Résumé
Parasite evolution is a major public health issue. The aim of this thesis is to understand micro-parasite virulence evolution through a theoretical approach based on within-host models linked to an epidemiological framework (also called embedded models). The host’s immune response exerts a major selection pressure on parasite virulence. In parasitology, most within-host models incorporate the immune system as a dynamical system, but in these models, the outcome of the infection generally is an a priori assumption. Nevertheless, these models offer new perspectives to study virulence evolution. Most studies assume that a parasite cannot increase its transmission rate without causing more harm to its host. However, the existence of such a trade-off relationship between transmission and virulence has been challenged. Using an embedded model, we study how a trade-off can emerge and what its characteristics are. Applying this framework to the case of vector-borne parasites, we work out how specific aspects of the parasites and interaction with its host affect the trade-off. Finally, we investigate the consequences of multiple infections on virulence evolution. The results of our study have public health implications as our models allow to predict possible consequences of anti-parasite treatments on virulence evolution. We suggest it would be reasonable to take these effects into account when elaborating public health policies to avoid an “arms race” between hosts and parasites.