Immunity Promotes Virulence Evolution in a Malaria Model
Date
2004Author
Mackinnon, Margaret J
Read, Andrew F
Metadata
Abstract
Evolutionary models predict that host immunity will shape the evolution of parasite virulence. While some
assumptions of these models have been tested, the actual evolutionary outcome of immune selection on virulence has
not. Using the mouse malaria model, Plasmodium chabaudi, we experimentally tested whether immune pressure
promotes the evolution of more virulent pathogens by evolving parasite lines in immunized and nonimmunized
(‘‘naive’’) mice using serial passage. We found that parasite lines evolved in immunized mice became more virulent to
both naive and immune mice than lines evolved in naive mice. When these evolved lines were transmitted through
mosquitoes, there was a general reduction in virulence across all lines. However, the immune-selected lines remained
more virulent to naive mice than the naive-selected lines, though not to immunized mice. Thus, immune selection
accelerated the rate of virulence evolution, rendering parasites more dangerous to naı¨ve hosts. These results argue for
further consideration of the evolutionary consequences for pathogen virulence of vaccination.