• Open Access

Evolution of virulence: triggering host inflammation allows invading pathogens to exclude competitors


  • Sam P. Brown,

    Corresponding author
    1. Section of Integrative Biology, University of Texas at Austin, Austin, TX 78712, USA
    2. Department of Zoology, University of Oxford, South Parks Rd, Oxford OX1 3PS, UK
      *Correspondence: E-mail: sam.brown@cantab.net
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  • Ludovic Le Chat,

    1. London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
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  • François Taddei

    1. University of Paris 5, Faculty of Medicine, INSERM, U571, 156 Rue de Vaugirard, F-75730 Paris 15, France
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  • Reuse of this article is permitted in accordance with the Creative Commons Deed, Attribution 2.5, which does not permit commercial exploitation.

*Correspondence: E-mail: sam.brown@cantab.net


Virulence is generally considered to benefit parasites by enhancing resource-transfer from host to pathogen. Here, we offer an alternative framework where virulent immune-provoking behaviours and enhanced immune resistance are joint tactics of invading pathogens to eliminate resident competitors (transferring resources from resident to invading pathogen). The pathogen wins by creating a novel immunological challenge to which it is already adapted. We analyse a general ecological model of ‘proactive invasion’ where invaders not adapted to a local environment can succeed by changing it to one where they are better adapted than residents. However, the two-trait nature of the ‘proactive’ strategy (provocation of, and adaptation to environmental change) presents an evolutionary conundrum, as neither trait alone is favoured in a homogenous host population. We show that this conundrum can be resolved by allowing for host heterogeneity. We relate our model to emerging empirical findings on immunological mediation of parasite competition.