From: TSS ()
Subject: 21st April 2005 (SEAC 87) and 3rd March 2005 (SEAC 86) summary plus minutes
Date: May 4, 2005 at 8:25 am PST
-------- Original Message --------
Subject: 21st April 2005 (SEAC 87) and 3rd March 2005 (SEAC 86) summary plus minutes
Date: Tue, 3 May 2005 12:17:23 -0500
From: "Terry S. Singeltary Sr."
Reply-To: Bovine Spongiform Encephalopathy
##################### Bovine Spongiform Encephalopathy #####################
EIGHTY-SEVENTH MEETING OF THE SPONGIFORM
ENCEPHALOPATHY ADVISORY COMMITTEE
The Spongiform Encephalopathy Advisory Committee held its 87th
meeting in London on 21st April 2005, when it discussed the
SEAC was updated on the following current issues:
• A request from the National Blood Transfusion Service for
SEAC advice on the use of prion reduction filters for blood.
The committee strongly recommended that such products
should be independently validated.
• The SEAC Epidemiology Subgroup would meet in May to
discuss the issues related to the predicted profile of the vCJD
epidemic identified by SEAC at its last meeting.
• A collaboration between the MRC Prion Unit and
GlaxoSmithKline to develop prion disease therapies had been
• France is to increase its surveillance of TSEs in goats.
• The recent case of probable iatrogenic CJD related to a
certain type of dura mater graft that was performed in 1987.
The committee noted that the TSE related risks associated
with this procedure were now well known and that such grafts
no longer take place in the UK.
• A number of SEAC members had looked at a submission
hypothesising that toxic alkaloids in ryegrass may have been
a contributing factor in the BSE epidemic. The members had
agreed that the evidence put forward in support of this
hypothesis was not sufficiently rigorous or compelling to
warrant a full discussion. Furthermore, the evidence that
contaminated meat and bone meal was the primary cause of
BSE epidemic remains strong.
EARLY PHASE OF vCJD INFECTION IN BLOOD
The Committee on Microbiological Safety of Blood, Tissue and
Organs (MSBTO) asked SEAC for advice on whether a scientific
distinction could be drawn between potential tissue/organ donors
that have received blood transfusions either a few days before
donation or in the more distant past, in terms of the relative load of
vCJD agent that might be present in bone, tissues or organs.
The committee noted that the current risks of blood transfusionassociated
transmission of vCJD from tissue/organ donation are
lower now than prior to the introduction of the recent, additional
precautionary safety measures to protect the blood supply, e.g.
exclusion of previously transfused blood donors.
The committee considered that a small background risk of vCJD
infection exists in the population as a whole. Therefore, a risk of
transplant associated transmission of vCJD exists from
tissue/organ donors that have not received blood transfusions.
The additional risk as a result of a donor having received a blood
transfusion at any time prior to donation is likely to be small.
The committee noted that relevant data on prion replication and
spread following transfusion were extremely limited and mostly
from animal models not directly applicable to the human situation.
However, in the first few days following a transfusion with infected
blood, significant prion replication was unlikely and, therefore,
tissue prion levels would be related to the blood supply to the
tissue in question. Highly vascularised organs such as liver, lung
and spleen were more likely to contain the agent compared with
A balance must be struck between the small increased risk of prion
transmission by transplant and the benefit to patients of receiving a
transplant, especially where tissues/organs are scarce. The
committee noted that screening of cadaveric donors for the
presence of abnormal prions prior to transplantation, washing
tissues/organs to remove blood before their use, and avoiding the
pooling of tissues may reduce transplant associated transmission
REPORT FROM THE AD HOC EPIDEMIOLOGY SUBGROUP
ON UK BARB CASES
In March 2004, an ad hoc SEAC Epidemiology Subgroup on UK
BARB cases was convened to advise on the design of a case
control study to identify possible causes of BSE cases born after
the 1996 reinforced feed ban (BARB cases). The Subgroup was
reconvened in April 2005 to discuss preliminary results from the
study. Professor Noel Gill, chair of the Subgroup, reported the
outcome of the Subgroup’s considerations to SEAC.
SEAC endorsed the Subgroup’s recommendations for further
analysis of the results using different criteria to define the controls
used in the study, to continue the study using a more sophisticated
group of controls, and for prospective evaluation of animal feed
use and supply routes and the potential for cross-contamination of
feeds. These issues will be considered by SEAC at the June
meeting when Professor Hill, who has been commissioned by
Defra, reports on his investigation of the cause of BARB cases.
SEAC considered it important to use new more sophisticated
molecular approaches to characterise BARB cases and gather as
much information as possible on cases as they arise.
USE OF CATEGORY 3 ANIMAL BY-PRODUCTS IN
Defra asked SEAC to consider a release assessment to estimate
TSE-related infectivity levels associated with the use of rendered
category 3 animal by-products in fertiliser for non-pasture land.
The committee was generally content with the approach used and
assumptions made in the assessment. It was recommended that
further consideration is given to the possibility that potentially
infected fertiliser is not evenly distributed. It was noted that little is
known about the persistence of TSE agents in soil. Thus, intraspecies
recycling of mammalian protein in fertiliser was possible.
Although, the risks of transmission of TSEs via this route may be
very small, a watching brief should be maintained.
VERTEBRAL COLUMN: AGE AT WHICH SPECIFIED RISK
FSA asked SEAC to review an assessment of the possible UK
exposure to BSE associated with vertebral column from cattle
aged under 12 or under 30 months.
