Examination of Witnesses (Questions 180
- 199)
WEDNESDAY 7 NOVEMBER 2001
PROFESSOR DAVID
KING, PROFESSOR
MARK WOOLHOUSE
AND DR
BRYAN GRENFELL
180. Just one more, last one, which is really
to do with, I suppose, the concerns, because it was such a contentious
issue, the contiguous culling. You have made the point that the
disease spread from one premise to another, and so the contiguous
cull was necessary to take out, but evidence that occurred in
the Forest of Dean, and I am sure elsewhere had it, that when
animals that had been with people that were resisting the cull,
that they confirmed that none of them subsequently developed the
disease and they have all been since cleared by blood tests, providing
clear scientific evidence that the vast majority of contiguous
farms slaughtered were not infected and posed no risk of spreading
the disease, and that is certainly true in the Forest of Dean?
(Professor King) But you heard Professor Woolhouse
say that 50 per cent of infected premises were within one and
a half kilometres of the previous infected premise.
David Taylor
181. Those two facts are not necessarily inconsistent,
what Mrs Organ said, about the very large number of culled contiguous
farms showing no signs of disease; because is it not the case
that overzealous Ministry vets, driven by panicking politicians,
produced an unacceptably high level of false positives, in terms
of clinical diagnosis? I asked Mr Scudamore last week what the
level of false diagnosis was, by the time the results came back
from the laboratory, and he did not have the figure to hand, he
promised to write to the Chairman, and we still do not have that
figure. But are your models sufficiently sensitive to allow for
those relatively high levels of false diagnosis in the prime herd,
if we can call it that?
(Professor Woolhouse) That figure is a very important
figure. I can give you a rough estimate and provide written evidence
if you want, but it is of the order of 20 per cent over the course
of the epidemic. Now that is not a false positive rate, that is
not confirmed in the laboratory, and that depends on exactly how
sensitive the laboratory tests are in those field samples, so
you cannot just take that figure and assume that all those were
not infected with foot and mouth disease. The figure that you
mentioned, about the contiguous premises, you would not expect
those, very often, to show up positive on laboratory tests, because
the whole point of the culling programme is to try to catch them
while they are incubating disease, and, as we discussed earlier,
incubating disease really is not easy to diagnose at all, even
in the laboratory; so you would not expect that to happen.
182. The final point, Chairman, then, if there
was a slightly longer period between the slaughtering on neighbouring
farms to allow for the confirmation of accuracy of the clinical
diagnosis on the prime farms, would not that, could not that have
saved very, very large numbers of animals and effort and energy,
and so on?
(Professor Woolhouse) I think that is something we
do have to look at very carefully. But there is an underlying
principle to all those types of suggestion, I have a lot of sympathy
with that one myself, that is that the penalties for being wrong
with this disease are very severe; so if, by whatever extra checks
and balances you introduce, you actually miss a few more cases,
each of those cases has the potential to be very serious indeed,
to infect dozens or even hundreds more other farms. And that is
the sort of risk you have to balance, and that is where the epidemiological
analyses come in; it is a difficult to balance the risks, it is
a difficult job, but it is important to do it right.
Mr Breed
183. Can we take it then, from all the experiences
you have had over the whole of the foot and mouth crisis, and
where we are now, and bearing in mind we are debating the Animal
Health Bill on Monday, that all the lessons that you have learned
so far will not in any way change the current contiguous cull
policy, which when combined with the potential provisions of that
Bill next week will mean that there will be very little opportunity
for anyone, as they have done in the past, to prevent a contiguous
cull on their premises going ahead, and therefore we will pursue
exactly the same policy again only with the big, heavy boots of
the law behind it?
(Professor King) If I could take that, first of all.
I think what is absolutely clear is that, if the 24/48-hour policy
had been maintained, and from the beginning, then the extent of
this outbreak would have been considerably more curtailed than
it was, considerably more.
184. But you said you have not done modelling
on that basis; you said that all the modelling so far—
(Dr Grenfell) I said we had.
185. You have done modelling on the basis of
the experience?
(Dr Grenfell) Yes; on the basis of `what if', certainly.
186. You have; is that available then?
(Dr Grenfell) And a considerable reduction in the
numbers of animals culled and in numbers of infected premises,
if it had been possible to have a prompt 24/48-hour contiguous
cull from the start.
(Professor King) That has to be the strongest argument;
and until new scientific methodologies can be applied, such as
PCR technologies for fast assay of neighbouring farms, such as
new smart vaccines, then I think this is the process for bringing
an epidemic under control.
(Professor Woolhouse) Can I chip in, because I am
very sympathetic with the question. If foot and mouth reappeared
now, then, clearly, the current policy is the right one to pursue,
from all the analysis we have done. But I am very sympathetic,
and I think more research is needed to see how that policy can
be refined, I think that is very important.
