Examination of Witnesses (Questions 140
- 159)
WEDNESDAY 7 NOVEMBER 2001
PROFESSOR DAVID
KING, PROFESSOR
MARK WOOLHOUSE
AND DR
BRYAN GRENFELL
140. We appreciate that.
(Professor King) So, to achieve that, we have to test
something like 300,000 sheep.
141. You are reviewing research into BSE in
sheep, and, after all, Richard Wilson was doing that only a few
years ago; what is new about your review?
(Professor King) What has simply happened is that
I have taken over from Richard Wilson as Chairman of the High
Level TSE Committee, and it seemed to Richard and the committee
that it was appropriate that the incoming Chief Scientific Adviser
should do that. And it is really in that capacity that I have
been taking a special interest in the current state of the fast
tests for BSE in sheep brain, in preparation for a meeting that
will take place in December of the High Level Committee.
Chairman: Thank you.
Mr Jack
142. The order of risk, Professor King, that
you have just given us, seemed to sort of resonate with me about
beef on the bone; and, if anything, maybe the numbers were even
bigger. But the Government of the day then decided to ban beef
on the bone, even though the order of risk was in your sort of
level of comfort, which you have just given us, about BSE in sheep.
What is the Government's current thinking on what is risk-free
within the statistical confines that you have defined?
(Professor King) Let me just correct the impression
that I have given you. I said, quite deliberately, that if you
take randomly 300 sheep from the sheep flock and test them you
would have this confidence that the incidence was less than 1
per cent. The tests were conducted on around 480 sheep that were
showing scrapie. That gives us much more confidence, because sheep
that are showing scrapie symptoms are the sheep that are more
likely to have the BSE, so the confidence level goes up very significantly.
143. That I accept, but you also said that to
bring it down to less than 1 per cent you were going to have to
do some more analysis, right, and then you quoted a further level
of risk that you hoped might result, if I have not put words into
your mouth, which would then enable you to respond positively
to the Chairman's question, which was, when could we say that
effectively sheep were BSE-free. Now what rang a bell in my mind
was that the lower order of risk which you defined, in saying
to the Chairman's question, yes, we could then say BSE-free sheep,
was of a similar order of risk to that which led the Government
to say, well, ban beef on the bone. So I am just really trying
to probe what are the risk factors which lead Government, at the
present time, to be comfortable that there actually is not a risk;
they seem to have different assessments of risk?
(Professor King) No. I think the Food Standards Agency
has been very consistent on this matter. And I think that it may
be a matter of my communication here, that if we do test scrapie
sheep that is where we are most likely to find the BSE, it gives
you a much greater degree of confidence if the sheep showing scrapie
symptoms do not have BSE; and already we have two significant
samples. I have referred to the one where the fast test has been
done, but there is another sample of 180, or so, sheep, and, Chairman,
I am not quite sure of these numbers, they were tested with the
mice assay, these again were sheep showing the symptoms of scrapie,
and those sheep again showed no BSE. So we have got two samples
of sheep that have demonstrated no BSE symptoms. So, effectively,
as against the cattle situation, where we knew there was BSE in
the cattle, as we stand now there is no evidence that there is
BSE in sheep.
Mr Martlew
144. Just on that point, because I think you
have answered my question, but we have never had a test on sheep
where BSE has been found positive, have we, in this country?
(Professor King) We have never had a test on sheep
in the field where we have tested positive; in the laboratory,
the test has been checked by deliberately seeding BSE into a sheep
in the laboratory and there the test shows the BSE.
145. Yes, but there is no evidence that any
BSE sheep have got into the food chain whatsoever?
(Professor King) There is no evidence of BSE in the
sheep.
Mr Mitchell
146. You told the `Today' programme that a diagnostic
test for BSE that produces results within 48 hours is currently
being validated by the VLA. What will this new test prove; can
it be used on live animals?
(Professor King) The VLA test that they are using
is a test that was developed by Professor Collinge in 1996, this
is the western blot technique.
147. He did it on mice, did he not?
(Professor King) He did it on BSE placed into mice
and on scrapie placed into mice, I believe, and showed that it
was strain-specific; but that still needs validation, and the
process being conducted at VLA is a validation process. But the
point I am making is that in validating that process they have
still not come across BSE in a single sheep that was showing scrapie
symptoms.
148. But the test is being validated, it is
not actually ready to go, as it were?
(Professor King) That is absolutely correct.
149. When will it be in a state of readiness
where it can be used quickly?
(Professor King) Can I give my own views on this,
and really the decision is for the Secretary of State in DEFRA
to make; but my view is that the validation procedure and the
testing procedure can be brought together into one. We are now
moving into a state where we are going to test for scrapie incidence
in the sheep population using a fast immunoassay, a fast test,
and for European purposes we are going to test around 20,000 sheep,
randomly, from the sheep livestock. So in that process we will
be testing for TSEs. Now what I am suggesting is that where we
find a TSE-positive, so we know it is either scrapie or BSE, we
should then do a further and more sensitive western blot test
to see whether it is BSE or scrapie; so we would then not only
determine the scrapie incidence in the sheep population, we would
also have some further confidence about the lack of BSE in the
sheep population. But this would also be part of the process of
validating the technique; in other words, I do not think we should
sit back and wait for a full validation process.
