Examination of Witness (Questions 87-99)
DR CHRIS
CHEESEMAN
MONDAY 10 FEBRUARY 2003
Chairman
87. Chris, you have tried manfully over many
years to try to explain the science of all this to me, so you
are going to have a go at various other people as well. I think,
just by way of an introduction, it would be quite useful, in about
three minutes, to explain what you have been doing over the last
20-odd years at Woodchester and how it relates to both previous
people's evidence-giving?
(Dr Cheeseman) Thank you, Chairman. To
summarise 25 years' work in three minutes is going to be a problem.
Basically, we were given the remit, back in 1976, when we started
our project, to investigate the role of the badger in the TB problem
in cattle. What we have accumulated in the last quarter of a century,
I must not keep reminding myself of the timescale, but it is a
long, prospective study, and we have a huge database which has
taught us a lot about the population dynamics of badgers, about
the epidemiology of the disease in badgers, about the way badgers
behave, particularly about the way diseased badgers behave. So
it is biological and more focused on the ecology and the behaviour
of badgers in relation to how this disease, if indeed it is transmitted
from badgers, gets into cattle. So a large element of our work
has been actually on the husbandry side, focusing on the risk
factors, and we have pinpointed certain situations which we consider
to be high risk, farm buildings particularly and places where
cattle are fed, and we have work in progress at this moment that
is trying to expand the identification of these risk factors,
to be able to give advice to farmers on what measures they could
usefully take to reduce the chances of their cattle getting TB.
We have projects looking at the involvement of other wildlife,
which you may like to hear more about, and I will leave that to
you, that is species other than badgers that may be implicated
in this problem. In the future, we anticipate being involved in
the development of vaccines, we have work already which is relevant
for this, but, for example, if it is going to target badgers you
have to develop a delivery system, it will have to be an oral
vaccine, so developing a suitable means of delivery is going to
be quite a challenge. We are looking at badger genetics, population
genetics is important, questions like is natural immunity to TB
a factor in badger populations, if so, the very last thing you
would want to do is take out that component of the population;
so this is one of the potential downsides of control. Allowing
a population to develop natural immunity is a very desirable thing,
and some of the culling policies that have taken place in the
past may indeed have had that negative impact. Another aspect
of our work is concerned with what we call the perturbation effects,
what happens when you remove badgers from the eco-system, is the
disease exacerbated by the disruption that takes place when you
take badgers out. Because there is no doubt about it, if you remove
a large component of a badger population the behaviour of the
remaining badgers is highly disruptive, they move over greater
distances, there are probably more interactions between badgers,
and one of the critical factors in any disease is what is called
`contact rate'. If one animal contacts and gives disease to one
other animal, at least, you have an epidemic on your hands; if
it is fewer than one, the disease will decline to extinction.
So anything that exacerbates, or promotes, contact is bad news,
and the perturbation effects are something that exercises our
minds at the moment. In relation to the trial, we are looking
at the impacts of removing badgers in the eco-system in terms
of what happens to the other species. One factor, just as an example,
to exercise your minds, if you took badgers out, they are key
species in the eco-system, they may have an impact on rabbit populations,
remove all the badgers, or a lot of the badgers, you may have
more rabbits. Ground-nesting birds is another phenomenon, it has
been suggested repeatedly that badgers impact on ground-nesting
birds in a negative way, and this is something that will come
out of our study, because that is one of the aspects that we are
looking at. So there is a very wide range, a huge, very broad
research programme. Woodchester Park, in Gloucestershire, is our
study area, that is one of the worst affected areas in the country,
so we chose Woodchester Park, which has a high density badger
population, for the focus of these studies. One of the criticisms
that has been levelled is that the data that is emerging is from
just that one population; my answer to that is that it is the
only data we have got, we would very much like to have lower density
data, but it is all that we have got to be able to model the disease.
