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      Risk of tuberculosis cattle herd breakdowns in Ireland: effects of badger culling effort, density and historic large-scale interventions

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      Veterinary Research

      BioMed Central

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          Abstract

          Bovine tuberculosis (bTB) continues to be a problem in cattle herds in Ireland and Britain. It has been suggested that failure to eradicate this disease is related to the presence of a wildlife reservoir (the badger) . A large-scale project was undertaken in the Republic of Ireland during 1997–2002 to assess whether badger removal could contribute to reducing risk of cattle herd breakdowns in four areas. During the period of that “four area” study, there was a significant decrease in risk in intensively culled (removal) areas relative to reference areas. In the present study, we revisit these areas to assess if there were any residual area effects of this former intervention a decade on (2007–2012). Over the study period there was an overall declining trend in bTB breakdown risk to cattle herds. Cattle herds within former removal areas experienced significantly reduced risk of breakdown relative to herds within former reference areas or herds within non-treatment areas (OR: 0.53; P < 0.001). Increased herd breakdown risk was associated with increasing herd size (OR: 1.92-2.03; P < 0.001) and herd bTB history (OR: 2.25-2.40; P < 0.001). There was increased risk of herd breakdowns in areas with higher badger densities, but this association was only significant early in the study (PD*YEAR interaction; P < 0.001). Badgers were culled in areas with higher cattle bTB risk (targeted culling). Risk tended to decline with cumulative culling effort only in three counties, but increased in the fourth (Donegal). Culling badgers is not seen as a viable long-term strategy. However, mixed policy options with biosecurity and badger vaccination, may help in managing cattle breakdown risk.

          Electronic supplementary material

          The online version of this article (doi:10.1186/s13567-014-0109-4) contains supplementary material, which is available to authorized users.

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          Most cited references 35

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          Akaike's information criterion in generalized estimating equations.

           W. PAN-NGUM (2001)
          Correlated response data are common in biomedical studies. Regression analysis based on the generalized estimating equations (GEE) is an increasingly important method for such data. However, there seem to be few model-selection criteria available in GEE. The well-known Akaike Information Criterion (AIC) cannot be directly applied since AIC is based on maximum likelihood estimation while GEE is nonlikelihood based. We propose a modification to AIC, where the likelihood is replaced by the quasi-likelihood and a proper adjustment is made for the penalty term. Its performance is investigated through simulation studies. For illustration, the method is applied to a real data set.
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            The impact of badger removal on the control of tuberculosis in cattle herds in Ireland.

            In Ireland, the herd prevalence of bovine tuberculosis has remained stable for several decades, and in common with several other countries, progress towards eradication has stalled. There is evidence in support of the potential role of infected badgers (Meles meles, a protected species) in bovine tuberculosis in Ireland and Britain. However, this evidence on its own has not been sufficient to prove disease causation. Field trials are likely to offer the best opportunity to define this role. Building on the earlier East Offaly project, our objectives were to assess the impact of badger removal on the control of tuberculosis in cattle herds in Ireland. The study was conducted from September 1997 to August 2002 in matched removal and reference areas (average area of 245.1km(2)) in four counties: Cork, Donegal, Kilkenny and Monaghan. Badger removal was intensive and proactive throughout the study period in the removal areas, but reactive (in response to severe tuberculosis outbreaks in cattle) in the reference areas. Removal intensity in the removal and reference areas during the first 2 years of the study averaged 0.57 and 0.07 badgers/km(2)/year, respectively. The outcome of interest was restriction of cattle herds due to confirmed tuberculosis, where tuberculous lesions were detected in one or more animals. Data were analysed using logistic regression (modelling the probability of a confirmed herd restriction) and survival analysis (modelling time to a confirmed herd restriction). During the study period, there was a significant difference between the removal and reference areas in all four counties in both the probability of and the time to a confirmed herd restriction due to tuberculosis. In the final year of the study, the odds of a confirmed herd restriction in the removal (as compared to the reference areas) were 0.25 in Cork, 0.04 in Donegal, 0.26 in Kilkenny and 0.43 in Monaghan. Further, the hazard ratios (removal over reference) ranged from 0.4 to 0.04 (a 60-96% decrease in the rate at which herds were becoming the subject of a confirmed restriction).
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              Tuberculosis in badgers; a review of the disease and its significance for other animals.

              This review examines the current state of knowledge of aspects of tuberculosis in the badger. The gross pathology and pathogenesis are elaborated as well as the immune mechanism, diagnosis of infection and excretion and viability of infected products. The epidemiology in badgers is considered, as is the significance of infection in this species for other wildlife species as well as domestic animals sharing the same habitat. Trials of the effects of the removal of badgers on the occurrence of tuberculosis in cattle are summarised. It is concluded that badgers are well adapted as the primary host of bovine tuberculosis in parts of Britain and much of Ireland. Copyright 2000 Harcourt Publishers Ltd.
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                Author and article information

                Contributors
                ecologicalepidemiology@gmail.com
                paul.w.white@ucd.ie
                guy.mcgrath@ucd.ie
                james.okeeffe@agriculture.gov.ie
                swmartin@ovc.uoguelph.ca
                Journal
                Vet Res
                Vet. Res
                Veterinary Research
                BioMed Central (London )
                0928-4249
                1297-9716
                26 October 2014
                26 October 2014
                2014
                : 45
                : 1
                Affiliations
                [ ]Centre for Veterinary Epidemiology and Risk Analysis, School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland
                [ ]Current address: Veterinary Sciences Division, Bacteriology Branch, Agri-Food and Biosciences Institute, Stormont, Stoney Road, Belfast, BT4 3SD UK
                [ ]Department of Agriculture, Food, and the Marine, Agriculture House, Dublin 2, Ireland
                [ ]Department of Population Medicine, University of Guelph, Guelph, Canada
                Article
                109
                10.1186/s13567-014-0109-4
                4230509
                25344430
                © Byrne et al.; licensee BioMed Central Ltd. 2014

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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                Research
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                © The Author(s) 2014

                Veterinary medicine

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