Vector-borne zoonotic disease agents, which are knownto often infect multiple species in the wild, have been identified asan emerging threat to human health.Understanding the ecology ofthese pathogens is especially timely, given the continued anthropo-genic impacts on biodiversity. Here, we integrate empirical scalinglaws from community ecology within a theoretical reservoir-vector-pathogen framework to study the transmission consequences of hostcommunity structure and diversity within large assemblages. Weshow that heterogeneity in susceptibility of the reservoir species pro-motes transmission “dilution,” while a greater vector species richness“amplifies” it. These contrasting transmission impacts of vector andreservoir communities can yield very differentepidemiological pat-terns. We demonstrate that vector and reservoir species richness canexplain per se most of the pathogen transmission observed for WestNile virus in different parts of the United States, giving empiricalsupport for the validity of these opposing theoretically predictedeffects. We conclude that, in the context of disease emergence, theintegration of a community perspective can provide critical insightsinto the understanding of pathogen transmission in wildlife.