Evolutionary invasion analysis of modern epidemics highlights the context-dependence of virulence evolution
by Sudam Surasinghe, Ketty Kabengele, Paul E. Turner, C. Brandon Ogbunugafor
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Why do some pathogens evolve to make their hosts more sick, and others less? This characteristic is embodied in the concept of “virulence,” a central idea in infectious diseases that describes the harm that a pathogen inflicts upon a host. Examining how virulence evolves constitutes a subfield of evolutionary theory, that attempts to make concrete predictions for how we should expect infectious diseases to evolve. In this study, we construct models of various epidemics, and apply a set of mathematical methods based on game theory that identify characteristics of mutant pathogens that render them uninvadable (that is, they cannot be invaded and replaced by a different strain of pathogen). We demonstrate that pathogens that are spread via different routes—“directly” (as in SARS-CoV-2) or “indirectly” as in diseases like hepatitis C virus in a population of persons who inject drugs—have profoundly different expectations for how. Our findings have implications for how we analyze and prevent modern epidemics. We learn that how virulence will evolve is context-dependent. Consequently, our predictive models of the evolution of virulence should be tailor made to fit the particulars of certain infectious diseases.
A diagram of an infectious disease model with multiple evolved strains of a pathogen.
