Date on Master's Thesis/Doctoral Dissertation

5-2023

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biology

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

Abstract

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.

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