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btb distances in East Offaly
Journal
Preventive
Veterinary Medicine - Vol
31, Iss 1-2 , July 1997, pp113-125
Authors
S. W. Martin, , J. A. Eves, L. A. Dolan, R. F. Hammond, J. M. Griffin, J. D. Collins and M. M. Shoukri
from University of Guelph, Canada and University College Dublin.
Abstract
The proximity of farms to badger setts was compared between farms that had
experienced a tuberculosis breakdown and those that had not, over the 6 year
period from 1988 to 1993. The data were derived from a badger removal study
conducted in East Offaly County in the Republic of Ireland. Badger removal began
in 1989 and continued through 1993; by the end of 1990, approximately 80% of all
badgers caught in the 6 year period had been removed. All badgers were examined,
grossly, for evidence of tuberculosis. Tuberculosis status of the approximately
900 study herds was based on the results of the single intradermal comparative
skin test and/or lesions of bovine tuberculosis. All herds were tested at least
once annually. The number of herds experiencing bovine tuberculosis declined
over the period, particularly in the years 1992 and 1993.
The data on farm and badger sett location were stored and analysed,
initially, in a geographical information system. Owing to the badger removal
programme, the distance between the barn yard of a typical farm and the nearest
occupied badger sett increased, by about 300 m year−1, and by about 600 m year−1
to the closest infected sett. In bivariate analyses, in the years 1988 and 1989,
the risk of tuberculosis declined with increasing distance to a badger sett
containing one or more tuberculous badgers. In multivariable logistic regression
analyses, year and the average number of cattle tested per farm per year were
controlled. A second identical analysis was conducted to control for the
repeated observations on the same herds using generalised estimating equations.
In both analyses, the risk of a multiple reactor tuberculosis breakdown
decreased for herds at least 1000 m away from an infected badger sett, and
increased as the number of infected badgers per infected sett increased. Despite
the significantly reduced risk of a breakdown with increasing distance to
infected badger setts, the relationship was not strong (sensitivity and
specificity of the model in the low 70% range) and explained only 9–19% of
tuberculosis breakdowns.
Keywords
Badger; Tuberculosis; Epidemiology; Bovine; Cattle;
Herd; Distance; Exposure; Etiologic fraction; Odds ratio; Logistic
regression; Generalised estimating equations
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