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NINETY FIRST MEETING OF THE SPONGIFORM
ENCEPHALOPATHY ADVISORY COMMITTEE
The Spongiform Encephalopathy Advisory Committee held its 91st
meeting in London on 24th February 2006.
CURRENT ISSUES
SEAC was informed about the following issues:
• The Chair had received a positive response from the Chief
Medical Officer on the recommendations made in the SEAC
Epidemiology Subgroup statement on the vCJD epidemic1
and subsequent SEAC statement2. SEAC recommended
that better data on the prevalence, age and genotype
distribution, based on population studies, are required with
some urgency. This data could be obtained through testing
tissues collected from autopsies. The Department of Health
will convene an expert group to consider ethical, practical
and legal issues to take the recommendations forward.
• SEAC responded to a consultation from the European
Commission. This requested comments on the opinion of
the Scientific Committee on Emerging and Newly Identified
Health Risks on the safety of human-derived products with
regard to vCJD.
• A third case of vCJD transmission associated with blood
transfusion was announced by the Health Protection Agency
(HPA) on 9th February 2006. The recipient developed
symptoms of vCJD about 8 years after receiving a blood
transfusion from a donor, who developed symptoms of vCJD
1 http://www.seac.gov.uk/statements/state260106subgroup.htm
2 http://www.seac.gov.uk/statements/state260106.htm
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about 20 months later. SEAC was informed about the HPA
notification exercise, follow up arrangements, and further
actions relating to the remainder of the exposed group of 26
individuals. Members agreed that the case indicates that
there is significant risk of transmission of vCJD by blood
transfusion. A paper on the case is being prepared by the
Transfusion Medicine Epidemiology Review.
• Interviews had taken place for two new members for SEAC,
submissions to Ministers are in preparation.
BSE UPDATE
SEAC was presented with figures showing the annual number of
BSE cases in cattle in Great Britain (GB) since the 1980s and the
reductions in the number of cases after the introduction of control
measures. Members noted data on BSE cases reported in other
countries. In GB, the BSE epidemic peaked in 1992, with over 36
000 cases confirmed, and thereafter the number of cases declined
considerably. There have only been 124 cases confirmed in
animals born after the introduction of the reinforced ban in 1996.
Overall the GB epidemic is in steep decline with only 203 cases
confirmed in 2005.
MEDICAL IMPLANTS CONTAINING BOVINE MATERIAL
SEAC considered the risk to human health from medical implants
that include bovine material sourced from the USA. This material
was used for a wide range of medical devices, some of which are
life saving and for which there are no alternative products.
SEAC considered that the source of the animal was crucial to
manage the risk. The committee suggested that other
precautionary steps be taken where practicable, such as using
material from young animals, sourcing material from countries with
good surveillance procedures and a low prevalence of disease.
SEAC noted the lack of clarity in the regulations, which did not give
an indication of what level of risk is acceptable, and the British
Standards Institution committee scheme, which serves to assist
judgments of acceptability by determining whether the BSE risk
from a medical device utilising bovine material has been
minimised. The committee considered that a single risk
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assessment model would not be appropriate due to the variety of
devices and risk control options that are involved and the varying
degrees of risk. A risk assessment should be developed for each
specific medical device.
METHODS TO EVALUATE THE EFFICACY OF PRION
REDUCTION FILTERS
SEAC welcomed the opportunity to comment on experimental
models to evaluate prion reduction methodologies that were
developed to reduce the potential for vCJD transmission via blood
transfusion.
SEAC considered that it was important to replicate the
experiments that the companies had done to test the efficacy and
reproducibility of the filters. The committee suggested that the use
of an additional rodent strain and three different forms of inoculum
of TSE agent as the spiking material was important. This may
indicate differences in the efficacy of filters against different strains
or TSE agent. It is critical to include the BSE agent in these
studies.
SEAC considered that experiments that tested the removal of
endogenous infectivity were important and that it was crucial to try
and get a model that was as close as possible to the human
situation. The committee noted that knowledge of the prevalence
of vCJD in the population was important to the risk management
issue of implementation of prion reduction filters.
SEAC SHEEP SUBGROUP REPORT
Since the introduction of an ELISA rapid test for active surveillance
in 2002, around 100 cases of what is called atypical scrapie have
been detected in the UK. The SEAC Sheep Subgroup met on 24th
January 2006 to consider emerging scientific developments on
atypical scrapie and possible implications for the National Scrapie
Plan (NSP) and human and animal health. In its position
statement, the Sheep Subgroup concluded that the new scientific
data and identification of atypical scrapie, while of concern, do not
justify immediate changes to the NSP. Nevertheless, the
Subgroup strongly recommended that the NSP should be kept
under continuous review as new findings emerge. SEAC
concurred with this view.
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The Subgroup concluded that there is currently insufficient data to
make any conclusions about the risk to human health from the
finding of atypical scrapie in UK and European small ruminant
flocks. However, as transmission to humans is theoretically
possible, the Subgroup stressed the importance of research on
transmission of atypical scrapie in transgenic mice expressing the
human prion protein gene to inform on this issue.
SEAC agreed with the Sheep Subgroup’s conclusions and
recommendations and endorsed its position statement. The
statement can be accessed at:
http://www.seac.gov.uk/pdf/positionstatement-sheep-subgroup.pdf
USE OF LIVESTOCK AND CROPS FROM DRAYTON FARM
Defra and FSA asked SEAC to review the arrangements for
disposal of manure, crops and livestock from an experimental
farm. BSE research projects in cattle have been ongoing here
since 1998 and are nearing completion. The TSE projects in
sheep have been ongoing since 2002. SEAC previously advised
that waste from orally-challenged animals should be incinerated for
the first 28 days, thereafter the excreta should be composted for a
year and then could be used to fertilise arable land. The crops
grown subsequently could in principle be used for both human
food and animal feed.
All excreta from the orally and intracerebrally inoculated cattle
were incinerated for the first 28 days after inoculation. A 12 month
composting period was introduced for manure from the BSE
challenged animals. However, only short rotation willow coppices
were planted on the land onto which the composted manure from
the BSE challenged animals was applied.
SEAC considered that, as there is no evidence that BSE is
transmitted through environmental sources, healthy animals could
be housed in the disinfected buildings which previously housed
cattle experimentally infected with BSE. These animals could be
used for commercial slaughter or for other purposes. The current
animal tracing system will monitor the movements of these animals
in the future. There is currently no evidence that the crops
subsequently grown on the land which received composted
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excreta from BSE challenged animals pose a significant infectivity
risk to humans or animals.
DENTISTRY AND vCJD
SEAC considered the findings and implications of a preliminary
risk assessment of potential vCJD transmission via endodontic
procedures. The committee was updated with preliminary data to
assess the oral cavity as a potential route of transmission of vCJD
infectivity. This item was discussed in the reserved business
session as there was consideration of unpublished research.
SEAC considered that further data was required on the infectivity
of oral tissues and the prevalence of vCJD in the population.
However, in the absence of this information, and as there is a
theoretical risk of transmission of vCJD via endodontic procedures,
the committee suggested that the use of single use instruments for
such procedures should be seriously considered.
http://www.seac.gov.uk/summaries/seac91_summary.pdf
6 March 2006 - The final minutes (94 KB) of the 90th SEAC
meeting held on 24th November 2005 have now been published.
http://www.seac.gov.uk/minutes/final90.pdf
TSS