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From: TSS (216-119-136-146.ipset16.wt.net)
Subject: THE SPONGIFORM ENCEPHALOPATHY ADVISORY COMMITTEE OPEN MEETING 11th February 2003
Date: February 11, 2003 at 11:03 am PST
In Reply to: U.K. GOV. WILL ANNOUNCE A DEFINITE LINK BETWEEN SPORADIC CJD AND BSE aka MAD COW DISEASE !!! posted by TSS on February 10, 2003 at 4:38 pm:
PUBLIC ANNOUNCEMENT
THE SPONGIFORM ENCEPHALOPATHY ADVISORY COMMITTEE
OPEN MEETING
The February meeting of the Spongiform Encephalopathy Advisory Committee (SEAC) will be
open to the public. This will take place on the 11th February 2003 at the DTI Conference Centre,
Victoria Street, London.
SEAC’s remit is to provide scientifically based advice to the Department for Environment Food
and Rural Affairs, the Department of Health, the Food Standards Agency, and the devolved
administrations on matters relating to spongiform encephalopathies, in particular BSE and variant
CJD. The meeting will enable interested groups and individuals to observe and gain an insight in
the workings of the Committee and to increase the public’s understanding of TSEs.
The agenda and the papers for the February meeting will be finalised shortly and will be available
on the SEAC website one week prior to the meeting.
Admittance will be by registration only with places issued on a ‘first come, first served’ basis.
Please contact the SEAC Secretariat at the address below by no later than 3rd February 2003
if you wish to attend the February meeting.
Further meetings have been confirmed for 30th April 2003 and 24th June 2003.
A similar notice will be placed on the website nearer the times of these meetings.
SEAC Secretariat
Area 607, 1A Page Street,
London. SW1P 4PQ
Email: SEACsecretariat@seac.gsi.gov.uk http://www.defra.gov.uk/ Agenda
77th meeting on Tuesday 11th February 2003.
Department of Trade and Industry Conference Centre
1 Victoria Street, London.
SW1H 0ET. Item No Time Item Presenter Paper No. 1 10:15 Chairman's introduction Professor P.Smith 2 10:25 Approval of draft minutes from 14 November SEAC meeting (SEAC 76) Professor P.Smith 77/1(pdf) 3 10:35 Report from the 11 December sheep sub-group meeting. Professor P.Smith 77/2 # 4 11:00 BSE prions propagate as either vCJD like or sCJD like prion strains in transgenic mice, expressing human prion protein (EMBO Journal). Professor P.Smith
77/3(pdf) 5 11:30 BSE offspring cull Dr J.Bailey (DEFRA)
77/4(pdf) 6 12:00 vCJD update Professor J.Ironside
(Deputy Chairman) 7 12:20 BSE in the UK and other Member States. Mr P.Soul (DEFRA) 77/5 (pdf) 8 12:40 Departmental Research Updates DH
DEFRA Dr.J.Stephenson (DH)
Dr.P.Barrowman(DEFRA) 77/6(pdf) 9 13:00 A.O.B
# This paper will be circulated to SEAC members only. It will then be released on this website following ratification by the committee. © SEAC 2003
1
SEAC No: 77/3
BSE PRIONS PROPAGATE AS EITHER VARIANT CJD-LIKE OR
SPORADIC CJD-LIKE PRION STRAINS IN TRANSGENIC MICE
EXPRESSING HUMAN PRION PROTEIN. ASANTE et al. (2002)
EMBO 21, (23) 6358-66
Issue
1. A research team at the MRC Prion Unit has recently published the
above paper. A copy of the paper is attached at Annex 1.
Background
2. SEAC members were alerted via e-mail to the publication of this
paper on the Internet on 27th November 2002. The paper has now
been published in hard copy.
3. The researchers have previously reported (Collinge et al., 1995; Hill
et al., 1997) that Tg(HuPrP129V +/+ Prnp 0/0 )- 152 mice, which
express only human PrP V129 (129VV Tg152 mice), are highly
susceptible to infection with human prions from patients with
sporadic and iatrogenic forms of CJD, regardless of patient
genotype at polymorphic codon 129. However, these mice are much
less susceptible to prions from patients with vCJD. These data were
relatively reassuring, in that transmission of BSE to transgenic mice
expressing only human PrP was inefficient, with <40% of
intracerebrally inoculated mice succumbing to prion disease after
prolonged incubation periods, consistent with the presence of a
substantial transmission barrier. However, an important caveat with
respect to public health considerations was that vCJD was occurring
in humans of the PRNP 129MM genotype, while these mice
expressed human PrP 129V. Although classical CJD from patients
with all three PRNP codon 129 genotypes (MM, VV and MV)
transmitted efficiently to these mice, it is possible that part of the
transmission barrier to vCJD infection of these mice resided in the
mismatch at codon 129 between inoculum and host.
4. Using the same inocula, the researchers have now extended these
studies to mice expressing human PrP M129 to further study both
the bovine-to-human species barrier and the propagation of human
and BSE prion strains.