SEAC was content with the approach used and assumptions made
in the risk assessment. The committee noted that some
uncertainties remained with regard to the extent of the species
barrier between cattle and humans although these uncertainties do
not significantly affect the overall conclusions. Exposures had
been calculated for the UK population, without considering whether
a small subgroup within the population might consume most of the
UK beef on the bone. Nevertheless, although exposure would be
higher in consumers of beef on the bone than for the general
population assumed in the study, it was considered that the
increased risk to this population group would still be very small.
The committee concluded that the difference in the BSE-related
risk from vertebral column as specified risk material from cattle of
12 and 30 months of age was negligible.
EIGHTY-SIXTH MEETING OF THE SPONGIFORM
ENCEPHALOPATHY ADVISORY COMMITTEE
The Spongiform Encephalopathy Advisory Committee held its 86th
meeting in London on 3rd March 2005, when it discussed the
PROFILE OF THE vCJD EPIDEMIC
Projections of the profile of the vCJD epidemic based on data from
clinical vCJD cases to date have suggested the number of
additional cases may be relatively small. However, recent
experimental and epidemiological findings have suggested that the
nature of the epidemic might be more complex and that there may
be individuals who are carriers of infectivity but who do not
necessarily develop clinical disease. Furthermore, potential
human to human infection via medical procedures (e.g. use of
contaminated surgical instruments or blood) might influence the
profile of the epidemic such that, if appropriate intervention is not
taken, a self-sustaining epidemic could arise.
SEAC conducted an initial consideration of the new information
and received papers and presentations from a number of leading
experts. The committee recognised that a survey of abnormal
prion protein in human tonsil and appendix samples suggests that
the prevalence of BSE infection in humans might be somewhat
higher than predicted from the clinical case data alone. Research
using mice carrying different forms of the human prion protein
gene indicates that the susceptibility to, and characteristics of,
BSE infection such as incubation period, may be influenced by the
form of prion protein gene individuals carry. Information about
Kuru, a human prion disease of cannibals in Papua New Guinea,
supports this suggestion. New epidemiological evidence suggests
that younger people might be relatively more susceptible to
infection. However, the age of greatest susceptibility is unclear.
SEAC agreed that further epidemiological analysis and modelling
work is required to comprehensively reassess the nature and
future profile of the vCJD epidemic. The committee tasked the
SEAC Epidemiology Subgroup to conduct this assessment taking
into account the new research and the possibility of human to
human infection. The subgroup was also asked to identify critical
factors that could influence the nature of the epidemic, and to
consider the likelihood of a self-sustaining epidemic and key
interventions which might prevent this. The subgroup will report its
considerations to SEAC at a future meeting.
Defra recently commissioned Professor William Hill, as an
independent advisor, to consider possible causes of BSE cases
born after the 1996 UK reinforced animal feed ban (known as
BARB cases). Professor Hill asked SEAC to identify issues that
should be considered as part of his report. The committee
identified a number of key areas for investigation. These included
assessment of data on BSE cases in other countries, possible
genetic relationships between BARB cases, and possible
environmental causes such as the mineral content of grazing
pastures or the presence of toxic alkaloids in feed. SEAC will
consider Professor Hill’s completed report at a future meeting.
BSE IN GOATS
Following the recent finding of possible BSE in a UK goat which
died in 1990, Defra and FSA asked SEAC for its view on further
research and the current level of risk in relation to consumption of
UK goat meat or dairy products. The committee was presented
with experimental evidence about the case.
SEAC agreed that the evidence suggested the goat had indeed
been infected with BSE. However, it was noted that the goat had
been born around the time of the peak of the BSE epidemic and
before the feed bans had been introduced. Therefore, it was likely
to have been exposed to feed highly contaminated with the BSE
agent. It was noted that BSE had not been found in the offspring
of this goat or in other goats from the farm. It therefore appeared
to be an isolated case.
SEAC concluded that there is no evidence for BSE in the current
UK goat herd, and as goats are no longer exposed to
contaminated feed the likelihood of goats in the current flock being
infected with BSE is low. However, SEAC noted that surveillance
of TSEs in goats is very limited and welcomed plans to increase
surveillance and to examine other historical samples of goats that
may be available, which should enhance confidence in this
The committee concluded that, on the basis of current evidence,
and the control measures currently in place aimed at reducing
potential risk, it is reasonable for the FSA to continue not to advise
against the consumption of goat meat or diary products. However,
as surveillance is very limited, and the distribution of BSE
infectivity in goats is not well understood, a potential risk of BSE
from goat meat and dairy products cannot be entirely excluded.
FINDINGS OF HEIKENWALDER ET AL (2005)
A recent paper (Heikenwalder et al., published 2005 in Science)
reported that in mouse models, chronic inflammation altered the
tissue distribution of scrapie prions and infectivity. In these mice,
scrapie prions and infectivity had been detected in tissues not
normally infective. The FSA asked SEAC to consider the
implications of the findings for specified risk material (SRM)
controls which prevent animal tissues known to be potentially
infective reaching the human food chain.
The committee agreed the findings were very interesting. It was
noted that the immune system of the mice had been genetically
modified resulting in very specific and severe forms of
inflammation which may not reflect conditions that normally apply
on the farm. Thus, it would be premature to conclude that such
inflammation altered the effectiveness of SRM controls. Further
work would be required to investigate more fully the influence of
inflammation on prion disease and infectivity.
The committee noted that inspections of animals at abattoirs
restricted the entry of unhealthy animals into the food chain. Thus,
animals with severe inflammation should normally be excluded
from the food chain. Nevertheless, the committee agreed that to
minimise potential risk the Meat Hygiene Service should continue
to be particularly vigilant in this area.
SPONGIFORM ENCEPHALOPATHY ADVISORY COMMITTEE
Minutes of the open session of the 86th meeting held on 3rd March
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