Maternal antibodies and density dependence affect suppression of host populations by novel pathogens

Current theory for the regulation of host populations by pathogens suggests that a high level of suppression during the initial epidemic phase will be followed by a population rebound with decreased virulence due to pathogen and host evolution, and the extent of host suppression increases with increasing pathogen transmissibility ( R ₀ ) and virulence. Using simple epidemiological models, we explore the effect of two factors on short- and long-term suppression: the strength of density-dependent population regulation (homeostasis) and maternal antibodies. We showed previously that, in the absence of maternal antibodies, the strength of homeostasis can greatly effect long term population suppression. Here we find that maternal antibodies can significantly reduce suppression of the host population if they attenuate rather than block infections, but then only for rapid homeostasis. A higher R ₀ can result in lower suppression, and the average virulence can decline over time without any (genetic) evolution. Our results suggest the need for a nuanced view of long-term suppression by a new pathogen, with the outcome sensitive to many details even in the absence of evolution.