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12 March 2003
The Food Standards Agency reviews the OTMS rule
- are they going to scrap it?
Dr James Irvine
FRSE, DSc, FRCP(Ed), FRCPath, FInstBiol
Teviot Scientific Consultancy, Edinburgh & Perthshire
©James Irvine www.land-care.org.uk
(Filed 12 March 03)
The over thirty months scheme (OTMS) came into
force to prevent cattle over the age of thirty months from entering
the food chain. The purpose was to keep meat from cattle that might
possibly be suffering from the early stages of BSE from entering
the food chain. The dilemma has been to know when meat is safe to
eat, as there is no reliable and verified test currently available
that will indicate whether abnormal prions (the alleged infective
villains) are present or not in the early stages before clinical
manifestations of the disease occur in any particular beast.
There is also the problem that the Spongiform
Encephalopathy Advisory Committee (SEAC) scientists have been alarming
everyone with their concerns that, as BSE in cattle and vCJD in
man have such long incubation periods, we could be in for a major
epidemic of vCJD in man in the years to come (1).
Others disagreed (2). Certainly
until very recently they were warning us that it was too early to
say whether the number of cases of vCJD in man was still on the
rise (the small number so far being the tip of the iceberg), or
whether the rising incidence had now reached its peak and was now
on the turn downwards (3). Understandably,
the statistics would be very difficult to analyse on such minimal
data, as the total number of deaths from vCJD between 1994 and December
2002 is only 121. A further 8 had been diagnosed but were still
alive.
The period of maximum exposure for man to acquire
the incriminated abnormal prions through eating meat from BSE infected
cattle ended in 1990. The question now is whether or not it would
be possible through a risk assessment to relax the Over Thirty Months
Scheme (OTMS) whereby cattle over the age of 30 months were excluded
from the food chain (with few limited exceptions). This was the
topic of the open meeting held by the Food Standards Agency (FSA)
in London on 7th March 2003 (4).
What has encouraged SEAC and the FSA to consider
relaxing or even dispensing with the OTMS is the marked reduction
in the incidence of BSE in UK cattle (5).
There is no doubt this reduction has been impressive. What really
matters though is, not so much the percentage reduction over the
years, but whether or not significant risk still lingers in our
cattle that are now in this respect much healthier.
It is clear, and not surprising, that the incidence
of BSE in fallen stock and casualty animals that are already excluded
from the food chain is higher than in apparently healthy cattle
(5). The figures claim to show
that the number of animals diagnosed with BSE postmortem in a 1996/97
cohort was as low as 5 in 60,466 (0.01%) in 2002, and 0 so far out
of 18,228 in 2003, in each case excluding fallen stock or casualty
animals. However, we are not told in the information available on
the Internet which test for BSE was used in this context.
It is common knowledge that BSE in cattle can
have a long incubation period before clinical signs are apparent.
At what stage in the development of BSE could the tests used in
the present report detect the disease process? This would seem to
be a relevant question as we have been told of the major concerns
over the possible transmission of the alleged incriminating prions
by blood transfusion (6) donated
by, or the use of surgical instruments (7)
previously used on, patients that were subsequently shown to be
incubating vCJD but had not at the time been suspected of having
it. Furthermore, it has been reported that TSE in experimental animals
can be transmitted by blood in the incubating phase of the disease
(8).
As far as I am aware, there is still not a reliable
test for abnormal prions which can be used in a non-invasive manner
before slaughter of cattle, and which might indicate whether or
not the beast was incubating BSE. Land-Care carried an article on
a promising new method employing membrane technology which might
help achieve this, but the application of such a test is still a
long way off (9). Promising results
have been reported by a group at King's College London which is
attempting to develop an ante-mortem test for BSE based on the detection
of antibodies developed against bacterial proteins (10).
So it seems we once again resort to models to
help us try and estimate what the risk might be of transmitting
agents that could lead to vCJD in man if the OTMS was to be relaxed
or dispensed with (11). The
problem here is that most reasonably intelligent people (both scientists
and non-scientists who are not expert in the niceties of epidemiological
statistics) have difficulty in following the logic of the modellers.
Worries emerge about the major assumptions the modellers apparently
have to make, and whether these assumptions are justifiable. There
are also worries about the past record of modellers - a bit like
weather forecasters, they use a lot of science and make assumptions
and not infrequently (with apparent considerable confidence) get
things wrong (although they are improving). But is this a good enough
basis for doing a careful risk assessment over such an important
matter as vCJD?
If only we could get that Gradipore test (see
above) developed and validated quickly, or indeed some other form
of test with fearsome sensitivity and specificity for diagnosing
the earliest stages of BSE. However, we need to realise that it
is not always possible for science to produce advances simply because
we demand them.
