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A Study on the Protozoan Pathogens Perkinsus marinus and Haplosporidium nelsoni in the Easter Oyster, Crassostrea virginica within Georgia’s Recreational Shellfish Harvest Areas


PIs: Ellie Covington and Alan Power (Univ of Georgia Marine Extension Service)

Support: University of Georgia Marine Extension Service

Timeframe: Jan 2006 - ongoing (quarterly)

Project Overview:
      Since the 1960’s scientists have documented mass oyster mortalities occurring along the eastern seaboard of the US due to waterborne protozoan parasitic infections.  Two parasites of particular concern are Perkinsus marinus, and Haplosporidium nelsoni.  Both parasites tend to flourish in salinities above 15 and new infections generally occur during warmer months.  P. marinus attacks the digestive system and may inhibit reproduction, and growth before causing death.  Oysters have shown resistance and may survive with a light infection for a year or more.  H. nelsoni first attacks the gill tissue, and then spreads to digestive tissue and to the rest of the body.  Transmission methods for H. nelsoni remain unknown.
      These parasites are harmless to humans who consume infected oysters but could lead to a serious decline in Georgia’s oyster resources.  There is no known method for eradicating these parasites in the natural environment.  While the diseases have been examined at certain locations over defined periods of time, there has not yet been a coast wide spatial and temporal analysis of disease dynamics in the state.  We have therefore initiated a long term quarterly monitoring program focusing on Perkinsus marinus and Haplosporidium nelsoni prevalence and intensity at public recreational harvest areas in Chatham, Liberty, McIntosh, Glynn and Camden counties.

Results to date :
The recent results show an increase in the number of infected oysters and an increase in the degree of infection between winter and summer months. 

         Our study employs the Perkinsus marinus assay protocol as described by Powell and Ellis (1998).  This method involves a 14-day incubation period of tissue stored in Ray’s Fluid Thioglycollate Medium (RFTM).  After the incubation period the tissue is examined microscopically and assigned an infection intensity rating based on the semiquantitative scale of infection adapted from Mackin (1962) by Craig et al. (1989).  This has been the traditional method of Perkinsus marinus detection.  It is relatively inexpensive but is labor intensive and subject to user bias when reading slides and my result in false negatives when looking at tissues with very low infection levels.  We are therefore investigating a new technique that has been developed for assessing Perkinsus marinus using PCR methodology (Gauthier et al., 2006).  While this method is certainly quicker and perhaps more accurate it has the drawback of being much more expensive.  We would welcome the opportunity to work with others and to pursue funding to support a long term shellfish disease monitoring program.

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This page was updated October 13, 2006