Abstract
Generalist microorganisms are the agents of many emerging infectious diseases (EIDs), but their natural life cyclesare difficult to predict due to the multiplicity of potential hosts and environmental reservoirs. Among 250 knownhuman EIDs, many have been traced to tropical rain forests and specifically freshwater aquatic systems, which act asan interface between microbe-rich sediments or substrates and terrestrial habitats. Along with the rapid urbanizationof developing countries, population encroachment, deforestation, and land-use modifications are expected toincrease the risk of EID outbreaks. We show that the freshwater food-web collapse driven by land-use change has anonlinear effect on the abundance of preferential hosts of a generalist bacterial pathogen, Mycobacterium ulcerans.This leads to an increase of the pathogen within systems at certain levels of environmental disturbance. Thecomplex link between aquatic, terrestrial, and EID processes highlights the potential importance of species communitycomposition and structure and species life history traits in disease risk estimation and mapping. Mechanismssuch as the one shown here are also central in predicting how human-induced environmental change, for example,deforestation and changes in land use, may drive emergence.