Abstract

The incidence of bovine tuberculosis in cattle herds in GB has increased by 18% on average per year since the mid-1980s and bTB carries a high economic impact in GB with approximately £80 million being spent in 2006-7 on disease control. Many studies have been undertaken to try to identify risk factors for bTB herd breakdowns, though few have looked at risk factors for persistence of herd breakdowns. These herds are of particular interest since by failing to clear infection (‘prolonged’ breakdowns), or by having persistence of undetected infection or an increased likelihood of re-infection (‘recurrent’ breakdowns), they may act as a focus of infection.

Data available from a detailed herd-level case-control study have been analysed to assess the impact of herd-level management characteristics on the incidence of ‘prolonged’ bTB breakdowns. A novel approach has been taken re-classifying the original breakdown herds into ‘prolonged’ and ‘non-prolonged’ breakdowns, analysed by a logistic regression model in order to quantify the effect of different risk factors. The preliminary model has shown excellent discriminatory power when tested on the dataset used to form the model and is currently being tested on independent datasets to assess its predictive ability. Identification of risk factors together with this ability to predict which herds are more likely to suffer a prolonged breakdown in the future could be a valuable tool for Defra, particularly in terms of altering the management of these herds. It is hoped that the findings from this work will further the understanding of persistence of bTB that occurs in some herds in GB and contribute to improving current control policies.