Eco-evolutionary dynamics of adapting pathogens and host immunity.

Area of Science:

• Epidemiology
• Viral Evolution
• Immunology

Background:

• Pathogen spread depletes susceptible hosts and builds immunity, creating selective pressure for viral evolution.
• RNA viruses like influenza and SARS-CoV-2 rapidly evolve immune-evasive variants.
• Host immunity wanes, limiting the growth advantage of escape variants.

Purpose of the Study:

• To model the eco-evolutionary dynamics between evolving viruses and dynamic host immunity.
• To investigate how host-pathogen interactions shape viral adaptation.
• To explain the quasi-neutral dynamics of high-frequency variants in light of adaptive evolution.

Main Methods:

• Utilized a Susceptible/Infected (SI) model.
• Simulated interactions between an evolving viral population and an immunologically diverse host population.
• Analyzed variant growth dynamics under varying conditions of cross-immunity, host heterogeneity, and immune response durability.

Main Results:

• Escape variants initially show exponential growth but lose advantage before high frequencies.
• Variant trajectories become unpredictable, resembling an anomalous random walk influenced by future variants.
• Model explains the paradox of adaptive viral evolution alongside quasi-neutral high-frequency variant dynamics.

Conclusions:

• Viral adaptation is shaped by eco-evolutionary interactions, not just rapid evolution in a fixed environment.
• The interplay between viral escape and host immunity dynamics is crucial for understanding pathogen evolution.
• The model provides a framework for understanding complex variant dynamics observed in human RNA viruses.