Immunity Promotes Virulence Evolution in a Malaria Model
Margaret J. Mackinnon1* , Andrew F. Read1

1 School of Biological Sciences, University of Edinburgh, Edinburgh, United
Kingdom

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 ("naïve") mice using
serial passage. We found that parasite lines evolved in immunized mice
became more virulent to both naïve and immune mice than lines evolved in
naïve 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 naïve mice than the
naïve-selected lines, though not to immunized mice. Thus, immune selection
accelerated the rate of virulence evolution, rendering parasites more
dangerous to naïve hosts. These results argue for further consideration of
the evolutionary consequences for pathogen virulence of vaccination.

Full Text at
http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371%2Fjournal.pbio.0020230

Comment:
The development of natural immunity may lead to extra selection pressure
against those individuals not carrying or inheriting that immunity, thus
accelerating evolution of immunity.  If phenotypic traits accompanied that
immunity, such as those animals first having the immunity also having some
phenotypic variation, then the evolution of that variation will also be
accelerated - just a thought :)

Posted by
Robert Karl Stonjek
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