© SEAC 2003
2
5. These researchers have previously reported both FVB and C57BL/6
mice, when inoculated with BSE develop a BSE-like pattern with a
characteristic PrPSc fragment size and glycoform ratio BSE
(Collinge et al., 1996b; Hill et al., 1997). However, these
transmissions involve PrP from another mammalian species of
different molecular mass, such that the proteins are not directly
comparable, as with transmissions of human prion disease to
transgenic mice expressing only human PrP. This mouse PrPSc
pattern is, therefore, referred to as `diglycosylated dominant'. The
research team had also demonstrated that FIIIS and SJL mice
inoculated with BSE accumulate a glycoforms of PrPSc in a ratio
similar that found in human sporadic CJD and termed
monoglycosylated dominant.
Summary of paper by Asante et al 2002
6. The paper describes work investigating human susceptibility to
TSEs, using transgenic mice models (129MM Tg35 and 129MM
Tg45) which express the human form of the PrP gene. Mice were
inoculated with vCJD, sporadic CJD and BSE. As judged by clinical
disease, both mouse models were more susceptible to inoculation
with sporadic CJD, and less susceptible to vCJD and BSE.
Inoculation with vCJD and BSE resulted in both clinical and
subclinical infection, confirmed by human PrPsc detection in brain
tissue by western blot analysis.
7. This group has previously used western blot analysis to investigate
fragment size and the glycoform ratio of di-, mono- and
nonglycosylated forms of the disease-specific PrP protein, after
treatment with protease. The glycoform profiles of a number of TSEs
have been ascribed to different categories (or “types”) according to
their gycoform profile. In vCJD (or “type 4”), diglycosylated PrPsc is
the predominant gylcoform; a similar molecular “signature” has been
demonstrated in BSE. In this study, transmission of vCJD
(containing human PrPsc, type 4) to Tg35 and Tg45 mice resulted in
“faithful” propagation of human PrPsc closely resembling that of type
4 PrPsc in human brain. However, the most surprising aspect of the
study demonstrated that some of the Tg35 mice inoculated with
BSE also showed a molecular phenotype indistinguishable from that
of a sub type of sporadic CJD (“type 2”). This contrasted with Tg45
mice, inoculated with BSE, all of which showed a phenotype
indistinguishable from type 4.
8. The authors conclude that these findings further strengthen the
evidence that vCJD is caused by a BSE-like prion strain. They also
© SEAC 2003
3
suggest that the finding that transgenic mice, inoculated with BSE,
can produces a phenotype similar to that of sporadic CJD, could
raise the possibility that some humans infected with BSE prions may
develop a clinical disease indistinguishable from classical CJD
associated with type 2 PrPsc.
A more detailed summary of the experimental findings is outlined in
the following sections.
Section 1 Summary of results of transgenic mice (129MM TG35)
inoculated with sporadic CJD, variant CJD or BSE.
Section 2 Summary of results of transgenic mice (129MM TG45)
inoculated with sporadic CJD, variant CJD or BSE.
Section 3 Summary of results of 4 inbred mouse strain inoculated
with vCJD and BSE.
Section 1 Experiments in transgenic mice expressing human PrP
(129MM Tg35) inoculated with sporadic CJD, variant CJD or BSE
9. The researchers challenged transgenic mice homozygous for a
human PrP M129 transgene array and murine PrP null (129MM
Tg35), with inocula of sporadic CJD, variant CJD and BSE. The
transgenic mice were derived from an outbred strain. The level of
expression of human PrP in the brain of this transgenic line is
reported as twice that detected in a sample of (pooled) normal
human brain. Members may wish to note that a range of different
inocula were used in these experiments (see Table 1, page 6359 of
Asante et al. 20021) All but one of the inocula used in the
transmission experiments were prepared from individual patients or
animals (except 1038 which was a BSE brain pooled homogenate).
The BSE pooled homogenate gave a titre of 103.3 i.c.LD50
units when
titrated in RIII mice. A monoclonal antibody raised against
recombinant human PrP was used for immunohistochemistry and a
biotinylated form of this antibody was used for Western blotting.
1 Asante, E.A., Linehan, J.M., Desbruslais, M., Joiner, S., Gowland I., Wood, A.L., Welch, J., Hill,
A.F., Lloyd, S.E., Wadsworth, J.D.F. and Collinge, J. (2002). BSE prions propagate as either variant
CJD-like or sporadic CJD-like prion strains in transgenic mice expressing human prion protein. The
EMBO Journal 21 (23) 6358-6366.
© SEAC 2003
4
Results
10. The results are presented in Table 1 page 6359 of Asante et al. and
summarised in Figure 1 below.
