Spatial structure, host heterogeneity and parasite virulence: implications for vaccine‐driven evolution

Abstract

Natural host-parasite interactions exhibit considerable variation in host quality, with profound consequences for disease ecology and evolution. For instance, treatments (such as vaccination) may select for more transmissible or virulent strains. Previous theory has addressed the ecological and evolutionary impact of host heterogeneity under the assumption that hosts and parasites disperse globally. Here, we investigate the joint effects of host heterogeneity and local dispersal on the evolution of parasite life-history traits. We first formalise a general theoretical framework combining variation in host quality and spatial structure. We then apply this model to the specific problem of parasite evolution following vaccination. We show that, depending on the type of vaccine, spatial structure may select for higher or lower virulence compared to the predictions of non-spatial theory. We discuss the implications of our results for disease management, and their broader fundamental relevance for other causes of host heterogeneity in nature.

Epidemiological and evolutionary consequences of periodicity in treatment coverage

“…However, if the pathogen adapts to the bad habitat by increasing its virulence, this can negatively impact untreated hosts in the population. The potential negative effects of such imperfect treatments have been theoretically studied, showing in particular that some types of treatments (notably those reducing host susceptibility or pathogen transmissibility) can be viewed as evolution-proof, while others (such as those that mainly increase the tolerance of hosts to the disease) can lead to the long-term evolution of virulence [7][8][9].…”

“…Our purpose here is to analyse the epidemiological and evolutionary effects of periodic imperfect prophylactic treatments that create heterogeneity among hosts. Building on previous theoretical studies of imperfect treatments with constant coverage [7][8][9], we first present the consequences of periodic treatment coverage on the prevalence of the disease and the pathogen's basic reproduction number. We then assume that a rare mutation occurs in the pathogen, modifying the life-history traits, and we analyse how the selective pressures on the mutant pathogen depend on (i) the mode of action, and (ii) the temporal distribution of treatments.…”

The evolution of stage-specific virulence: differential selection of parasites in juveniles

“…Therefore, sources of heterogeneity in hosts can lead to different predictions than classic virulence evolution theory based on the marginal value theorem, as claimed in a recent conceptual review (Lion & Metz 2018). Our novel results arise because we explicitly assumed stage-structure with maturation from juveniles to adults and reproduction by adults, rather than more generic host heterogeneity, e.g., multiple host species (Regoes et al 2000;Gandon 2004;Osnas & Dobson 2011), vaccination (Gandon et al 2001;Gandon et al 2003;Yates et al 2006;Zurita-Gutiérrez & Lion 2015), or sex (Úbeda & Jansen 2016).…”

The evolution of stage-specific virulence: Differential selection of parasites in juveniles

“…This is an example where sources of heterogeneity in hosts can lead to different predictions than classic virulence evolution theory based on the optimization principle (Lion and Metz ). Our novel results arise because we explicitly assumed stage structure with maturation from juveniles to adults and reproduction by adults, rather than more generic host heterogeneity, for example, multiple host species (Regoes et al ; Gandon ; Osnas and Dobson ), vaccination (Gandon et al , ; Yates et al ; Zurita‐Gutiérrez and Lion ), or sex (Úbeda and Jansen ).…”