assume 10% maternal transmission occurs where calves are born to infected dams within 6 months of clinical onset. A case of BSE was confirmed on 27 June 2000 in a Holstein/Friesian dairy cow born on 25 August 1996. To date this is the only recorded case of BSE in a cow born after 1 August 1996, the date when further measures to improve feed security were considered to be fully effective (the actual number of cases is therefore below the predicted level). Members briefly reviewed the recent report on investigations on the likely route of exposure in this case, which concluded that no definite transmission route could be implicated.

Sheep and cattle surveillance

 A SEAC sub-group had been asked to consider surveillance strategies to better define the incidence of scrapie in the UK sheep flock. Members concurred with the sub-group's initial recommendations, which were to repeat an anonymous postal survey of farmers to establish how reproducable previous results were regarding scrapie incidence. SEAC also agreed that there should be a pilot study to identify the costs and practical constraints of performing a large-scale longitudinal study to establish a baseline for the incidence of scrapie. Finally SEAC underlined the importance of carrying out an abattoir survey to monitor changes in the prevalence of scrapie in sheep going into slaughterhouses. Members felt that this had the highest priority.

 SEAC also considered options for an abattoir survey of cattle brains from animals born after 1 August 1996 to check the effectiveness of the feed ban. Members recommended that a survey should begin in August 2001. Timing the survey to start then would ensure that the samples to be analysed would come from 5 year old cattle, thus coinciding with the peak incidence of clinical BSE. It would therefore be most likely to pick up animals developing BSE, should there be any.

Dicalcium Phosphate

 Members agreed that imported bovine bones and bones from UK cattle under thirty months of age could be used to produce dicalcium phosphate for poultry feed. However, because of concerns about intra-species recycling, Members felt that this practice could only be allowed if it could be assured that the material would not be included in feed for any other livestock. If this could not be guaranteed then it should not be used.

Risk Assessment on the use of small incinerators to burn SRM

 Members were asked to consider the terms of reference for an independent study on the potential risks to human health from small incinerators burning SRM. Such incinerators are commonly found at hunt kennels and knackers yards and typically handle small numbers of casualty animals and fallen stock. Members agreed the terms of reference, but considered that the scope of the study should be widened to include the incineration of sheep SRM and to assess potential risks to animal as well as human health.

Committee procedures - Openness

 SEAC agreed to publish future agendas from each meeting prior to the release of the public summary and the associated press briefing. (A copy of the agenda for this meeting is attached at Annex A.) Members also signalled their intention to hold an open meeting sometime next year.

 Members agreed to discuss any implications for the working of the Committee arising from the BSE Inquiry report at their next meeting in November

Updates on agenda items from previous meetings and other matters arising

 Members noted that: 

1. the consultation document on phase 1 of the national scrapie plan for Great Britain had been published. The closing date for comments is 31 October 2000;
2. that the British Dental Association has advised dentists to take account of the Committee's advice stressing the importance of thorough decontamination procedures on dental instruments;
3. invitations to tender for the risk assessment work in sheep had been issued to six prospective contractors. Proposals were due to be returned in the next few days.

The next meeting of the Committee will be held on 28 November 2000. The press briefing for the November meeting will be held on 19th December when the public summary of the Committee's discussions at that meeting will be published.

References

1- Hill et al 2000, Species-barrier-independent prion replication in apparently resistant species. Proceedings of the National Academy of Sciences Vol. 97, N18, 10248-10253

2- Houston et al 2000, Transmission of BSE by blood transfusion in sheep. The Lancet Vol. 356, 999-1000

SEAC
September 2000

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