Select Committee on Environment, Food and Rural Affairs Minutes of Evidence

Examination of Witnesses (Questions 180 - 199)



  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.


  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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