Print PageGlobal changes in the biogeochemical cycles of phosphorus (P) and especially nitrogen (N) have been linked to alterations in primary production, decomposition, community structure, and water quality. Less clear, however, is how changing nutrient concentrations affect host-pathogen interactions and the risk of infectious diseases in humans, plants, domestic animals and wildlife. Because many parasites have multiple hosts, including the majority of those involved with emerging infections, the effects of N and P on transmission are often indirect and may be difficult to predict a priori, challenging efforts to forecast under what conditions increases in infection or pathology might be expected.
Results/Conclusions
While numerous correlational studies have suggested a link between changing nutrient cycles and disease risk, a more recent body of experimental studies have begun to provide mechanistic insights into this relationship, with examples ranging from mosquito-borne infections of humans, fungal pathogens of plants, bacterial infections of fishes and infectious diseases of corals. Drawing upon this body of work as well as our own cross-sectional surveys and experimental studies involving amphibian diseases, we identify patterns and explore the mechanisms through which N and P are likely to alter infection risk. Available evidence suggests that nutrient enrichment causes both increases and decreases in parasitism, but is most likely to favor opportunistic or generalist pathogens with low dependency on host density, parasites with intermediate hosts or vectors that respond strongly to nutrients, or infections that exacerbate pathology in hosts already stressed by other effects of nutrients (e.g., hypoxia). Although many uncertainties persist, we argue that this linkage warrants increased research attention in light of forecasted increases in nutrient concentrations in tropical regions that already support a high diversity of human and wildlife pathogens.
