Detrimental effect of pathogen avoidance for non-lethal diseases.

<p>It is represented by the relative frequency (<i>r</i>, Y-axis) at which “avoider” individuals suffer classical infections compared to “normal” ones (when values are below one, avoiding the pathogenic agent is beneficial), according to the rate of infection by a pathogenic agent (X-axis). (A) For total immune periods of one year, avoiding the pathogenic agent is beneficial only for low infection rates. For high infection rates, both strategies tend to become equivalent since boosts to the immune system are almost systematic; (B) for lifelong immunity, avoiding the pathogenic agent is always a good strategy; and (C) considering a continuum in the total duration of immunity (in years) shows that “avoiders” can be more than six times more at risk of becoming sick compared to “normal” individuals. The threshold where both strategies are equivalent (<i>r</i> = 1) is represented with a dashed line (A) or with a bold red line (C).