Mr Mitchell
187. There are interesting differences emerging,
with the scientific community sort of chanting, "Kill, kill,
kill," and preaching the contiguous cull, and you are saying
now that if you had begun earlier the problem would have been
much smaller, and the reaction we are getting from farmers, by
e-mail, is that, in fact, it led to the destruction of a lot of
healthy animals, and there is a constant quotation of Alayne Addy,
an Exeter-based solicitor, who assisted 200 farmers to resist
the contiguous cull, and confirms that none of these 200 subsequently
developed the disease. There is quite a gulf emerging here?
(Professor King) There is no contradiction whatsoever,
Mr Mitchell, and I think this has to be emphasised, that if you
are taking out all contiguous farms, and we are saying that 17
per cent of those would have gone down, it means that the other
83 per cent would not have gone down, that is absolutely correct.
But, on the other hand, that is at that moment in time, and, as
has already been said, if you do not take out an infected premise
before it develops to the point of pumping virus out into the
air then you have another source of infection, and the number
of farms that will go down as secondaries could be enormous. So
if you want to bring it under control there is a sacrifice involved
in setting up this small—
188. The sacrifice is 83 per cent?
(Professor King) Eighty-three per cent of the local
farms at that point in time that were healthy; but if you allow
it to spread to neighbouring farms those farms themselves will
subsequently become susceptible. So it is a point that really
has to be taken on.
189. Yes, well, we could argue on that perhaps,
but just let me take up a point made by Professor Woolhouse. You
say that where a contiguous cull was only partially implemented,
inadequately implemented, or was resisted, there was a greater
spread of the disease. I wonder where your control points are
on this, because there must have been similar resistance, similar
delays, similar problems, in every area. So you have not got two
archetypal areas, one where everybody submissively allowed a contiguous
cull and one where it was bitterly resisted, you have not got
those two poles, it is a very mixed experience; how do you differentiate?
(Professor Woolhouse) I did not actually say that.
What I said was that 50 per cent of new cases turned up in the
immediate neighbourhood of a previous case; that is a figure across
the country. It actually holds up very well regionally, there
is not a huge amount of variation in that, and that is during
the period of which the contiguous cull was in operation, so that
the neighbourhood culling, the contiguous culling that was done
missed an awful lot of cases that were in the immediate vicinity.
That is what I said.
Mr Martlew
190. As the MP for Carlisle, I can probably
be classed as one of those panicking politicians. The reality
is, of course, that this was a policy that was brought in later
on, and the inference is, through this, that because there was
objection from farmers that was how it spread. But, initially,
MAFF were going onto farms, taking samples, sending them away
and waiting for results; that was probably a week, and sometimes
longer. So was it not a failure of the policy in the first instance
that we were not killing on suspicion? I was at a meeting with
the Prime Minister towards the end of March and the outbreak had
been going on for a month then, when he actually gave the orders
to kill on suspicion; what would have been the effect on the outbreak
if we had been killing on suspicion from the first day?
(Professor King) I am going to turn to Dr Grenfell
to pick that up; but let me say, in effect, we have answered that
by saying that if this policy had been in place from the beginning,
instead of happening, what you have just described—
191. The inference seems to be that it was spread
by farmers objecting. The reality is, the main spread was by the
failure of Government policy from day one?
(Professor King) Can I ask Dr Grenfell to answer that
one.
(Dr Grenfell) To reiterate what I said before, all
the models, diverse models, of different sorts, say that, because
of the intense local spread, that Mark Woolhouse's 50 per cent
figure dramatically illustrates, a prompt, 24/48-hour contiguous
cull, implemented from the start, would have resulted in a significantly
smaller epidemic and a significantly smaller number of animals
culled.
192. Yes, but it was not the inability to get
the animals killed that was the problem, it was the MAFF policy
of waiting for positive results to come from the laboratory before
they culled; is that not the case?
(Dr Grenfell) I will hand that one back to Professor
King.
(Professor King) The answer to your question is that
I got involved on 21 March, my colleagues got involved a little
bit earlier, by picking up data, and at this point they had enough
data. If I can refer to page 2, you can see that this is the point
at which modelling was being done, in fact, Professor Anderson,
who is sitting behind me, and his team were involved in producing
these models, we got involved at this point precisely because
the epidemic at that stage was, I use this term scientifically,
out of control. And that was why I got involved; as Chief Scientific
Adviser, I would not necessarily have got involved in this epidemic,
if I had not spotted that.
Chairman: On your own criteria of probability,
I think the answer to Mr Martlew's question you wanted to give
us was yes.
Patrick Hall
193. Three points, if I may. I have been trying
to follow this, with considerable interest. Can I just look again
at the 17 per cent infectivity probability argument, which I think
I was beginning to understand, and that is at a point in time;
okay. I suppose we do not know where that 17 per cent is, that
is a problem, but whether we do or we do not know that, and we
do not know that, when a confirmed outbreak exists, where an outbreak
is confirmed, if effective biosecurity measures were then introduced
everywhere, or certainly in the contiguous cull potential area,
would that not secure the situation, the 17 per cent would then
be revealed but the others would be protected, they are healthy
after all and they are protected by biosecurity? Unless you are
going to tell me, and this seems to be controversial, that the
disease can be spread by the wind, I have heard different stories
on that. Can you clarify?
