Infection and Mortality Infectious stages are present in the warm months from May through October. Initial infections are usually detected in June. Dermo can be characterized as a slow killing disease. It may take up to three years after initial infection to cause death in an oyster although death in the second summer is typical. Mortalities occur from July through November.
Oysters die due to tissue lysis and occlusion of hemolymph vessels.
Prevalence and intensity of the disease decreases during the winter months. Some parasites remain dormant and will proliferate as temperatures rise in the spring, releasing stages that initiate another round of infection. History Dermo disease caused extensive oyster mortalities in the Gulf of Mexico in the late 1940s. Later, it caused chronic and occasionally massive mortalities in the Chesapeake Bay. Since 1990, Dermo has been detected in Delaware Bay, Long Island Sound, Massachusetts, Rhode Island and Maine.