COS 282-2 - Effects of transgenerational virulence on host-pathogen dynamics

Abstract: Understanding the population-level consequences of host-pathogen interactions is important for predicting how outbreaks will affect host population dynamics. An obvious driver of these population-level effects is the reduction in fitness of individuals who have been infected by the pathogen. However, recent work on a microsporidian pathogen of Daphnia shows that the pathogen reduces the fitness of not only the infected individual, but also the fitness of the infected individual’s offspring, even though the offspring were never infected. The goal of this study is to explore how this transgenerational virulence (i.e., the reduced fitness of offspring of infected individuals) affects disease levels and population densities of the host population. Our approach was to develop an environmental transmission SIR-type model, which divides the host population into susceptible individuals, infected individuals, and the offspring of infected individuals (called “compromised” individuals). We used the model to explore how increased mortality rates, reduced reproduction rates, and increased infection rates of compromised individuals affect the equilibrium total density, infection prevalence, and infected density of the host population. Our model predicts that in most scenarios (i) increased mortality of compromised individuals lowers total host density, but also lowers disease prevalence and infection density, (ii) decreased reproduction by compromised individuals lowers total host density, but also lowers infection prevalence and infected density, and (iii) increased transmission rates of compromised individuals lowers total host density and raises infection prevalence and infected density. Overall, our work shows that transgenerational virulence can have substantial effects on host population densities and infection levels.