(Professor King) The first thing is to say that the
models that my colleagues use are stochastic models and those
models do not ask the question how is the disease spread, the
models look at what is happening in the field—
David Taylor
194. Sorry, Professor King, stochastic?
(Professor King) Statistical chance. So what they
are saying is, the probability that this farm gets infected rather
than this one is just chance; and they do not look at cause and
effect, in other words, they do not look to see whether a farmer
has walked across onto his neighbour's farm and made contact with
the animals there and carried the disease, it is just done on
statistical charts. So we do not look at cause and effect in these
models; nevertheless, of course, cause and effect is an important
part of understanding the process. And your surmise is right,
if we improve biosecurity measures then you will reduce the probability
that we have just said, 17 per cent will tend to go down, and
the better you have your biosecurity, if you locked up every farmer
on their farm, so that there was no movement, no movement of vehicles
either, then it will improve, but you will not eventually stop
the disease from spreading totally. Now whether it is going to
be airborne, whether it is going to be dogs, or even possibly
rats, moving from one farm to another, there will be some process
that will carry it.
Chairman
195. Though it can be airborne?
(Professor King) I believe the answer is yes.
(Professor Woolhouse) Airborne transmission is not
regarded as a major method of spread in this epidemic; but the
problem is, which your colleague was alluding to, that for the
bulk of infections we do not know how they spread, DEFRA investigations
have not revealed a probable cause of spread. That is the problem.
Patrick Hall
196. I will not come back on that one, although
I would like to. Can I just move on to the second of three, and
just looking at whether there is an issue here. Professor Woolhouse
said that experience has shown that 50 per cent of the outbreaks
did occur within the danger zone; what about the other 50 per
cent, and is that significant?
(Professor Woolhouse) It is very significant; the
other 50 per cent includes a small fraction of cases that actually
arose quite a long distance from any previous case, again, not
always with any definite mechanism of spread. And that, of course,
has seeded a number of outbreaks some distance from the originally
affected areas. So, in fact, in a sense, we have the worst of
both worlds here; we have a lot of local spread but not all local
spread so we cannot contain the disease entirely that way, it
has the ability to get out of the danger zone.
197. So if the contiguous cull can address only
50 per cent and not the other 50 per cent, what does that say
about the logic of the arguments about the contiguous cull?
(Professor Woolhouse) That is an excellent question.
The crucial point is that the contiguous cull was required to
bring the epidemic under control, so to stop this exponential
spread that could have taken in goodness knows how many more thousands
of farms in the long run. If it had not been enough to do that,
obviously we would have had a very severe problem; if the rate
of spread had not been so severe that the contiguous cull was
necessary then we would not have recommended it. But we were in
that territory where the disease was out of control without the
contiguous cull.
(Professor King) Could I just add a figure that I
think is relevant to this. Of all of the cases, confirmed cases,
of the disease amongst the British farms, 1,069 were in the region
Cumbria and Dumfries and Galloway, and the next highest number
in any region is Devon, at 173; so we have really had an epidemic
that spread out from Cumbria, and a number of seeding points there.
But I want to stress this point, because it is a local spread,
we did not see it go into a number of high-density animal areas
around the United Kingdom.
198. One last point. Given the very solid advice
from you and others, all of you, I mean, in support of the contiguous
cull, under current scientific capability, do you think that the
existing right of a farmer to appeal to the district Veterinary
Service regarding a proposed cull, which exists, as I have just
said, and will continue to exist, under the provisions of the
Bill, do you think that right of appeal is unhelpful and should
be abolished, because it delays, and, therefore, as you have explained,
could lead to a worsening of the situation?
(Professor King) I think we would have to say that,
from a purely scientific viewpoint, anything that causes a delay
runs the risk that Dr Grenfell referred to earlier, and my colleague
Professor Woolhouse, we both see this as statistical risks, and
anything that delays the culling of a potential viral centre is
a real risk.
(Professor Woolhouse) Can I make one more general
point in support of that. With any decision process of that sort,
remember, the risks of being wrong with this disease are so severe,
that is the problem; we pay disproportionately for being wrong,
where there is foot and mouth where we hoped it was not, and that
is a very serious situation.
(Professor King) It might be useful if I put a timescale
on this. We are talking about neighbouring farms being exposed
to the disease. The critical thing is that there is an incubation
period, and the incubation period for an animal exposed to this
strain of the virus is around three to five days; over that period
of time the animal is beginning to build up antibodies, but the
virus is building up in the body as well. At the point at which
its symptoms are shown, it is already into about the seventh day,
and the virus is already being emitted by the animal. So that
is the sort of timescale you are talking about; you have got a
very narrow window of time to get ahead of the disease. And, I
am going to stress this, the only way you can stop an epidemic
is to get ahead of it, and to get ahead of this you have to take
out the animals while they are incubating and before they come
to the viral emission stage.
199. And are you saying that vets cannot actually
identify that window?
(Professor King) You cannot see it; you cannot see
it.
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