This research builds on field and laboratory work investigating the prevalence of multiple trypanosome infections in the Serengeti by experimentally addressing a central question of disease evolution. Theory predicts that competition among different parasites in one host animal will lead to increased severity (virulence) of each parasite, but empirical support for this prediction is scarce. To test the prediction, mice will be infected with different strains of Trypanosoma brucei, protozoan parasites of great economic and medical importance. Three parasite strains, visually distinguishable by different fluorescent markers introduced into their genomes, will be repeatedly passed through mice alone or in combinations. Parasites will then be isolated from mixed infections and their effect on mice will be measured to determine whether they have evolved to higher virulence than the same parasites in single infections, as theory would predict. The intellectual merit of the proposed experiment is to provide for a critical test of the effect of multiple infections on parasite virulence. The resulting empirical data will help put virulence evolution theory on a better foundation. The proposed research will have broader impact by improving our understanding of parasite and disease dynamics. As an international collaboration it will also transfer knowledge among institutions in the United States, Europe, and Africa.