Figure 1 Results of vCJD, BSE and sCJD inoculation in transgenic
mice expressing human PrP (129MM Tg35 transgenic mice)
Donor disease and PrP genotype of the inoculum
Recipient
sCJD
MM
sCJD
MV
sCJD
VV
vCJD
MM
BSE
Susceptibility
to clinical
disease
26/26 10/11 4/13 1/14 6/49
Incubation
time range
(days)
220 - 240 240 - 450 350 – 700 700 300 – 500
Change on
second
passage
no NR1 NR NR NR
Subclinical2 0 1 3/13 13/14 8/49
Florid
plaques
NR NR NR +3 +/-
1 NR - not reported
2 defined as not showing clinical disease but showing pathological and/or biochemical
evidence of disease by histology, immunohistochemistry and/or Western blotting
3 characteristic of vCJD in humans but rarely seen in mice
11. In the mice inoculated with vCJD, the type of PrPSc was nondistinguishable
from that seen in the brains of humans with vCJD
(with respect to proteinase K fragment size and the ratio of the
different glycoforms). The PrPsc type seen, as judged by PrPsc
fragment sizes was the same type 4 pattern characteristic of vCJD
prions in human brain. The glycoform ratio also closely resembled
that of type 4 PrPsc in human brain.
© SEAC 2003
5
12. The results with the mice inoculated with BSE were, however,
unexpected (Table 1 page 6359 Asante et al. and summarised in
Figure 2 here). Of the mouse brains tested by western blotting (11 in
total), 10 showed a molecular phenotype indistinguishable from that
of a sub type of sporadic CJD (type 2), while 1 was classified as
type 4. However, it is not possible, from the details provided in the
paper, to determine whether particular forms of the disease were
associated with particular inocula
Figure 2 Analysis of PrPsc type in 129MM Tg35 inoculated with BSE
Section 2 Results of vCJD, BSE and sCJD inoculation in transgenic
mice expressing human PrP (129MM Tg45 transgenic mice)
13. The researchers challenged mice from a second transgenic line
(129MM Tg45), which is homozygous for a human PrP M129
transgene array and murine PrP null, with inocula of sporadic CJD,
variant CJD or BSE. The brain expression of human PrP in this
transgenic line was four times that of pooled normal human brain.
The individual inocula used in each of the experiments are not
specified in the paper, however a sentence in the discussion
49 mice inoculated
35 unaffected
14 affected
6 clinical 8 subclinical
2 not tested 4 type2 PrPsc 6 type2PrPsc 1 type 4 PrPsc 1 not tested
Histopath
carried out
on 1/5
animals
Histopath
carried out
on 1/6
animals
1 no plaques
no specific
PrP staining
Plaques
© SEAC 2003
6
indicates that the same BSE inocula was used in experiments in
both the Tg45 and Tg35 mice. The results of the transmission
experiments are shown in Figure 3..
Figure 3 Results of vCJD, BSE and sCJD inoculation in transgenic
mice expressing human PrP (129MM Tg45 transgenic mice)
Donor Disease and PrP genotype of the inoculum
Recipient sCJD
not given
vCJD
MM
BSE
Susceptibility
to clinical
Disease
7/7 ¼ 0/12
Incubation
time (days)
150 580 >700
Change on
second
passage
No NR1 NR
Subclinical 0 ¾ 9/12
Florid
plaques
NR +2 +
1 NR - not reported
2 characteristic of vCJD in humans but rarely seen in mice
In all the Tg45 mice affected following vCJD or BSE inoculation, the
PrPsc type found was type 4, as expected.
Section 3 Results of vCJD and BSE inoculation to inbred lines of
non-transgenic mice
14. The researchers also studied the transmission of BSE and vCJD
in four inbred mouse lines (SLJ, RIIIS, FVB, C57BL/6). These four
inbred lines all have the same Prnp coding sequence (Prnp-a)
and are homozygous for methionine at codon 128, the
corresponding murine codon to PRNP codon 129. In the SJL and
RIIIS lines, BSE transmission is associated with the production of
a distinctive PrPSc type, with PrPSc glycoform ratios closely similar
© SEAC 2003
7
to that of human sporadic CJD and referred to as a
monoglycosylated dominant' PrPSc pattern. These lines are also
associated with unusually short incubation periods for BSE (Table
III page 6363 Ashante et al.) Both FVB and C57BL/6 mice when
inoculated with BSE develop a BSE-like pattern with a
characteristic PrPSc fragment size and glycoform ratio, referred to
as diglycosylated dominant'.
15. A BSE inoculum (1783) from a single bovine brain was used in
this experiment. This inoculum was different from that used for
the experiments in transgenic mice.
16. Following inoculation with either vCJD or BSE prions, both FVB
and C57BL/6 mice showed the expected diglycosylated dominant
PrP Sc pattern in the brain (Figures 2G) and a prolonged and
variable incubation period (Table III page 6363). However, in SJL
and RIIIS mice, the monoglycosylated form was seen following
inoculation with either BSE or vCJD. Although stable on further
passage in the same mouse line, the glycosylation pattern in SJL
and RIIIS mice was the diglycosylated dominant form when the
BSE had been passaged twice in C57/BL/6 mice. The results for
BSE are shown schematically in Figure 4.
© SEAC 2003
8
Figure 4 Inbred lines - Summary of PrPSc glycotype following BSE
inoculation
BSE
Mgd1 SJL, RIIIS FVB, C57BL/6
Dgd2
Mgd SJL C57BL/6 Dgd
SJL, RIIIS, FVB, C57BL/6 Dgd
1 Mgd - Monoglycosylated dominant pattern; 2 Dgd - Diglycosylated dominant pattern
17. The authors state that the neuropathology observed in SJL and
RIIIS mice inoculated with either BSE or vCJD showed only diffuse
staining for PrP without florid or other PrP immunoreactive plaques.