I have not mentioned modelling, by the way, another aspect of
our work is modelling, and we are using the data that we have
generated to construct models that could be used in a predictive
capacity to see what impact certain strategies might have on controlling
the disease in cattle.
Diana Organ
88. I did ask Elaine beforehand, and she did
not really know because that is not her field, about the badger
population, and she gave a ball-park figure of about 300,000,
and I wonder if I could ask you a couple of questions about what
you think the badger population is, are they growing and thriving?
They joked at me about this, that they quite like to live in these
sort of habitats, which is where we are, in the South West, but
it does seem to me that that is where they seem to be. I drive
along the roads of the Forest of Dean and I see a dead badger
virtually every week, and that is not because my constituents
are worse drivers than those anywhere else in the world, I think
it is because there are a load of badgers there. So I wonder if
you can just give us some information about your estimate of the
badger population, the regional differences and where they like
to be and what kind of habitats they like, and the problems of
that, and are they moving into new areas? Because if we have got
the spread of TB, do we have a situation where actually the badger
population stays in one area but TB is going all over the place
where there are badgers, or are the badgers going where the TB
is, or the TB going where the badgers are?
(Dr Cheeseman) Elaine pointed out, quite rightly,
that the only surveys that have taken place are the two national
surveys, one in the mid eighties and one in the mid nineties,
and they both relied on counting badger setts to estimate numbers.
You can extrapolate crudely from setts to populations, and the
last survey put the population at about 300,000-plus adult badgers,
and it is increasing, on the whole, nationally, there are places
where it is going down, there are places where it is going up.
I would go along with that estimate. I was asked to put my own
estimate on it before the first national survey, and I think I
got within about 20,000, just as a guesstimate, you can do that
with knowledge of the sort of density they live per kilometre
square, and you just multiply up the range of densities and the
land mass that we have got that will support badgers.
Mr Mitchell
89. What area are we talking about, England,
England and Wales?
(Dr Cheeseman) England, Wales and Scotland. The majority
of badgers are concentrated in the south and west of the country,
the second part of your question. The habitat in the west of England
is absolutely ideal for badgers, indeed it has been suggested
that we are farming badgers, because we have created optimal conditions
in certain areas, the pastoral system is largely responsible,
and badgers' principal food source is earthworms, they like short-grass
pasture, the more heavily the grass is grazed the more easy it
is for badgers to find earthworms, and areas that support the
dairy and the beef industry also support high densities of badgers,
so the two seem to go together. However, there is a huge caveat
here, it does not follow necessarily that the more badgers there
are the more disease you will get in badger populations; there
is no linear relationship between the number of badgers and the
prevalence of TB in the badger populations. Indeed, at Woodchester,
we have got a population that has doubled over the period of study,
the density of badgers has doubled, and the disease has cycled,
with about a seven-year periodicity, and it has gone from highs
of perhaps 10% or more to lows of very nearly zero. And that is
one of the puzzles, because I was taught, as most ecologists are,
that diseases are usually density-dependent, the greater the density
of the host species the greater the prevalence of disease; that
is not the case with TB in badgers. So it is a complex problem,
and that is one of the points I would like to make at this juncture,
perhaps, for your understanding, it is not a simple issue that
the more badgers there are the more TB there is.
Diana Organ
90. Also, the other question, which I think
was quite crucial, about the expansion of TB in cattle has gone
into areas of Staffordshire and up into the Cheshire Plain, but
the concentration of badgers, does that overlay, or is there a
mismatch between where we have TB hot spots and TB spreading and
a growing population of badgers, or is there a smaller population
of badgers?
(Dr Cheeseman) I think Jan Rowe mentioned earlier
that most of the hot spots coincide with high densities of badgers.
There are some anomalies, there are some areas where cattle TB
seems to occur where there is very little, or even no, TB in badgers,
that we know about; so it is a question of perhaps if we looked
we might find it. I think, on the whole, there is a correlation
between the distribution of the disease in badgers and cattle,
but I do not think we should look into it any further than that
and deduce a causative effect. That is what the trial is all about;
the purpose of the culling trial is to see whether killing badgers
has any impact on the disease in cattle, and that will tell us
that fundamental question.
