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Abstracts
Session: The State of Oyster Disease
Current state of knowledge on dermo disease caused by Perkinsus marinus
Presented By:
Jerome F. La Peyre, Cooperative Aquatic Animal Health Research Program , Department of Veterinary Science, Louisiana State University jlapeyre@agctr.lsu.edu
Dermo disease continues to cause extensive oyster mortalities along the Gulf of Mexico and Western mid-Atlantic coasts. Over the last decade, research on dermo has produced important information about the parasite and its interaction with eastern oysters. In particular, this research has provided evidence to further support some of the existing approaches used to control dermo, but has also revealed potential new strategies to control dermo more effectively. Diagnostic assays for P. marinus (including the FTM body burden assay considered the gold standard for P. marinus diagnostic) have been improved and new rapid, quantitative and specific assays for P. marinus have been developed. These diagnostic assays have lead to studies confirming P. marinus transmission dynamics models and revealed valuable information on environmental and host factors affecting the course of P. marinus infection in eastern oysters. We still lack knowledge of factors controlling parasite growth in oyster tissues during progression of infection and factors controlling parasite elimination during regression of infection. This knowledge will be key to understanding the underlying process in disease dynamics and for controlling the disease through more rational approaches. In vitro culture systems for P. marinus have been useful in ascertaining the effects of environmental factors (e.g., salinity, temperature, pH, O2 and CO2) on the parasite viability and growth, in characterizing its lipid metabolism, in identifying potential virulence factors such as proteases and in determining the population genetic structure of the parasite. Cultured parasites however have been shown to be less virulent than wild-type parasites hindering studies to fully understand the disease process. Determining the reasons for the loss of virulence of cultured parasites and restoring their virulence should be a research priority. P. marinus virulence factors can then be identified more easily and targeted to control dermo. Commercial inhibitors of P. marinus proteases for example have been shown to inhibit the growth of P. marinus in axenic culture and to decrease the number of parasites in infected hemocytes in vitro. Inhibitors of P. marinus proteases have also been recently purified from eastern oyster plasma along with other types of defense factors that are deleterious to P. marinus. The role these host defense factors play in increased dermo resistance recently observed in certain oyster stocks will need to be ascertained. Recently acquired information about P. marinus biology suggests promising new approaches to limit dermo mortalities, but also confirms the usefulness of a selective breeding program as a slow but proven method to increase dermo resistance in eastern oysters.
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