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Open Access Research article

Impact of external sources of infection on the dynamics of bovine tuberculosis in modelled badger populations

Joanne L Hardstaff1, Mark T Bulling14, Glenn Marion2, Michael R Hutchings3 and Piran C L White1*

Author Affiliations

1 Environment Department, University of York, York, YO10 5DD, UK

2 Biomathematics and Statistics Scotland, James Clerk Maxwell Building, Kings Buildings, Edinburgh, EH9 3HH, UK

3 Disease Systems, Scottish Agricultural College, West Mains Road, Edinburgh, EH9 3JG, UK

4 Biological Sciences, University of Derby, Kedleston Road, Derby, DE22 1 GB, UK

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BMC Veterinary Research 2012, 8:92  doi:10.1186/1746-6148-8-92

Published: 27 June 2012

Abstract

Background

The persistence of bovine TB (bTB) in various countries throughout the world is enhanced by the existence of wildlife hosts for the infection. In Britain and Ireland, the principal wildlife host for bTB is the badger (Meles meles). The objective of our study was to examine the dynamics of bTB in badgers in relation to both badger-derived infection from within the population and externally-derived, trickle-type, infection, such as could occur from other species or environmental sources, using a spatial stochastic simulation model.

Results

The presence of external sources of infection can increase mean prevalence and reduce the threshold group size for disease persistence. Above the threshold equilibrium group size of 6–8 individuals predicted by the model for bTB persistence in badgers based on internal infection alone, external sources of infection have relatively little impact on the persistence or level of disease. However, within a critical range of group sizes just below this threshold level, external infection becomes much more important in determining disease dynamics. Within this critical range, external infection increases the ratio of intra- to inter-group infections due to the greater probability of external infections entering fully-susceptible groups. The effect is to enable bTB persistence and increase bTB prevalence in badger populations which would not be able to maintain bTB based on internal infection alone.

Conclusions

External sources of bTB infection can contribute to the persistence of bTB in badger populations. In high-density badger populations, internal badger-derived infections occur at a sufficient rate that the additional effect of external sources in exacerbating disease is minimal. However, in lower-density populations, external sources of infection are much more important in enhancing bTB prevalence and persistence. In such circumstances, it is particularly important that control strategies to reduce bTB in badgers include efforts to minimise such external sources of infection.

Keywords:
Cattle; Disease; Host community; Model; Threshold; Perturbation