Date on Master's Thesis/Doctoral Dissertation


Document Type

Doctoral Dissertation

Degree Name

Ph. D.



Degree Program

Biology, PhD

Committee Chair

Ewald, Pual

Committee Co-Chair (if applicable)

Yanoviak, Stephen

Committee Member

Yanoviak, Stephen

Committee Member

Ewald, Holly

Committee Member

Dugatkin, Le

Committee Member

Crespo, Fabian

Author's Keywords

Chlamydia trachomatis; SARS-CoV-2; Plasmodium, virulence, evolution, transmission


Principles of natural selection have proven valuable for explaining why pathogens cause the diseases that they do. In theory, the evolved level of host exploitation should reflect how dependent a pathogen is on host health for transmission. This dependency is shaped by transmission mode and transmission opportunity, which should therefore be predictors of disease manifestations. In this dissertation, I apply these principles to investigations of depression in Chlamydia trachomatis and virulence of SARS-COV-2 and Plasmodium species. This dissertation has five chapters. In chapter I, I describe the theoretical foundation of my dissertation research. I also briefly introduce each study system. In chapter II, I evaluate whether C. trachomatis is associated with depression based on a candidate mechanism for within-host persistence. I hypothesize that C. trachomatis should be associated with depression independent of urogenital symptoms, and that the effect should be stronger in females than in males. In chapter III, I assess evolutionary trends in SARS-CoV-2’s virulence and viral loads by conducting meta-analyses of published results. From the evolutionary perspective that virulence of respiratory pathogens should correlate positively with environmental survivability, I hypothesize a trend of reduced virulence. In chapter IV, I qualitatively review epidemiological factors that may affect malaria severity and critically evaluate the hypothesis that virulence evolves as a function of transmission intensity. In chapter IV, I summarize the main findings and conclusions from chapters II through IV. I also discuss future research directions and potential applications.

Included in

Biology Commons