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Evaluating evidence of association of bovine tuberculosis in cattle
and badgers
Journal
Journal of Applied Ecology Published Online: 11Sep2008
Authors
Jim Hone 1* and Christl A. Donnelly 2 1 Institute
for Applied Ecology, University of Canberra, Canberra 2601 Australia; and
2 MRC Centre for Outbreak Analysis and Modelling, Department of
Infectious Disease Epidemiology, Division of Epidemiology, Public Health
and Primary Care, Faculty of Medicine, Imperial College London, St Mary's
Campus, Norfolk Place, London W2 1PG UK
Abstract
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Bovine tuberculosis (TB) occurs in cattle and
badgers in the UK and control efforts are undertaken to reduce the
spread of the disease.
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This study evaluates relationships predicted by
nine epidemiological two-host models of disease spread generated by
various combinations of density-dependent, frequency-dependent and
environmental pathogen transmission. The relationships of interest are
between measures of TB in cattle and in badgers from 10 sites which
were randomly selected to be proactive badger culling sites in the UK
Randomized Badger Culling Trial. The data are from the initial badger
cull only.
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There was most support (Akaike weight=0·562,
R2=0·869) for models that predicted a positive linear relationship
between density of infectious cattle per square kilometre and the
density index of infectious badgers. There was less support (Akaike
weight=0·060) for a model that predicted a positive linear
relationship between density of infectious cattle per square kilometre
and the proportion of badgers infectious with Mycobacterium bovis. A
correction to reduce effects of badger carcase storage and an
examination of effects of the 2001 foot-and-mouth disease epidemic had
little impact on estimated relationships.
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Synthesis and applications. The results provide
support for two-host disease models of TB in cattle and wildlife such
as badgers, although the form of disease transmission cannot be
identified clearly by these analyses. The implication of the results
is that the best-fitting models predict that, in the absence of
intervention-related changes in badger behaviour, a reduction in
density of infectious badgers should reduce the density of infectious
cattle. However, analysis of bait-marking data collected following
experimental badger culls indicated that culling badgers profoundly
alters their spatial organization as well as their population density,
potentially influencing contact rates. Effective vaccination of
badgers, were it to become available, would be expected to reduce the
density of infectious badgers without directly affecting their
behaviour.
Keywords
badger • bovine tuberculosis • cattle • host–disease
model • multi-host disease models
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