TUESDAY 16 MARCH 1999

MR BRIAN DICKINSON, MR JIM SCUDAMORE, DR CHRIS CHEESEMAN and DR GLYN HEWINSON

  560. What is the highest level of incidence in any county at present?
  (Mr Scudamore) I cannot give the exact figure, it is around 1.8, 2 per cent, in the South West.

  561. And the lowest level is 0?
  (Mr Scudamore) The lowest level is 0. I think one has to recognise, there are lots of parts of the country where we do not have a TB problem. In fact, I have got the figure here for the counties, 2.59 per cent is the highest one, but that is for a set of counties, Gloucester, Avon and Wiltshire; and the next one down is 1.83, which is Cornwall; and then the rest of them are well below that.

  562. Thank you. It is quite clear the disease is spreading widely throughout the country at present; do you think that pattern of spread is going to continue if further action is not taken?
  (Mr Scudamore) I think I would question whether it is spreading widely throughout the country. I think the first point is, it is spreading in certain areas within the country, so I think there is no question that it is spreading in terms of the number of outbreaks we are seeing in the South West. We are getting focuses in other parts of the country, like Staffordshire, where the number of outbreaks seem to be going up, but in other parts of the country we are getting sporadic outbreaks; we have always had sporadic outbreaks in lots of parts of the country. So I think the question really is, is it spreading throughout the whole country, or is it spreading in certain parts of the country, and is it leading those parts to go into what are currently clear areas.

  563. I wonder if I can ask you a couple of questions about badger numbers and badger densities, because this is obviously quite an important issue, with the trial. First of all, the density of badgers: am I right that in the Krebs report he took a countrywide density, whereas, for instance, the National Badger Group talk about a South West density, when they are talking about the numbers that will be culled as a result of the trial, so we have this disparity between them talking about 20,000 being culled and MAFF talking about 12,000? And, if we take the Putford area, you estimated that there were 500 badgers in that area, you actually caught 280, and so Professor Bourne has rejected your 500 figure. I wonder if you could give us a little bit of indication about how we ended up with these figures, and what you really think is the figure for badger density and the numbers that will be culled in the trial?
  (Dr Cheeseman) It is extremely difficult to give an average figure for badger density because it is so variable. The South West of England has the highest density of badgers in Britain, and some areas of the South West of England have the highest density of badgers anywhere in the whole of the range of the European badger, and we are talking about 25 animals to the square kilometre, that is a high density. If you move across the country, a low density would be fewer than five animals to the square kilometre; in some areas of the marginal habitat, there is about one badger to the square kilometre. And the limiting factor is really sett sites, so if there are not any sett sites, even in suitable habitat, there will not be any badgers. As far as Putford is concerned, the estimates that were given for Putford, the 500 figure was an estimate made by the field staff on the ground, to inform them as to what number of traps needed to be put out for the actual culling operation. It has to be done on the principle of saturation trapping, you have to use more traps than you expect to catch badgers, and the rule of thumb is you use twice as many traps as you expect to catch badgers; so the estimate of 500 was made in order to deploy enough traps for the culling operation. In the event, 238 badgers were caught. That was actually in line with the estimates that were made by myself and one of the members of the ISG, Dr Woodroffe; we estimated between 200 and 240 badgers, so it was about right. It is on the low side of badger density, but you have to remember that Putford has actually been culled in the past, and it is very difficult to estimate at what level the badger population is on its recovery phase. It has been subject to BROs several times, many farms there have been subject to BROs in the past, and that will have depleted or reduced the badger population to below the carrying capacity; so not knowing exactly where it was on the recovery phase it was important to deploy enough traps. Now I think the final part of your question was to do with the Krebs estimate of 12,500 versus the NFBG's of twenty.

  564. Yes; which one is the more accurate?
  (Dr Cheeseman) I would not like to say that either of them are accurate, or inaccurate. I think the Krebs estimate was based on an average density of about five badgers to the square kilometre in the trial areas, and adding the proactive and the reactive culling areas together you get a figure of about 12,500; but, again, it did not take account of the fact that many of those areas have already been culled in the past. So I think my prediction would be that the ultimate number of badgers removed, in all ten triplets, would be something lower than the 12,500 that Krebs estimated, but that is just my own personal guess, based on my knowledge of badger density and what has happened in the past.