These data are not shown in the paper.
Key Conclusions
18. i) The species barrier is absent for transmission of sporadic CJD
from patients with a codon 129 MM genotype to transgenic mice
expressing a human 129 MM form of PrP.
ii) In this model, the species barrier for transmission from human or
cattle to mice was lower if pathological changes, rather than
clinical disease are the criteria used to indicate transmission.
iii) Some mice when inoculated with either BSE or vCJD prions,
developed the neuropathological and molecular phenotype of
vCJD, consistent with these diseases being caused by the same
prion strain.
© SEAC 2003
9
iv) Inoculation of BSE prions can induce two distinct phenotypes in
one of the transgenic lines examined (129MM Tg 45). 1/14
affected animals showed a molecular phenotype that was
indistinguishable from that of vCJD (type 4 PrPSc). 10/14
affected animals showed a molecular phenotype
indistinguishable from that of sporadic CJD (type 2 PrPSc). The
three remaining affected animals were not tested.
v) The sCJD like phenotype (type 2 PrPSc) was not detected in the
second transgenic line (129MM Tg45) examined after BSEinoculation
and 9/9 affected animals had the vCJD like phenotype
(4 PrPSc ) .
The authors suggest
19. i) The current definitions of the species barrier (quantified either by
comparative titration in the two respective hosts or by a fall in the
incubation period between primary and secondary passage)
should be reassessed because both depend on the onset of
clinical symptoms.
ii) The findings strengthen the evidence that vCJD is caused by a
BSE-like agent, and suggest that more than one BSE derived
prion stain may infect humans.
iii)Some humans infected with BSE may develop a clinical disease
that is indistinguishable from sporadic CJD associated with type 2
PrPSc.
iv)Some of the increase in sporadic CJD in the UK may be related to
exposure to BSE.
v) Other species exposed to BSE may develop prion disease that
may not be recognised (as been caused by BSE) by current strain
typing methods
Advice Sought from the Committee
20. Members are asked to advise on the scientific significance and
implications of this research in particular on, .
i) The experimental design (in particular on the influence of the
transgenic lines and different inocula on the interpretation of the
findings)
© SEAC 2003
10
ii) The conclusions and speculative interpretation of these data
(summarised in the covering paper)
iii)What are Members views on the implications of this work for
differential diagnosis in human and animal TSE’s ?
iv)Does this research indicate a need to include molecular PrP subtyping
in epidemiological studies of CJD?
List of material attached
• The scientific paper Asante et al., (2002) EMBO 21 (23) 6358-
6366
• Comments on the Asante paper ‘Mouse model sheds new light
on human prion disease’ (Published on the MRC Website)
References:
Collinge et al. (1995) Unaltered susceptibility to BSE in transgenic
mice expressing human prion protein. Nature 378, 779-83.
Hill et al., (1997) The same prion strain causes vCJD and BSE.
Nature 389, 448-50.
Lloyd et al (2001) Identification of multiple quantitative trait loci
linked to prion disease incubation period in mice. Proc Natl. Acad.
Sci USA 98, 6279-83. http://www.defra.gov.uk/animalh/bse/bse-science/SEAC2/papers/seac77_3.pdf © DEFRA 2003
1
PAPER No: SEAC 77/5
BSE EPIDEMIOLOGY IN THE UK AND OTHER MEMBER STATES
Issue
1. In the near future, it will become increasingly apparent whether the BSE
controls put in place in the UK have been fully effective in stopping the
spread of the BSE agent, and whether there may be other routes of
transmission that could affect the declining rate of infection. A major
active TSE testing programme, based on European Union legal
requirements, has been in place in the UK since July 2001. The
information gained from the testing programme is an important
supplement to that resulting from passive surveillance.
Advice sought from the Committee
None. This paper is for information only.
The declining UK epidemic
2. The key statistics are:-
• As at 6 January 2003, a total of 181,887 cases of BSE have been
confirmed in the UK. Only 33 of these cases have been confirmed in
animals born after August 1996 when the feed ban is considered to
have been fully effective (despite over 6 years now having elapsed).
• The BSE in cattle epidemic is declining at a rate of about 40%
annually. The epidemic peaked in 1992, when 37,056 cases were
confirmed in the UK. For 2002, 1,008 cases (identified through both
active and passive surveillance) have now been confirmed (with 107
results still pending).
3. The age structure of UK BSE cases continues to shift towards older
animals. Over 60% of cases now occur in animals which are 7 years old
or more. As the average incubation period of BSE is 4-5 years, this
indicates that UK control measures are having a major effect.
