Letter dated 18 December 2007, from Sir
David King, Chief Scientific Adviser to HM Government and Head
of the Government Office for Science
BADGERS AND
BOVINE TB REPORT
I have seen the comments sent to you by John
Bourne and his former colleagues on the ISG and by Professor Denis
Mollison in response to my report on badgers and bovine TB in
cattle.
Mark Woolhouse, Tim Roper and I have subsequently
had a constructive meeting with John Bourne, Christl Donnelly
and Rosie Woodroffe at which we discussed our respective reports
and their subsequent comments. We all agreed on virtually all
of the key scientific issues.
We agree that the scientific data support the
conclusion that culling gives an overall beneficial effect on
TB in cattle in those areas where there are high and persistent
levels of TB in cattle, providing the culling of badgers:
— is done competently and efficiently;
— covers as large an area as possible
(265 km2 or more is the minimum needed to be 95% confident of
an overall beneficial effect);
— is sustained for at least four
years; and
— the culled areas have "hard"
or "soft" boundaries where possible.
We also agreed on the ecological effects, considering
that badger culling prompted:
— immigration of badgers into
culled areas;
— disruption of badger territories;
— expanded ranging of badgers;
— reduced clustering of infection
in cattle outside the culled area;
— reduced clustering of infection
in badgers; and
— elevated prevalence of bovine
TB within the decreased population of badgers.
Although it does not alter the conclusion that
culling could have an overall beneficial effect, one substantial
area of disagreement between John and me is over the biological
plausibility of the results obtained between the first and second
cull. As both the Godfray report (2004)1 and More et al
(2007)2 note, there is a need to link cause (culling) and effect
(herd breakdowns) within a plausible timeframe. Including the
results from the first to the second cull reduces (but does not
remove) the overall beneficial effect of culling on herd breakdowns
seen in the RBCT results. Discounting the initial year of results
increases the beneficial effect and decreases the deleterious
edge effect.
John and I also differ on the extent of the
overall beneficial effect. He considers that it is "modest"
whereas I consider that it is much more significant and that the
benefits will increase over time with sustained culling. Since
the end of the RBCT, Christl Donnelly has been monitoring the
incidence of TB in cattle in and immediately outside the proactively
culled areas. Christl is continuing this monitoring and further
data will become available in the new year.
John's support for the conclusion that there
is an overall beneficial effect can be found in peer reviewed
papers (Donnelly et al, 2007; Donnelly et al, 2006)3,
4 that he and ISG colleagues published ahead of the ISG's final
report. He acknowledged this when he appeared before your Committee
on 24 October and has confirmed it in his answer to question 5
of your follow-up questions in which he says "Our analyses
indicate that modest overall benefits could be obtained by culling
badgers in a simultaneous and coordinated fashion, over large
areas of the countryside and repeating such culls over several
years".
I am disappointed that, in their final report
and again in their letter to you, the ISG chose to dismiss this
conclusion, not for scientific reasons, but on the basis of assumptions
and opinions about the practicality and cost of culling. Unlike
the scientific data, these sections of the report and their interpretation
have not been peer reviewed. In advising on whether or not culling
of badgers might be a policy option for the control of TB in cattle,
I would therefore urge you to acknowledge that the scientific
data support culling, but that the issues of cost and practicality
require more comprehensive and considered assessment than the
ISG gave them.
John and I also disagree on whether increased
cattle controls alone can bring TB in cattle under control. John
believes they can, partly on the basis of a simplified mathematical
model (Cox et al, 2005)5 but also because he overstates
the contribution that cattle movements make to the incidence of
TB in cattle. I remain of the view that even though TB control
by cattle-only measures could have an impact, control which includes
measures aimed at tackling the reservoir of infection in badgers
will be more rapid and more effective. Given the ISG's very clear
conclusion that badger-to-cattle transmission is the major contributor
to herd breakdowns, I would ask you to consider whether it is
realistic or reasonable to rely on cattle controls alone.
I am disappointed that the scientific evidence
presented within the main body of the ISG final report which supports
the conclusion that culling could be beneficial was not reflected
in the Chairman's statement in his overview of the ISG's final
report "that badger culling cannot meaningfully contribute
to the future control of cattle TB in Britain". I am also
disappointed that some of his subsequent comments may have misrepresented
the situation. Examples are included in my comments, attached,[14]
on the more detailed points made by the former members of the
ISG and Professor Denis Mollison.
References
1 Godfray HCJ, Curnow RN, Dye C, Pfeiffer D,
Sutherland WJ and Woolhouse MEJ. (2004) Independent scientific
review of the Randomised Badger Culling Trial and associated epidemiological
research.
2 More SJ, Clegg TA, McGrath G, Collins JD, Corner
LA, Gormley E (2007) Does reactive badger culling lead to an increase
in tuberculosis in cattle? The Veterinary Record 161(6): 208-9.
3 Donnelly CA, Wei G, Johnston WT, Cox DR, Woodroffe
R, Bourne FJ, Cheeseman CL, Clifton-Hadley RS, Gettinby G, Gilks
P, Jenkins HE, Le Fevre AM, McInerney JP, Morrison WI. (2007)
Impacts of widespread badger culling on cattle tuberculosis: concluding
analyses from a large-scale field trial. International Journal
of Infectious Diseases 11(4): 300-8.
4 Donnelly CA, Woodroffe R, Cox DR, Bourne FJ,
Cheeseman CL, Clifton-Hadley RS, Wei G, Gettinby G, Gilks P, Jenkins
H, Johnston WT, Le Fevre AM, McInerney JP, Morrison WI (2006)
Positive and negative effects of widespread badger culling on
tuberculosis in cattle. Nature 439(7078): 843-6.
5 Cox DR, Donnelly CA, Bourne JF, Gettinby G,
McInerney JP, Morrison WI and Woodroffe R (2005) Simple model
for tuberculosis in cattle and badgers. Proceedings of the National
Academy of Sciences, USA 102(49): 17588-93. http://www.pnas.org/cgi/content/full/102/49/17588
14 Not printed. Back
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