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Integrating Infection Intensity into Within- and Between-Host Pathogen Dynamics: Implications for Invasion and
Abstract:
AbstractInfection intensity can dictate disease outcomes but is typically ignored when modeling infection dynamics of microparasites (e.g., bacteria, virus, and fungi). However, for a number of pathogens of wildlife typically categorized as microparasites, accounting for infection intensity and within-host infection processes is critical for predicting population-level responses to pathogen invasion. Here, we develop a modeling framework we refer to as reduced-dimension host-parasite integral projection models (reduced IPMs) that we use to explore how within-host infection processes affect the dynamics of pathogen invasion and virulence evolution. We find that individual-level heterogeneity in pathogen load-a nearly ubiquitous characteristic of host-parasite interactions that is rarely considered in models of microparasites-generally reduces pathogen invasion probability and dampens virulence-transmission trade-offs in host-parasite systems. The latter effect likely contributes to widely predicted virulence-transmission trade-offs being difficult to observe empirically. Moreover, our analyses show that intensity-dependent host mortality does not always induce a virulence-transmission trade-off, and systems with steeper than linear relationships between pathogen intensity and host mortality rate are significantly more likely to exhibit these trade-offs. Overall, reduced IPMs provide a useful framework to expand our theoretical and data-driven understanding of how within-host processes affect population-level disease dynamics.
Insights
Accounting for infection intensity in microparasite models is crucial. Heterogeneity in pathogen load typically reduces invasion probability and dampens virulence-transmission trade-offs, impacting disease dynamics.
Area of Science:
- Ecology
- Epidemiology
- Mathematical Biology
Background:
- Infection intensity is often overlooked in microparasite (e.g., bacteria, viruses, fungi) dynamics modeling.
- Understanding within-host pathogen processes is vital for predicting population-level responses to invasions, especially in wildlife.
- Existing models frequently simplify host-parasite interactions by not accounting for individual variation in pathogen load.
Purpose of the Study:
- To develop and apply a novel modeling framework, reduced-dimension host-parasite integral projection models (reduced IPMs).
- To investigate how within-host infection intensity influences pathogen invasion dynamics.
- To explore the evolution of virulence and its relationship with transmission in host-parasite systems.
Main Methods:
- Development of reduced-dimension host-parasite integral projection models (reduced IPMs).
- Simulation and analysis of host-parasite interactions incorporating infection intensity.
- Exploration of the relationship between pathogen load, host mortality, and transmission rates.
Main Results:
- Individual-level heterogeneity in pathogen load generally decreases pathogen invasion probability.
- Varying pathogen loads dampen the predicted virulence-transmission trade-offs, potentially explaining empirical difficulties in observing them.
- Intensity-dependent host mortality does not always result in a virulence-transmission trade-off; steeper relationships increase the likelihood of observing trade-offs.
Conclusions:
- Reduced IPMs offer a powerful framework for integrating within-host processes into population-level disease dynamics.
- Host-parasite interactions are significantly shaped by variation in pathogen load, affecting invasion and virulence.
- The study highlights the importance of considering infection intensity for a more accurate understanding of disease ecology and evolution.
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