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Subthreshold and superthreshold coexistence of pathogen variants: the impact of host age-structure

Maia Martcheva1, Sergei S Pilyugin, Robert D Holt

  • 1Department of Mathematics, University of Florida, 358 Little Hall, PO Box 118105, Gainesville, FL 32611-8105, USA. maia@math.ufl.edu

Mathematical Biosciences
|November 8, 2006
PubMed

Insights

Host age structure can enable multiple microparasite strains to coexist, even when competitive exclusion would normally occur. This occurs in basic models with frequency-dependent transmission and at least one virulent strain.

Area of Science:

  • Epidemiology
  • Mathematical Biology
  • Population Dynamics

Background:

  • Competitive exclusion principle typically limits pathogen variants to one dominant strain.
  • Super-infection, coinfection, and cross-immunity can allow pathogen polymorphism.
  • Host age-related infectivity can destabilize endemic equilibria, causing oscillations.

Purpose of the Study:

  • To investigate how host chronological age influences microparasite coexistence in basic epidemic models.
  • To explore the emergence of subthreshold dominance and coexistence equilibria due to age structure.
  • To determine conditions under which age structure facilitates pathogen coexistence.

Main Methods:

  • Mathematical modeling of microparasite dynamics incorporating host age structure.
  • Analysis of frequency-dependent transmission (proportionate mixing).
  • Examination of subthreshold equilibria and conditions for pathogen persistence.

Main Results:

  • Host age structure can drive coexistence of competing microparasites, overriding competitive exclusion.
  • Age structure leads to multiple subthreshold dominance and coexistence equilibria (weak and strong).
  • Coexistence is facilitated if at least one strain is virulent and can persist subthreshold, with the second strain having lower virulence.

Conclusions:

  • Host age structure is a critical factor promoting pathogen diversity in simple epidemic models.
  • Frequency-dependent transmission combined with age structure allows for novel coexistence mechanisms.
  • Virulence and subthreshold persistence mediated by age structure are key to understanding pathogen coexistence.

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