Virginia Institute of Marine Science
Proceedings of the National Shellfisheries Association
A localized epizootic caused by Dermocystidium marinum was induced in oysters in the York River, Virginia, to simulate natural epizootics in timing of infections and mortalities. Relative isolation was achieved by use of trays located on barren bottom. Decimation by Minchinia nelsoni (MSX) since 1960 has insured low populations of oysters and a relative scarcity of Dermocystidium. Trays spaced 15 feet apart exhibited epizootics which were progressively earlier and more vigorous in proportion to the number of infected oysters added (foci of infection). Minchinia infections were severe and at least 50 percent of the oysters died from this parasite. Dermocystidium spreads more rapidly and kills more quickly but requires dense populations and high temperatures. MSX is not localized and is much less affected by these limiting factors. In lower York River, new imports of disease-free oysters require one to three years to acquire Dermocystidium cases which initiate epizootics. During this period MSX decimates oyster populations, thereby preventing Dermocystidium from becoming epizootic.
Andrews, Jay D., Interaction of two diseases of oysters in natural waters (1967). Proceedings of the National Shellfisheries Association, 57, 38-49.