Mr Wiggin
91. Am I right to say, if this is not a population
density disease in badger population, then it is highly unlikely
that the culling, if it reduces the density of the population,
will have any impact; unless you specifically cull exactly the
right badgers, which are the ones with the disease, it is not
going to work, is it?
(Dr Cheeseman) It will make it worse. Culling, with
the disruptive effects that I have described to you, and the possible
removal of disease resistance in the badger population, could
actually make it worse. And some farmers said to we scientists
before the culling trial began, "If it had not been for Defra
killing badgers on a neighbouring farm, where there happened to
have been an outbreak, I wouldn't have got a problem, because
my badgers were healthy, and the population's been stirred up
and now I've got a diseased population whereas I had a healthy
one before." And that is a perfectly valid point.
92. Right; so really Defra should be working
on the vaccine and forget about the whole—
(Dr Cheeseman) No, no; please do not misunderstand
what I said. We do not know the contribution of the badger, I
do not know whether you are going to get onto the culling trial,
but there are two things to say to you here. The culling trial
had two objectives. One was to quantify the contribution of badgers
to the TB problem in cattle; that objective has gone, it no longer
exists, because we compromised the culling strategy that Krebs
had envisaged. He was talking about taking out all of the badgers,
and if you take out 100% of the badger population and you get
an effect you can say that it was because of the badgers; as it
is we are removing, at best, about 80% of the badger population
in the proactive strategy, and I have already explained to you
about the disruptive effects that could make it worse. So there
is no way the trial will quantify the contribution of badgers
to the TB problem in cattle; however, what it will do—
Mr Mitchell
93. What is the purpose of them then?
(Dr Cheeseman) What it will do is satisfy the second
objective—
Mr Mitchell: Can you prove anything from an
80% cull as opposed to a 100% cull?
Diana Organ: There is only enough proactive—
Chairman
94. Let him finish.
(Dr Cheeseman) I am just about to put your mind at
rest. The only point to the trial, believe me, and I do strongly
support the trial, for this reason, it will tell us whether killing
badgers has any impact on the disease in cattle, and it is absolutely
crucial, because that question has never been answered. The two
strategies, the proactive and the reactive culling, are not taking
place as designed by Krebs, it is true, so that is why that first
objective has been compromised. The second objective is intact,
and it is absolutely crucial that we satisfy that, because, as
I have already admitted to you, I have been involved in this a
long time, and right at the beginning we were asking Defra, or
MAFF in those days, to test the strategy that they employed to
see whether it had any impact. And I was extremely pleased when
Krebs recommended those trials, there were a lot of critics, but
I think just about every scientist in the community was extremely
pleased that, at last, we were attempting to underpin policy with
science. I suppose we have to say that we have been slightly disappointed
in the implementation, I think the delays are regrettable but
probably unavoidable. And I must say this also, I think that the
ISG, Defra, the Wildlife Unit of Defra, everybody concerned has
done absolutely everything they can to make this trial work, and
it is no fault of anybody that we have had foot and mouth and
other things, and it is true that foot and mouth has compromised
the trial probably in its duration and particularly with respect
to the reactive strategy, it has imposed all sorts of additional
limitations that are going to make interpretation difficult; but
nevertheless the trial is still important. I would say, if the
trial is abandoned, for whatever reason, what else is going to
happen; and I would hate to see us return to the old dogma of,
well, I am afraid we have heard some of it already today, there
is one camp that says "Kill badgers, because that's the answer
to the problem," there is no scientific basis to that, and
there is another camp that says, "Leave them alone because
they're not involved," there's no scientific basis for that
either. And I would like to see a scientific underpinning of future
policy, and therefore the trial is extremely important.
