Abstract
BackgroundBadgers are involved in the transmission to cattle of bovine tuberculosis (TB), a serious problem for the UK farming industry. Cross-sectional studies have shown an association between bite wounds and TB infection in badgers which may have implications for M. bovis transmission and control, although the sequence of these two events is unclear. Transmission during aggressive encounters could potentially reduce the effectiveness of policies which increase the average range of a badger and thus its opportunities for interaction with other social groups.MethodsData were obtained on badgers captured during a long term study at Woodchester Park, UK (1998–2006). Many badgers had multiple observations. At each observation, the badger was assigned a “state” depending on presence of bite wounds and/or TB infection. Hence each badger had a “transition” from the previous state to the current state. We calculated the numbers of each type of transition and the time spent in each state. Transition rates were calculated for each transition category, dividing the number of such transitions by the total time at risk. We compared the rate of bite wound acquisition in infected badgers with that for uninfected badgers and the rate of positive M.bovis test results in bitten badgers with that in unbitten badgers.ResultsThe rate of bite wound acquisition in infected badgers (0.291 per year) was 2.09 (95% CI: 1.41, 3.08) times that in uninfected badgers (0.139 per year). The rate of positive M.bovis test results in bitten badgers (0.097 per year) was 2.45 (95% CI: 1.29, 4.65) times that in unbitten badgers (0.040 per year).ConclusionsWe found strong evidence of both potential sequences of events consistent with transmission via bite wounds and distinctive behaviour in infected badgers. The complex relationship between behaviour and infection must be considered when planning TB control strategies.
Highlights
Bovine tuberculosis (TB) is a serious problem for cattle farmers in the U.K. and Republic of Ireland [1,2]
The maximum number of observations for a single badger was 28, and the median was 3. Of those animals included in the analysis, 21.8% were detected as culture positive by clinical sampling, 27.5% at some point yielded a positive ELISA test result and 53.0% were observed with a bite wound at some point
Our study demonstrates that the association between bite wounding and the progression of TB infection in badgers can potentially be explained by both sequences of events: advanced disease is significantly more likely to occur in bitten badgers whilst animals with advanced disease are significantly more likely to be bitten
Summary
Bovine tuberculosis (TB) is a serious problem for cattle farmers in the U.K. and Republic of Ireland [1,2]. There is evidence of an association between bite wounds and M.bovis infection [11,13,14], implying an additional process that could be occurring alongside aerosol transmission. This additional hypothesis is that TB infected badgers may be more likely to be bitten. Previous work has shown that management interventions can have profound effects on the social behavior of badger populations [6], and potentially on rates of bite wounding. Cross-sectional studies have shown an association between bite wounds and TB infection in badgers which may have implications for M. bovis transmission and control, the sequence of these two events is unclear. Transmission during aggressive encounters could potentially reduce the effectiveness of policies which increase the average range of a badger and its opportunities for interaction with other social groups
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