  565. And just a supplementary on that, because we do not really know the numbers and the density, it is sort of open to a wide interpretation. We are concerned, obviously, about the persecution of badgers in the control sites in the trial, and that would, therefore, reduce the power of the whole trial. Why do you not radio-tag the badgers in the control sites so that we then have some idea of a wider picture of density of badgers generally, and then we would have a better picture of the number of badgers that we have got and how many we are taking out?
  (Dr Cheeseman) Yes, it is true to say that illegal culling of badgers in the `no control' area, that is the experimental control for the trial, is a serious problem; and that is a very good idea, actually, radio-tagging badgers in the `no cull' area could give us some important information. There is on the market a mortality tag, which would tell us when a particular badger had died, and if a sample of badgers could be labelled with mortality tags, it would enable us perhaps to get a better idea of the level of illegal culling. It is a very labour-intensive and expensive business to do that, and I think it would be probably impractical to do it for all ten triplets; but the audit is one means by which we should get some information on the level of illegal culling. And it is true to say that there is some resurveying of the `no cull' area in the Putford triplet, to establish whether or not there has been any interference.

  566. I wonder, Dr Cheeseman, if we could have a note of the cost of the mortality tagging exercise, not necessarily now but in writing afterwards?
  (Dr Cheeseman) I can certainly provide that.

  Chairman: That will be helpful, thank you.

  567. Gentlemen, between you, you have a wealth of experience in studying badgers; would you have concluded that badgers were the prime source, a source, or the exclusive source of infection for cattle?
  (Mr Dickinson) I would have thought we were going on the advice from Krebs that badgers are a significant source of infection in cattle in this country.

  568. Unfortunately, I did not list that in the categories I was putting out.
  (Mr Dickinson) I am sorry about that inconvenience, but that is actually the advice we are going on.

  569. I appreciate that. What other sources could be relevant to the infection?
  (Mr Dickinson) I think we are reckoning that, firstly, the position is not wholly proved, in any sense, and therefore there is a great deal of uncertainty, a point which I think Professor Krebs made when he appeared here before you, so that anything which we say is bound to be subject to that. Cattle to cattle transmission clearly plays a part. Badger transmission, it seems, is a very significant source. There may be the possibility of other transmission as well. And so, I think, one is allowing for all these possibilities in the work which we are now taking forward, because we have put forward a strategy which is designed to cover all the various options here, cattle to cattle, badger to cattle, and from other sources to cattle, and trying to make sure that we have got a complete programme.

  570. You see, we have some difficulty, when we follow these matters through, in that the control samples can be very variable; if there are a number of possible factors which would lead to the spread of TB into cattle, unless we control each of the elements which might be doing that, within the research sample, could the conclusions be flawed?
  (Mr Dickinson) There is obviously a risk of flawed conclusions, but what we are trying to do is to put in place a trial which will give as good an answer as one can get to the question where the infection is coming from. Now the trial which is taking place is not the only bit of research into this, there is obviously other research as well, but the culling trial, together with the associated work on the epidemiology, through the new TB99 questionnaire, is meant to investigate this. Effectively, we are saying that there are a number of variables which could come into the picture, which could influence the level of infection and transmission; we are putting those together into the trial and into the further work which we are carrying out, and we are expecting to be able to analyse it in such a way that the forces which are strongest will come out clearly and will be identifiable over the period of the trial. So that, although it will be difficult to quantify things, and that was what the Krebs report, essentially, was about, about trying to quantify the significance of the relative contributions of different sources, we will want to try to get that established in a better way than we have at the moment.

