Continuously stable strategy of pathogen evolution in a classic epidemiological SIR model

07 March 2019

Using the framework of adaptive dynamics, here a classic susceptible-infected-recovery (SIR) host- pathogen model was considered to explore the evolutionary dynamics of pathogen virulence. Both transmission rate and recovery rate were assumed to be constrained by trade-offs with the pathogenic virulence, and the trade-offs crucially determined the behavior of the evolutionary dynamics. No additional increase in mortality due to infection was assumed and the invasion fitness and evolutionary trajectories of pathogen virulence were explored using pairwise invadability plots. The results showed that initial strains of viruses with different levels of virulence converged to one continuously stable singular point, prohibiting any other complex evolutionary outcomes to occur on the strain diversity. The insufficient nonlinearity in the population dynamics and the lack of additional increase of mortality due to infection could have led to the lack of evolutionary diversity, which could, nonetheless, serve as the base for developing potential mechanisms for reducing the diversity of virus strains in public health management.