New diseases continue to appear in animal populations. This disturbing trend prompts challenging questions about disease, such as, why do some populations become infected and not others? Recently, ecologists have suspected that other species, such as those that provide food for hosts, compete with hosts for food, and prey on sick hosts, can inhibit or facilitate disease spread. Therefore, interactions with other species may influence the distribution of wildlife disease. However, an exploration of this possibility requires an integration of epidemiology with community ecology. Few disease systems offer opportunities for such integration, but Hall and Caceres aim to exploit an experimentally tractable one using an aquatic parasite (fungus)-host (water flea, Daphnia) system. They will harness decades of study of Daphnia as grazers of algae, as competitors with other zooplankton for that algae, and as prey for fishes and invertebrates. Each of these interactions likely influences disease spread among the Daphnia hosts. For instance, quantity and quality of food resources influence the production of infective forms of the parasite. However, because they consume but do not produce these infective forms, other planktonic competitors may reduce disease. Finally, predators may inhibit disease by eating infected hosts. These mechanisms are complex and will thus be addressed by constructing mathematical models, refining those models using experiments, and testing model predictions with observations of epidemics. The processes examined in this study and the modeling work should apply to many other disease systems. Ultimately, this work will produce theories that can guide efforts to understand and control disease in wildlife populations.
