Superinfections can induce evolutionarily stable coexistence of pathogens

Area of Science:

• Evolutionary biology
• Parasitology
• Mathematical modeling

Background:

• Parasite reproduction and natural selection occur at multiple interconnected levels.
• Previous work linked between-host transmission (SI model) to within-host dynamics, showing potential divergence in selection outcomes.
• Understanding the interplay between within-host and population-level selection is crucial for parasite evolution.

Purpose of the Study:

• To investigate the evolution of parasite reproduction rate considering superinfection.
• To model the probability of a new parasite strain taking over an already infected host.
• To analyze how different mathematical properties of superinfection functions affect evolutionary outcomes.

Main Methods:

• Introduction of a superinfection function, phi(p,q), representing takeover probability.
• Analysis of three cases based on the mathematical properties (discontinuity, continuity, differentiability) of the superinfection function.
• Integration of within-host dynamics with between-host transmission models.

Main Results:

• Case (i): Discontinuous superinfection function leads to within-host selection dominating evolutionary outcomes.
• Case (iii): Differentiable superinfection function results in transmission to susceptible hosts dominating, aligning with models ignoring superinfection.
• Case (ii): Continuous, non-differentiable superinfection function (biologically relevant) shows contributions from both reproduction levels.
• Superinfection models can allow for stable coexistence of parasite traits.

Conclusions:

• The mathematical nature of superinfection probability critically shapes parasite evolution.
• Superinfection can lead to novel evolutionary stable strategies and coexistence of parasite types.
• The study provides a framework for understanding complex parasite evolution incorporating superinfection.