Shared resources and disease dynamics in spatially structured populations

Infectious agents are likely to spread among animals that live together, yet we know remarkably little about how infectious agents move among social units. Sharing of resources - such as shared waterholes during a dry season - may provide an efficient route for the transmission of infectious agents among different social groups, and thus could represent an overlooked factor in understanding disease risks in spatially structured populations. We developed a spatially explicit individual-based model to investigate a situation in which multiple individuals of a single species converge at shared resources during periods of resource scarcity (i.e., “lean seasons”). We simulated the transmission of a fecally transmitted infectious agent in a spatially explicit meta-population of 81 social groups distributed on a square lattice. Time steps in the simulation corresponded to “days,” and we simulated disease dynamics over 10 yearly cycles of normal and lean seasons. The duration of the lean season varied across 1000 independent simulation runs, as did 12 other parameters sampled from a Latin hypercube distribution. Seasonal sharing of resources had marked effects on disease dynamics, with increasing prevalence of the infectious agent as lean season duration increased (and thus, duration of resource sharing also increased). Infection patterns exhibited three phases: an initial intermediate prevalence on the normal season home range, a rapid increase in prevalence around the shared resource during the lean season, and then a rapid decline in prevalence upon returning to the normal season range. These findings suggest that seasonal migration increases disease risk when animals congregate around resources, but enables them to escape soil-borne infectious agents upon returning to their original home ranges. Thus, seasonal sharing of resources has both negative and positive effects on disease risk.