© DEFRA 2003
2
Forecasts
4. VLA forecasts for the decline of the BSE in cattle epidemic in Great
Britain cover cases identified through passive surveillance only:-
Year Central
estimate of
confirmed
cases
Lower 95%
confidence
interval
Upper 95%
confidence
interval
Actual
number of
cases
1999 2,083 1,774 2,392 2,254
2000 1,188 956 1,420 1,311
2001 512 360 664 781
2002 183 92 274 430
2003 61 9 113 …
2004 19 0 48 …
5. Experience shows that the actual number of cases typically follows the
upper 95% confidence interval of the VLA projections. However, the
number of confirmed cases in 2001 and 2002 is higher than this. The
FMD outbreak disrupted the slaughter of older cattle under the OTMS.
This has increased the mean age of the cattle population and resulted
in more cases than previously anticipated. Nevertheless, the epidemic
continues steadily to decline. The number of BSE cases born after mid-
1996 remains low, despite the fact that animals born in 1996 and 1997
are now approaching the peak age of clinical onset for BSE.
6. The UK is currently assessed under international rules as having a high
BSE risk status. Factors other than confirmed cases are also taken into
account in determining risk categories (such as imports of contaminated
feed or infected animals, and the possibility of cross-contamination of
cattle feed with feeds that contain mammalian MBM). However, once
the BSE in cattle epidemic has declined to less than 100 confirmed BSE
cases per million within the adult cattle population, it may be possible
for the UK to be classified in a lower risk category. In terms of risk
management, this may allow consideration of a more restricted range of
SRM controls.
How robust is the surveillance?
7. Additional BSE cases have been detected since 2001, following the
introduction of a major active surveillance programme, which is based
© DEFRA 2003
3
on European Union (EU) legal requirements. A total of 1,067 cases (out
of 498,801 animals tested1) have been confirmed in the UK through
active surveillance. In 2001, 318 cases were confirmed through active
surveillance from 78,852 animals tested. And in 2002, 578 cases were
confirmed (as at 6 January 2003) from a total of 385,705 animals
tested.
8. The results of the active surveillance (0.21% positive overall) do not
indicate any significant under-reporting of clinical BSE cases or of cattle
close to onset of the disease.
9. BSE has been confirmed in approximately 60% of the suspect animals
compulsorily slaughtered in 2002 as part of the passive surveillance
programme. This suggests that UK farmers are continuing to be vigilant
in reporting clinical cases of BSE. This is a legal obligation, and farmers
continue to receive full compensation.
Current EU position
10. The following table provides information on the total number of BSE
cases (clinical signs and active surveillance) in cattle over the last 18
months. This covers the period following the significant extension of
BSE testing programmes across the EU from 1 July 2001:-
Adult
cattle
(millions)
Cases
born
before
Aug. 1996
Cases
born after
Aug.
1996
Unknown
date of
birth
Total
cases
UK 5.0 1,808 31 0 1,849
Belgium 1.5 42 21 4 67
Denmark 0.9 1 5 0 6
France 11.2 387 35 0 422
Germany 6.5 118 31 0 149
Greece 0.3 0 1 0 1
Ireland 3.4 458 8 1 467
Italy 3.4 42 26 0 68
Luxemb’g 0.1 0 1 0 1
Neth’lands 1.8 19 16 0 35
Portugal 0.8 127 24 0 151
Spain 3.4 100 56 0 156
1 Most of the 498,801 animals were tested in the period between July 2001 and December 2002. However
this figure also includes all animals which were tested prior to July 2001.
© DEFRA 2003
4
11. Based on EU testing statistics for the period January to October 2002,
the BSE incidence per million adult cattle in major European countries is
as follows (excluding pending results):-
BSE clinical
suspects
Casualty
animals and
fallen stock
Healthy
animals,
BSE
eradication
Total
UK 83.2 100.4 2.2 185.8
Portugal 23.8 25 42.5 91.3
Ireland 25 46.4 8.9 80.3
France 3.5 9.2 5.6 18.3
Belgium 2 9.3 8.7 20.0
Germany 1.1 7.0 5.9 14.0
Spain 4.1 19.1 10.6 33.8
Italy 0 3.8 5 8.8
Holland 0.6 4.7 3.5 8.8
12. Following the introduction of major active surveillance programmes in
2001, the number of confirmed BSE cases in cattle showed an increase
in most EU member states, although this has now started to level out. It
continues to increase, however, in Ireland (242 cases reported between
January and December 2001, 288 in 2002) and Spain (82 cases
between January and December 2001, 121 in 2002).
BSE reported in non Member States
13. With the exception of Switzerland, the total number of BSE cases born
in countries outside of the EU is still very small:-
Year of
report
Pre-2000 2000 2001 2002 Total
Czech Rp. 0 0 2 2 4
Japan 0 0 3 2 5
Liechtenst. 2 0 0 0 2
Poland 0 0 0 4 4
Slovakia 0 0 5 5 10
Slovenia 0 0 1 1 2
Switzerl’d 333 33 42 18 426
© DEFRA 2003
5
EU control measures
Feed controls
14. An EU-wide ban on feeding proteins derived from mammalian tissues to
ruminants was introduced in 1994: the evidence does not suggest that
this was rigidly observed in most EU countries. From 1 January 2001,
Community legislation banned the use of a wide range of processed
animal proteins (including meat and bone meal) in feed for all farmed
animals.
