Game dynamics as a driver for pathogen spillover pulses

Abstract

Understanding the underlying mechanisms for pathogen spillover is a main quest in epidemiology. Given the complexity of multi-host systems, several factors may play a relative role in spillover dynamics. A relatively less studied factor is the internal dynamics of pathogens that result from inter-strain competition. The competitive interactions among strains can cause deterministic changes in the population dynamics of pathogens. Such changes may affect the potential host-range of pathogens, influencing the probability of pathogen spillover. Here, our main goal is to show how an evolutionary game played by coexisting strains may induce pulses of pathogen spillover. To this end, we build a multi-host-multi-strain mean field model in which strains residing in a reservoir host have different capacities to explore an incidental host. We modelled inter-strain competition as a superinfection network and apply a game-theoretical analysis to it. The results indicate that game outcome depends on how reservoir hosts deal with the superinfection process (if superinfection is lethal, results in competitive exclusion or in coinfection). Our analysis suggests that game outcome can produce cycles in the strain composition that are cryptic in relation to the epidemiological dynamics of reservoirs (cycles in strain frequency composition cause small or no effect in the reservoir population). This suggests that relying solely on reservoir distribution and prevalence may subestimate the chance of pathogen spillover. Moreover, pulses of spillover can rely on the standing variation of pathogens, with no need for the emergence of novel mutations that increases pathogen host-range.