Fig 2. Combining the epidemiology and evolution of infectious diseases.

(A) Evolutionary rescue of a parasite population via mutation, (B) representation of the SI epidemiological model, and (C) virulence evolution in response to different types of interventions. In panel A, the resident strain (in black) cannot generate a large outbreak (its R₀ < 1), but it can still persist long enough for a mutation event to occur that can lead to a well-adapted mutant (in red) [26]. In panel C, the predictions are obtained using the Price equation formalism and the assumptions from Fig 2 in [30]. The colour of the curves corresponds to the arrows in panel B (black is the untreated case). Even in absence of treatment, the virulence evolves in the short term because its initial value is far from its optimal value. The virulence-blocking treatment (in yellow) leads to the highest increase virulence, whereas the treatment-blocking (in green) first favours less virulent strains. Increasing host recovery rate (in grey) also increases virulence. SI, Susceptible-Infected.