Sit-and-wait pathogens: Consequences of heterogeneity in pathogen exposure dynamics for environmentally persistent pathogens

Transmission is a fundamental component of host-pathogen systems. Despite complex biological processes interacting to determine whether a pathogen successfully infects a host, transmission parameters often assume a constant per-contact transmission probability. Factors that can influence risk of infection include the frequency of exposures, duration of a contact, and dose acquired during an interaction, which are collectively referred to as transmission determinants. These determinants of infection can vary among hosts and between routes of transmission (e.g. direct and indirect) and have profound effects on disease dynamics. Ultimately, a mechanistic understanding of how heterogeneity in transmission probabilities among exposure events contributes to disease dynamics remains an important outstanding question in the ecology and evolution of infectious diseases. Here we seek to elucidate how factors determining transmission success influence the probability of acquiring infection, epidemic dynamics, and pathogen evolution. Specifically, we will investigate how transmission determinants (pathogen dose, contact duration, and contact frequency) vary among exposure routes (direct and indirect) and ultimately contribute to the dynamics of an emerging multi-host disease of snakes. Snake fungal disease (SFD) is caused by, Ophidiomyces ophidiicola, which is an environmentally persistent fungal pathogen that, to date, has been documented in more than 42 species of wild snakes on three continents, and has contributed to the severe declines of several species. O. ophidiicola is transmitted through direct and indirect contacts, and the behavior of snake species affected by SFD naturally vary along an exposure duration and contact intensity gradient, making this an ideal system for understanding the effects of variation in exposure events on disease dynamics. This work will highlight important mechanisms that contribute to variation in snake declines, and more broadly, provide insight into the theoretical underpinnings and profound effects that factors determining successful transmission can have on infectious disease outbreaks. This proposal will leverage our recent advances in this multi-host system and use a combination of field, experimental, and modeling approaches to provide critical insight into how the dynamics of exposure events have cascading effects on infectious disease.