Culling
15. Where BSE is confirmed in a bovine animal, Member States are
required to:-
• Kill the positive animal.
• Identify and kill all bovine animals belonging to the cohort2 of the
animal in which the disease was confirmed.
• Where the disease was confirmed in a female animal, to identify and
kill all its progeny born within two years prior to, and after, clinical
onset of the disease.
• Optionally to identify and kill all other bovine animals on the holding
of the animal where the disease was confirmed (depending upon the
local epidemiological situation);
16. The UK is exempt from some of these requirements on the strength of
the effective feed controls and the OTM scheme, which have operated
in the UK since 1996. Under EU legislation, the UK is required only to
identify and destroy the BSE positive animal and, where confirmed in a
female animal, all its progeny born within two years prior to, and after,
clinical onset of the disease. Presently, however, transitional measures
mean that the UK is continuing with its comprehensive offspring cull (i.e.
slaughtering all offspring born after 1st August 1996). Where the
positive animal has been born after 1 August 1996, the UK authorities
are also required to ensure that all cohort animals are excluded from the
food chain and are tested for BSE at the time of slaughter or death. This
is primarily for epidemiological monitoring purposes.
2 A cohort means all bovine animals which were either born in the same herd as, and within 12 months
preceding or following the birth of, the affected animal or reared together with the affected animal at any time
during the first year of their life and which may have consumed the same feed as that which the affected
animal consumed during the first year of its life.
© DEFRA 2003
6
Conclusion
17. Models of the epidemic indicate that BSE in cattle will continue to
decline in the UK. The major active surveillance programme will provide
further important information, helping to verify the progress of the
disease. BSE cases in cattle born after August 1996 will be carefully
examined and expert veterinary advice sought on the possible causes
of such cases for evidence of control failure of new routes of
transmission of the disease.
Department for Food, Environment & Rural Affairs
January 2003 http://www.defra.gov.uk/animalh/bse/bse-science/SEAC2/papers/seac77_5.pdf © DEFRA 2003
1
Paper No: SEAC77/6
Recent Developments from Defra’s TSE Research Unit
Issue
Members will be presented with an update on the Defra TSE Research
Programme (2001 to 2002).
Advice Sought from the Committee
None. This paper is provided for information only.
1. General Points
Since the emergence of BSE in 1986, Government has spent over
£140m on TSE research. Research is funded principally by Defra, DH,
FSA, BBSRC and MRC. Currently, the spend on TSE research by these
bodies totals around £30m per annum, of which Defra contributes
around £16.6m.
1.1. Research Budget
Following the Defra Comprehensive Spending Review (CSR)
settlement, the Department now has a fixed ceiling on the TSE
research budget. This is fully committed for 2002/3 and 2003/4
which leaves little flexibility for the inclusion of new work.
Proposed Research spend (£)
Baselines
ROAME Programme
2003/04 2004/05 2005/06
BSE in cattle 2,482 2,527 1,378
Diagnostics 2,668 1,514 1,500
TSEs in sheep 10,986 11,845 10,164
By Products 494 668 556
Risk analysis/
reviews/ workshops
49 45 40
Total 16,679 16,599 13,638
© DEFRA 2003
2
1.2. Science and Innovation Strategy
In line with the recommendations of the Defra Chief Scientific
Advisor, a Departmental TSE Science and Innovation Strategy
Document has been drafted. This is a statement of the
Department’s research needs to support the evidence base for
policy actions on TSEs. This is expected to be made public by May
this year.
1.3. UK Strategy for Research and Development Relating to the Human
and Animal Health Aspects of Transmissible Spongiform
Encephalopathies
The TSE research and development strategy in the UK was
previously presented in two documents:
• Strategy for research and development relating to human
health aspects of TSEs (published in November 1996 by DH
with MAFF, BBSRC and MRC input)
• Strategy for research and development relating to animal
health aspects of TSEs (published in July 1998 by MAFF and
DH with input from BBSRC).
In view of the growing overlap of science and the improved coordination
of TSE research in the UK, the UK funders of TSE
research and development are in the process of drafting a new
strategy document. The strategy will be released for public
consultation during May and June 2003 and is due for publication
in September 2003.
2. BSE – General
2.1. Key Research
Defra is continuing to support key applied research to maintain
policies that are in line with the new Departmental objectives and
PSA targets. In particular we will be continuing to fund the
epidemiology studies that will model and determine projections for
the progress of the disease in cattle. There will be particular focus
on the monitoring and analysis of information on the BARB group
of animals that have been born since the rigid enforcement of feed
controls in 1996.
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BSE – Specific
2.2. Minimum Oral Dose
Information on the minimal oral dose required for transmission of
BSE to cattle is important for supporting risk modelling and
epidemiology studies of BSE. Such studies are also important as
they provide information on the appearance of disease in cattle
that have been exposed to a range of doses. Similar sheep
experiments are also on-going investigating minimum oral dose for
sheep experimentally infected with BSE.
