Developing a population with high prevalence capable of sustaining an epizootic from a population of lower prevalence requires that some portion of the population retain the infection and be able to locally proliferate abundant infective particles. The general question of how epizootics are initiated and terminated in marine invertebrate populations and how this process is supported by transmission is addressed through a theoretical framework for disease transmission that represents a population of susceptible and infected individuals (SI model). Disease transmission is through infectious particles in the environment rather than by contact or a disease vector. Susceptible individuals acquire infections by filtration and a dose-response relationship is used to determine the development of infection. Model parameterizations are based on experimental studies of dermo disease in Eastern oysters (Crassostrea virginica). The initial application of the time-dependent model focused on determining the relationship between infective dose, infectious particle flux, and population density. Simulations show that transmission of infectious particles maintains disease prevalence in Eastern oyster populations at a steady and relatively high level, which balances losses by mortality and recruitment of new individuals.

Eileen Hofmann received a Ph.D. in Marine Sciences and Engineering from North Carolina State University. Her research interests are in the areas of physical and biological interactions in marine ecosystems and descriptive physical oceanography. She is part of a research group that has been working on the ecology of marine diseases that affect bivalves.

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