Chairman
150. Can I just ask, Professor King, there is
an enormous argument about validation; if we go back to BSE, well,
we are going to move on to BSE, but Professor Brown has argued
strongly that the equipment existed to do tests on live animals,
and, of course, that takes us into the argument about the need
for a contiguous cull, which is the great emotional issue in foot
and mouth disease. When I tabled questions to DEFRA, it was, oh,
well, it had not been validated and there had not been this trial
and the other trial; is there not any sort of internationally
accepted process of validation so we either know whether the wretched
thing works or does not work, and is available and is not available,
so at least we can argue about the substance and not about the
methodology?
(Professor King) I believe the answer to your question
is, yes, there is an internationally accepted validation procedure,
and within Europe that goes through the OIE. And you will be interested
to know that our own Pirbright Laboratory is effectively at the
head of that procedure, so that Alex Donaldson, the Director of
the Pirbright, is himself involved in that validation process.
151. As far as we are at present, and you have
just said that you wish to accelerate the validation process for
testing for BSE in sheep, and you think that can be run into sort
of practical trials, where are we on the validation process of
the tests for foot and mouth; is a tool available yet, or not?
(Professor King) I am going to ask Professor Woolhouse
to answer that, because he is certainly closer to the problem
than I am, and then perhaps I will come back.
(Professor Woolhouse) Dr Donaldson gave us a report
last week on the validation process particularly for Fred Brown's
FMD diagnostic tool, and the essence of that report is that in
the specifications provided by Professor Brown's team it did not
perform satisfactorily, and Dr Donaldson is in the process of
trying to enhance its capabilities to detect foot and mouth disease.
152. Do you want to add to that, Professor King?
(Professor King) I think that is an accurate description.
In the work at Pirbright, in enhancing the so-called fast-cycler,
which is Professor Brown's rather well-known technique, the technique
did not come through the tests very well; however, it is quite
clear that with a bit of tweaking it can be improved.
153. Right; so the technology is okay, the application
needs a bit of work on it?
(Professor King) Yes.
154. I am trying to put it in layman's terms.
(Professor King) The technology also needs improving,
Chairman.
(Professor Woolhouse) But, Chairman, it underlines
the need to go through a proper validation test, both for foot
and mouth disease, BSE, or any other infectious disease; you cannot
just jump into these things with an unproven test.
Chairman: No. We have no argument with that.
Mr Mitchell
155. Can I just check, the acoustics in this
place are very bad, did you say 480 sheep had been tested? Because
I read on the transcript from the `Today' programme, 2 November,
that 180 sheep's brains had been examined. Who is right, or has
there been some sudden onrush of—
(Professor King) Quite a number of figures are bandied
around. First of all, I have myself named two figures, and what
I will do in writing is clarify this point. I believe that 170
to 180 sheep have been tested using the mice assay at the IAH
in Edinburgh, and around 480 sheep have been tested using the
western block technique at the VLA.
156. Why has not this diagnostic test been developed
faster? There were allegations on the `Today' programme that it
was held back and insufficiently supported and inadequately backed,
because the labs represented producer interests rather than consumer
interests. Have you any comment on that?
(Professor King) I am interested in the same question
as you are asking me, and I am certainly pursuing that matter.
But what I would say is that we are talking about state of the
art scientific experiments here; these analyses are extremely
testing. The ability to distinguish one prion from another is
not trivial; if I say to you that the molecule is an incorrectly
folded protein, and the folding of the protein is the key to the
matter, the conformation of the molecule and distinguishing one
conformer from another is far from trivial. So we really are talking
about cutting-edge work. But, nevertheless, my straight answer
is, I think it is a good question.
157. The Animal Health Bill, if passed, will
allow Government powers to prohibit sheep from certain genotypes
susceptible to scrapie from being used for breeding, it could
cause them to be castrated, or whatever. Do we have the knowledge
to say which are going to be predisposed to this area?
(Professor King) There is some very significant work
that has been done on predisposition of different genotypes of
sheep towards scrapie, and this centres around the knowledge that
in New Zealand there are no sheep that are capable of picking
up scrapie. And there has now been DNA testing done, I think they
have so far picked up four codons that are specifically associated
with scrapie. So, in other words, the answer to this is, the science
has been done and it is a matter of testing the sheep population,
and that is in progress.
158. But the sheep in New Zealand are similar
breeds to the ones bred in the UK, are they not?
(Professor King) That is the very point, that they
are different genotypes; we have some overlap.
159. The Sheep Association says we do not even
know if there is carrier status, we do not even know it exists?
(Professor Woolhouse) Chairman, that remains another
one of these theoretical possibilities that we were discussing
earlier. The situation is that the sheep genotyping and its relationship
to susceptibility to scrapie is very well understood, but it does
need to be explored within two grounds; first of all, to make
sure that it applies to all breeds, whether from New Zealand or
not, and also whether there are any modifier genes, whether there
are more complex genetics that might affect these very well understood
patterns. But the genetics of susceptibility to scrapie is very
well understood.
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