On-going Defra funded studies are examining the disease
transmission to cattle orally challenged with low single doses
(0.001g, 0.01g and 0.1g) of BSE.
2.3. Maternal Transmission
John Wilesmith, VLA, has recently informed us of further modelling
work performed on the data in the BSE surveillance database to
investigate the level of maternal associated risk. These studies
indicate that the cumulative maternal risk, based on the whole GB
epidemic data, is now reduced to 2%, but with a confidence
interval including zero.
2.4. Distribution of BSE Infectivity
Defra has supported extensive work to investigate the distribution
of BSE infectivity in cattle tissues. The testing of tissues in mice
has been underway since the early 1990’s. Present work is
examining the distribution of BSE infectivity in disease time-point
tissues of cattle orally challenged with BSE. This work is now
funded by the FSA.
The current study involves intra-cerebral inoculation of tissues into
recipient cattle to eliminate species barrier effects with mice. A
recent result has documented disease transmission to 1 recipient
bovine challenged with a pooled tonsil sample, collected from
cattle 10 months post oral challenge.
2.5. Tests to Monitor MBM for Ruminant Protein to be Evaluated by the
EU
The development of diagnostic tools to test for the adulteration of
compound animal feed with mammalian meat and bone meal or
other banned animal material, continues to be a Defra priority. The
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development of these tests will build on existing tests and
represents the primary control point for preventing future BSE
transmission to cattle.
Defra has several test development projects on-going and one
research and development project has recently been completed.
This is based on a molecular based DNA amplification method and
is claimed to satisfy EC test sensitivity requirements. It is
envisaged that further validation of this test will be required before
it can be adopted for routine use.
The EU is establishing a ring-trial to evaluate tests currently
available for monitoring compound animal feedstuff compliance to
legislation. The Veterinary Laboratories Agency has formally been
nominated to represent the UK’s interests in this trial.
2.6. BSE Strain Stability
Histological results from a recently completed Defra funded project
have indicated that BSE in cattle has remained uniform throughout
the course of the BSE epidemic. This provides some evidence that
a single agent was responsible for the cause of BSE and
subsequently has remained stable throughout the epidemic.
3. Diagnostic – General
3.1. Joint Funders Open Competition
The development of tests suitable for pre-clinical detection of TSE
disease in animals as well as those capable of differentiating
between prion “strains” has remained a priority for Defra.
A Joint Funders initiative for the development of diagnostic tests for
TSEs has resulted in Defra funding 10 new research projects in the
diagnostics area.
3.2. Pre-clinical Diagnostic Test
A major objective of TSE research has been the development of
one or more tests that may be used to identify TSE infection in live
animals before clinical signs are apparent. This is especially
important with these diseases because of their long incubation
periods during which they may pose a risk to animal health or
public health.
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Some progress has been made with the development of the I.C.E.
(immunocapillary electrophoresis test) test at the VLA. The method
has been shown to identify positive sheep from scrapie flocks at
certain stages of infection before clinical disease develops.
Further work is being done to determine the exact age range in
which positive animals can be identified. Scrapie-free animals give
negative results with the test. The method therefore shows
promise as a diagnostic tool but its use on a wide scale will be
determined by the final characteristics of the test, in particular the
optimum time for the test to be used to identify TSE positive sheep.
The preparatory stages for samples in this test are relatively
complex and require several days to process; this may limit the
number of samples that can be processed and the scale of use of
the test. Currently the I.C.E. method remains the only non-invasive
live animal test that has the development potential for identifying
TSE-infected sheep
3.3. Call for Research Using Spectroscopic Methods
Recently, Defra has been involved with the FSA and BBSRC in
holding a workshop on the application of spectroscopic methods
for TSE disease diagnosis and particularly for the differentiation of
BSE and scrapie. As a result of this workshop, a call for research
proposal was advertised at the end of last year with a closing date
for applications on 24 January 2003.1
The application of spectroscopic techniques, including mass
spectrometry may enable the structure of the prion protein to be
investigated and hence these methods may be useful for TSE
strain differentiation. Spectroscopic strain differentiation methods
would compliment on-going Defra funded work developing
methods to differentiate BSE and scrapie in sheep.
4. Diagnostic – Specific
4.1. Recent University of California (San Francisco) publication
Stanley Prusiner and colleagues has recently published data partly
as a result of Defra funded work. This publication states to have
developed extremely sensitive immunological and transgenic
mouse bioassay methods for BSE diagnosis.
1 http://www.defra.gov.uk/research/RRD/CTX0203.pdf
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4.2. Differential diagnostic test – EC ring trial
The VLA in its capacity as a European Reference Laboratory has
been commissioned to draw up the strategy for investigating the
possible presence of BSE in the sheep population. As part of this
requirement, the VLA will be conducting a ring-trial evaluation of
existing rapid molecular-based methods for differential diagnosis.
As well as methods developed by the VLA and two French groups,
Professor John Collinge of the MRC Prion Unit and Dr Jiri Safar
(California) have been asked to put their methods forward for this
trial. The test developed by Dr Safar was, in part, funded by Defra.
