Parasites with free-living life stages often function as prey to generalist consumers. Their ubiquity throughout the water column suggests that parasite consumption is a major pathway for disease transmission in nearshore marine systems, particularly for sessile hosts that rely on suspension and deposit feeding activities to contact food particles. Competition for suspended particles, and its impact on per capita consumption, is well documented. Only recently however has competition for water-borne parasites been considered in studies of disease transmission. To illustrate this central connection between competition and disease transmission, we present results from mesocosm experiments varying the density of oysters and the dose of the etiological agent of Dermo disease, Perkinsus marinus. We found that the incidence of Dermo climbed with increasing per capita dose of Perkinsus marinus, but due to increased competition for suspended particles, fell with oyster density. The net result of such a competitive interaction via pathogen consumption is to inhibit the spread of disease, a phenomenon we describe as overfiltration. Overfiltration is challenging to predict in nature, but this concept delivers a new perspective for evaluating the observed persistence of Dermo disease in mid-Atlantic estuaries following the decline of oysters due to MSX. Can dense oyster populations overfilter Perkinsus marinus and minimize the impact of disease? The answer to this question will have important consequences for the management of oyster fisheries and oyster restoration anywhere Dermo is present.