R₀: Host Longevity Matters

Area of Science:

• Epidemiology and evolutionary biology
• Mathematical modeling of infectious diseases

Background:

• The basic reproduction ratio (R₀) is crucial for understanding epidemic spread.
• R₀ traditionally assumes a fully susceptible population and doesn't always account for host lifespan.
• Pathogen evolution is driven by optimizing within-host replication and mutation rates.

Purpose of the Study:

• To investigate how host longevity influences the basic reproduction ratio (R₀).
• To determine the optimal pathogen evolutionary strategy (replication vs. mutation rates) considering host lifespan.
• To identify conditions favoring 'killer' (rapid, short-term) versus 'milker' (slow, long-term) pathogen strategies.

Main Methods:

• Combined a generic within- and between-host epidemiological model.
• Analyzed the R₀ indicator as a function of pathogen replication and mutation rates.
• Investigated the impact of host longevity and host contact rates on pathogen strategy.

Main Results:

• Host longevity significantly impacts R₀, especially for long-lived hosts and long-lasting infections.
• Optimal pathogen strategy ([Formula: see text]) is influenced by host longevity and contact rate.
• A bifurcation line was identified, separating 'killer' and 'milker' strategies based on host longevity and contact rate.

Conclusions:

• For short host lifespans, a 'killer' strategy (high replication, short duration) is evolutionarily optimal.
• For very long host lifespans, a 'milker' strategy (slow, sustained replication) is advantageous.
• Intermediate host lifespans require considering the contact rate to determine the optimal pathogen strategy.