4.3. Second EC ring trial to evaluate five rapid tests for the diagnosis of
TSEs in bovines
Five new rapid molecular tests for clinical disease diagnosis of
BSE in cattle are currently being evaluated in an EC ring trial.
These tests will complement the existing 3 EC approved tests. The
report of phase 1 of this ring trial was published on 27 March
2002.2 Further validation of these tests on a large number of BSE
positive and negative brain samples, and in a number of
laboratories, is still on-going.
5. TSEs in Sheep – General
5.1. Current Research
The work funded in this area is generally in support of the National
Scrapie Plan (NSP) and policies in support of public health. The
Unit will continue to fund research in support of this high priority
area.
5.2. Impact of NSP on Production Traits
There is a possibility that the NSP may impact on certain
production traits in sheep and that this may inhibit farmers from
joining the NSP. Defra is not currently funding research in this
area which is becoming increasingly important. Although we have
received two related proposals, currently out to peer review, which
would allow us to perform research into the impact of the NSP on
production traits, our current financial constraints may prevent
these projects from being funded.
2Available on the Institute for Reference Materials and Measurements website
http://www.irmm.jrc.be/bse_1.pdf
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5.3. Impact of NSP on the Biodiversity of Rare Breeds
Defra is committed to maintaining the biodiversity of species in this
country. However the Rare Breed Survival Trust (RBST) considers
that the NSP will limit the genetic resources needed for the survival
of a number of the breeds. Defra are currently working with the
RBST and it is hoped that a research proposal will be established
to look at ways to enable the NSP to proceed with the minimum
impact on rare breeds. It is envisaged that this project will be
funded from the NSP budget but would be managed by the TSE
Research Unit.
5.4. Detecting Differences Between Scrapie and BSE
Investigating possible difference between scrapie and BSE in
sheep continues to be a high priority. To achieve this several
approaches are being investigated, in particular rapid molecular
tests exploiting recent developments in technology.
5.5. Carrier State
An area where there is increasing interest is investigating the
possibility of a carrier state in resistant sheep. Defra currently
funds a number of projects in this area. This work involves
analysing tissues from ARR/ARR sheep which have been
challenged with either scrapie (oral challenge) or BSE (oral and
intra-cerebral challenge) for signs of infectivity. These tissues are
being analysed by Western blot, mouse bioassay and
immunohistochemistry.
6. TSEs in Sheep – Specific
6.1. Recent ARR/ARR Result
Defra, in collaboration with the Institute for Animal Health, recently
reported that a New Zealand sheep of ARR/ARR genotype had
succumbed to intracerebral challenge with BSE. As ARR selection
is the basis of the NSP this result has now been discussed by the
SEAC Sheep Subgroup who concluded that although the new
finding did not establish that BSE could be transmitted to
ARR/ARR sheep by natural routes of infection, the possibility could
not be excluded. (See item 3 of the agenda for the SEAC 77
meeting).
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7. Other Developments
7.1. Environment Workshop
To complement Defra’s existing research a workshop was held in
April 2002 to identify research priorities in the area of TSE’s in the
environment.3 A number of research questions were identified
including the development of better prion or TSE infectivity
detection methods for application to the environment.
Unfortunately, constraints in Defra’s Research and Development
budget has not enabled work in this area to be funded.
7.2. Current Research
Defra is currently funding two research proposals in this area.
• The first is investigating whether susceptible TSE free New
Zealand (NZ) sheep succumb to scrapie after being exposed
contaminated environments. This will be achieved in a number
of ways including lambing both NZ sheep and natural exposed
scrapie sheep together, housing NZ sheep in lambing sheds
after the scrapie sheep have been removed and exposing the
NZ sheep to contaminated pastures. Following exposure the NZ
sheep are removed to a scrapie free facility and monitored for
signs of disease.
• Defra has also commissioned a study to investigate the
persistence and movement of BSE in open soil experiments.
This study has important implications for risks of environmental
transmission and contamination of ground waters. The study
may also provide important information to support assumptions
used in risk assessments (e.g. the hydrophobic nature of the
prion protein). Despite the importance of this project, the
progress of this work has been affected by delays in the project.
7.3. Independent Archive Advisory Group
The Veterinary Laboratories Agency holds approximately 60,000
tissues from TSE affected animals in its TSE Tissue Archive for
distribution to researchers world-wide who would not otherwise
have access to TSE infected material. It is a limited resource which
requires an effective management strategy to ensure the
distribution of tissues to researchers is fair, transparent and
appropriate. An Independent Archive Advisory Group (IAAG) has
3 A report of the Workshop can be found on Defra’s Website
(http://www.defra.gov.uk/science/Publications/TSE_WORKSHOP_30_04_2002.pdf)
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therefore been established to set the policy for release of tissues
and assess individual requests for tissues where the tissue is rare
or the request is unusually complex. The group is chaired by
Professor Sir Peter Lachmann from the University of Cambridge
and is comprised of five independent experts and representatives
from the European Commission, Defra and other Government
Departments.
The establishment of this group was recommended by the Review
of Defra Research 1995–2000 (‘the McConnell Review’). http://www.defra.gov.uk/ TSS
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