  571. I think, at the present time, we have some difficulty in understanding transmission between one creature and another; do we have any views about transmission of TB from cattle to badgers?
  (Mr Scudamore) Going back to your first question, I think I agree that badgers are a source of infection in cattle. I worked in Scotland for nine years and we got TB breakdowns in Scotland where we did not have any infected badgers that we knew about; so I think badgers are only one of the sources. But, as Brian says, it is a matter of the quantitative analysis of what percentage of the source. Regarding transmission, if you have infection it can transmit from animal to animal, therefore it can go from badgers to cattle, and we are not sure what the mechanism of transmission is, but, equally, it could go from cattle to badgers. If you had a very serious case, a big breakdown in a herd, with cattle excreting the bacteria, then it is possible that badgers could become infected.

  572. Do you feel, gentlemen, overall, that we are really, and I can understand why this may be, but sort of thrashing around in the dark on this subject; until we actually get to the bottom of the transmission cycle, we may not actually reach the sort of conclusions we want? But, moving on from that, do we know what proportion of the badger population is infectious, as opposed to merely carrying TB?
  (Dr Cheeseman) That, again, is a moveable feast, it depends on where you look. The prevalence of infection in badger populations can range from zero up to a very high prevalence of 80 or 90 per cent; and of those animals that are infected a small proportion, usually about 20 per cent, are infectious, and I have seen two sets of figures which put the number of excreting badgers, on average, at about 5 per cent. So it is rather low, there are only a few badgers around that actually excrete the disease. In terms of the risk that poses to cattle, if you have got a high density of badgers then, obviously, the risks are greater, if you have got a low density of badgers, on a simple arithmetic basis, the risks are much lower.

  573. The studies we are carrying out, will they actually be able to separate these two positions; in other words, it is possible, is it not, to have a large number of badgers that, in fact, have TB but are not infectious?
  (Dr Cheeseman) Oh, yes; yes, indeed.

  574. But will the survey show whether, in fact, there are infectious badgers within these groups, as opposed to badgers merely carrying TB?
  (Dr Cheeseman) Yes; all of the badgers that are caught in the trial will be subjected to full post mortem examination, and not only will it be established whether disease is present in the badgers but my colleague will be involved in spoligotyping, typing the actual strain of the organism, as well, and a picture of the pathology of the disease in the badger will give us an idea of the proportion of animals that are actually excreting. It is very difficult to establish that because you need to look at the carcase and establish in which body organs the disease is present, and if the disease is present whether there is a route for the bacilli to be excreted.

  575. But that is the crucial question, is it not, that the establishment of TB, in itself, does not take us very much further forward, does it?
  (Dr Cheeseman) The establishment of TB in an animal is just simply that that animal is infected, but to establish whether it is excreting tubercle is a much more difficult thing to do.

  576. Yes; and are you confident that we will be able to gain sufficient information in these trials to come to a conclusion on it?
  (Dr Cheeseman) It will be the best information that we can possibly get.

  577. Is that a reassuring answer; the best information we can get may be very little, on the other hand, is it quite a lot?
  (Dr Cheeseman) I think it is going to tell us an awful lot about the true picture, the epidemiology of TB in the badger populations, in these trial areas.

  578. The final question I have is Professor Harris' view that TB is only found in badgers which live in larger social groups of eight or more?
  (Dr Cheeseman) Yes, there has been some work done that established that there is a threshold group size of about six to eight animals; if the group size is smaller than that TB tends to decline to extinction, and if it is more than six to eight animals it will persist. At our study area, at Woodchester Park, we have found disease persisting in badger social groups over very long periods of time, and in some of those periods the group size was well below six; so I think it would be the wrong impression to say that the threshold is something below which the disease will die out, I think the disease can persist at rather low densities. But there is bound to be some sort of density-dependent relationship of this disease in badger populations, and it is something we do not yet fully understand; but the trial will—

  579. It is a sort of tenement theory, is it, a tenement theory of animal health; in other words, it is linked, is it not, to ill-health in humans believed to be linked to overcrowding?
  (Dr Cheeseman) It is certainly a stress-related disease, and in badgers stress can, we think, bring on the advance symptoms of the disease, and, for instance, pregnancy, lactation, in female badgers, they can actually still produce litters and rear those litters successfully whilst excreting tubercle, which is why the badger is such an ideal maintenance host for the disease. Badgers can reproduce quite successfully whilst the population is infected; it is not an important cause of death in badgers, it is a self-perpetuating wildlife reservoir.