Mr Wiggin
95. But the other alternative is to vaccinate
and forget about badgers at all and actually focus our efforts
on curing the disease, which would have been a constructive and
a better use of taxpayers' money?
(Dr Cheeseman) We have heard something about vaccine
today.
Chairman
96. We are confused now, about the whole status,
of what is being vaccinated, with what and what is happening internationally?
(Dr Cheeseman) Would you like me, Chairman, just to
elucidate vaccines and the options, and the pros and cons? Can
I preface this by saying that perhaps I am not the best person
to ask, I think we should put these questions to the ISG, who
have some expertise that is better than mine.
97. We will.
(Dr Cheeseman) But I think vaccine is looked at as
being a panacea, by some parties, and it is not, either cattle
or badger vaccines. It is true that the option has been there
for a long time, and it is still being said that it is a long
way off, and you will be aware that the ISG have a sub-committee
at the moment looking into the prospects of vaccine for badgers
and cattle; they are due to report at Easter. I have been a member
of that committee and heard all of the deliberations and I should
say this, that it is extremely complicated on both sides, badgers
and cattle vaccine. If we take badgers for a moment, delivering
a vaccine to the badger population, we do not have an effective
vaccine, or, at least, we do not know whether BCG might work,
there is some evidence that it works in New Zealand on possums,
and the Irish currently are trying the vaccine in captive facilities;
but it is not a very effective vaccine, even for humans, so I
doubt very much that it is going to be very effective on badgers.
And we have two factors to take into consideration, one is the
efficacy of the vaccine, and, two, the proportion of the population
that you can actually get the vaccine into. So if you have a vaccine
that is 50% effective and you can only deliver it to 50% of the
population, you have only got 25% coverage, so that is the kind
of issue that we are up against immediately. Also you have to
take into account the fact that I do not think it would be a realistic
policy to introduce a vaccine with the intent of eradicating disease,
it would not happen, TB is too widespread in the badger population,
and you would be committing yourself to a very long-term strategy
even to attempt that. So vaccine would have to be administered
at least annually, probably twice a year, to make sure that every
cohort of cubs, and remember badgers breed once a year, so you
have got to make sure the cubs get vaccinated, to have any chance
of succeeding. If cubs are infected before they come above ground,
which is the first opportunity we could deliver an oral bait,
we have got a huge problem, and there is already evidence that
pseudo-vertical transmission, that is transmission from the sow
badger to her cubs in the sett, may be an important component
of this disease maintaining in badger populations; and if that
is the case it is another, really serious, confounding factor.
So we have not got an effective vaccine, and even if we did have
it would be a very tall order to make it work. And perhaps, Chairman,
if I can suggest that the cattle side is even more complicated,
I will not go into that, but it would require policy changes which,
I am not a politician I am just a scientist, but we export a lot
of bloodstock from this country and we cannot export vaccinated
animals, they have to be disease-free; those sorts of issues are
big political issues for the EC and others to consider. And, with
cattle, Jan Rowe also mentioned that a vaccine would have to give
cattle protection without compromising them against the skin test,
and that is not the case with BCG at the moment, although it is
a technical possibility that it could be developed in that way.
But, again, there are huge hurdles to be overcome to develop an
effective vaccine. We have heard mention of sub-unit vaccines,
and sonicated; these are bits of DNA, if you like. The vaccines
are usually live vaccines, and these are the most effective. The
problem with sub-unit vaccines is that they are not as effective,
and the only alternative is genetically-modified vaccines, and
I am sure I do not need to tell you that there would be problems
with implementing something like that. So I would just like to
leave you with the idea that vaccines are hugely problematic.
Diana Organ
98. We do not have a live vaccine for use on
the wild badger population for their TB, is that what we are saying,
we have not got that yet?
(Dr Cheeseman) BCG is a live vaccine.
99. Because you said that the human one does
not really work terribly well.
(Dr Cheeseman) That is right.
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