Data from: Within-host competition in genetically diverse malaria infections: parasite virulence and competitive success.

Humans and animals often become coinfected with pathogen strains that
differ in virulence. The ensuing interaction between these strains can, in
theory, be a major determinant of the direction of selection on virulence
genes in pathogen populations. Many mathematical analyses of this assume
that virulent pathogen lineages have a competitive advantage within
coinfected hosts and thus predict that pathogens will evolve to become
more virulent where genetically diverse infections are common. Although
the implications of these studies are relevant to both fundamental biology
and medical science, direct empirical tests for relationships between
virulence and competitive ability are lacking. Here we use newly developed
strain-specific real-time quantitative polymerase chain reaction protocols
to determine the pairwise competitiveness of genetically divergent
Plasmodium chabaudi clones that represent a wide range of innate
virulences in their rodent host. We found that even against their
background of widely varying genotypic and antigenic properties, virulent
clones had a competitive advantage in the acute phase of mixed infections.
The more virulent a clone was relative to its competitor, the less it
suffered from competition. This result confirms our earlier work with
parasite lines derived from a single clonal lineage by serial passage and
supports the virulence-competitive ability assumption of many theoretical
models. To the extent that our rodent model captures the essence of the
natural history of malaria parasites, public health interventions which
reduce the incidence of mixed malaria infections should have beneficial
consequences by reducing the selection for high virulence.