The trouble I have with John Godfrey’s presentation
as seen on the Internet (12)
is that he persists in saying that the risk is much less than in
earlier years (which it undoubtedly must be) but does not explain
convincingly enough what the size of the present risk actually is.
Again it comes back to the statement that OTM cattle would be tested
for BSE - but what method was he proposing to use for that purpose
and what are its limitations? Where are the peer reviewed papers
on this matter? So far, I have been unable to find anything in the
scientific literature that fills that bill. Without it, how does
he and others intend to convince a rather sceptical public?
It would of course be very good news if the data
were really as good as this new stance by the FSA suggests.
If a relaxation of the OTMS rule is indeed justified
- and we all sincerely hope that it is - then how it is put into
effect must be properly thought out. Inevitably dispensing with
OTMS will mean some animals will test positive for BSE. How will
these animals be handled in the abattoirs? To suddenly operate a
complete about turn in the rules so that, all-of-a-sudden, all cattle
over 30 months of age could enter the food chain, would seriously
disrupt trading. It would seem more logical to introduce the new
permissive scheme more gradually; for example by gradually raising
the age from 30 months in progressive steps. This would also allow
for some appropriate education of the public. They would understandably
want to know what the evidence is that shows everything is now OK
as far as BSE and British beef is concerned, when up to the present
we have heard little but potential doom and gloom.
Dr James Irvine
© www.land-care.org.uk
References
1. National
CJD Surveillance Unit 10th annual Report (2001): www.cjd.ed.ac.uk/rep2001.html
2. Venters,
G. A. (2001). New variant Creutzfeldt-Jakob Disease: the epidemic
that never was. BMJ, 323: 858-61. (View
article).
3. Irvine, James
(2003). Current Assessment of the Future Prevalence of vCJD in the
UK.
(Filed 12 March 2003, www.land-care.org.uk,
click here
to view).
4. FSA Press
Release (2003). OTM Rule public meeting - 7 March 2003. (Click
here to view).
5. OTM Rule
Review: Stakeholder Representatives Public Consultation Meeting,
7 March 2003: BSE Statistics. (Download
PDF).
6. Risk of vCJD
from blood transfusion.
(Filed 2002, www.land-care.org.uk,
click here to view).
7. Has CJD been
transmitted to 24 patients through the inappropriate use of surgical
instruments?
(Filed 30 October 2002, www.land-care.org.uk,
click
here to view).
8. Hunter, N.,
Foster, J., Chong, A., McCutcheon, S., Parnham, D., Eaton, S., MacKenzie,
C. and Houston, F. (2002). Transmission of prion diseases by blood
transfusion. J. Gen. Virol., Published ahead of print (16 July 2002)
in JGV Direct as DOI 10.1099/vir.0.18580-0. (Download
PDF).
9. Detection
of Prions: Developing Technology.
(Filed 13 February 2003, www.land-care.org.uk,
click
here to view).
10. Wilson,
C., Hughes, L. E., Rashid, T., Ebringer, A. and Bansal, S. (2003).
Antibodies to Acinetobacter
Bacteria and Bovine Brain Peptides, Measured in Bovine Spongiform
Encephalopathy (BSE) in an Attempt to Develop an Ante-Mortem Test.
J. Clin. Lab. Immunol. Published online (13 March 2003) ahead of
print by Teviot
Scientific Publications. (Download
PDF).
11. Ferguson,
N. and Donnelly, C. (2003). Assessing the impact of changes to the
OTM rule on human exposure to BSE infectivity. (Download
PDF).
12. Godfrey,
J. (2003). OTM Rule Review. Stakeholder Representatives public consultation
meeting Friday 7 March 2003. (Download
Powerpoint Presentation).
Further Reading Recommended by Land-Care
Irvine, W. J. (2003). Clarification of the Possibility of Transmitting
CJD in Man by Blood Products.
(Filed 17 February 2003, www.land-care.org.uk,
click
here to view).
Haywood, S. and Brown, D. R. (2003). Transmissible Spongiform Encephalopathies.
Veterinary Times, 33: 8-10.
(Filed 28 January 2003, www.land-care.org.uk,
click
here to view).
Leake, Jonathan (2002). Test everyone for CJD, says Nobel Prize
winner. Sunday Times, 1 December 2002.
(Filed 9 December 2002, www.land-care.og.uk,
click here
to view).
Linklater, Magnus (2002). They drive us Mad with False Fears about
Mad Cows. The Times, 5 December 2002.
(Filed 9 December 2002, www.land-care.org.uk,
click
here to view).
Editorial comment. Predicted Future Incidence of vCJD in the UK
Population.
(Filed 2002, www.land-care.org.uk,
click
here to view).
The English Disease: Hugh Pennington's Comments on the BSE Inquiry.
(Filed 2002, www.land-care.org.uk,
click
here to view).
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