title: Coinfection and the evolution of parasite virulence.
abstract: Analyses of the selection pressures acting on parasite virulence are made more complicated when individual hosts can simultaneously harbour many different strains or genotypes of a parasite. Here we explore the evolutionary dynamics of host-parasite associations in which individual hosts can be coinfected with many different parasite strains. (We take coinfection to mean that each strain transmits at a rate unaffected by the presence of others in the same host.) This study thus represents the opposite extreme to our earlier work on superinfection in which there is a dominance hierarchy such that only the most virulent strain present in a host is transmitted. For highly diverse populations of parasite strains, we find that such coinfection leads to selection for strains whose virulence-levels lie in a relatively narrow band close to the maximum consistent with the parasite's basic preproductive ratio, R0, exceeding unity.
authors.affiliation: Department of Zoology, University of Oxford, U.K.
authors.forename: R M
authors.initials: RM
authors.lastname: May
authors.forename: M A
authors.initials: MA
authors.lastname: Nowak
mesh_terms: D000818:Animals; D005075:Biological Evolution; D006790:Host-Parasite Interactions / Q000235:genetics; D008433:Mathematics; D008954:Models, Biological; D010271:Parasites / Q000235:genetics / Q000472:pathogenicity*; D010272:Parasitic Diseases / Q000469:parasitology / Q000635:transmission; D014774:Virulence