Science Serving Maryland's Coasts


Assessing the presence and virulence of "Dermo" disease in the environment using a PCR-based diagnostic assay for the extrachromosomal plastid genome of Perkinsus marinus .

Principal Investigator: 

Gerardo R. Vasta

Start/End Year: 

1995 to 1997


Center of Marine Biotechnology, University of Maryland Biotechnology Institute

Co-Principal investigator: 

Adam G. Marsh, Center of Marine Biotechnology, University of Maryland Biotechnology Institute



We plan to apply the methodologies developed from our current NMFS-funded project for mtDNA markers, DNA fingerprinting, RNA probes and PCR technologies to quantify low-levels of Perkinsus marinus infections in order to fully describe the etiology of this oyster disease. Our progress in working with genetic markers of P. marinus has: Developed a sensitive PCR-based diagnostic assay for detecting P. marinus infections ; Identified an extrachromosomal relic plastid-genome in P. marinus that is indicative of this species' close affinity to dinoflagellates and a photosynthetic ancestor; Described two ribosomal RNA genes that have been used in a phylogenetic reconstruction of the ancestral lineages of P. marinus ; Quantified tissue-specific P. marinus infection levels in field populations of oysters collected from Maine, Chesapeake Bay and Louisiana; and Assessed the population genetics of P. marinus along the Atlantic coast and Gulf of Mexico. Given the success of our work within the first year of funding, we are confident that we will be able to extend this work into a series of genetic diagnostic tests for: a) cryptic infections in hatchery stocks; b) infection mechanisms of oyster juveniles and spat; c) routine certification of disease-free oyster spat and juveniles from hatcheries; d) putative P. marinus secondary vectors and intermediate hosts; and e) detecting P. marinus in environmental water samples. Focus the application of our quantitative molecular (PCR) diagnostic techniques for practical field purposes regarding the etiology of this oyster disease. With this information we will be able to identify additional geographic P. marinus races or types, that will improve the management strategies for each particular region depending on the prevalent parasite type. We will focus on the genetic structure of P. marinus populations in Chesapeake Bay in order to assess the relative prevalence and virulence of P. marinus types (Type I or lI). We will evaluate the onset of P. marinus infections in oyster larvae and spat for routine certification of disease-free oyster from hatcheries, and in disease resistant stocks in Delaware Bay, as a collaborative effort with Dr. S. Allen, which will contribute to determine if these selected oysters exhibit increased resistance for P. marinus types. This will be compared to unselected stocks, including those currently used for restoration of affected areas (Severn River), and present in natural reefs (James and Rhodes Rivers) in the Chesapeake Bay. In the aforementioned sites we will evaluate the presence of the parasite in the associated invertebrate and vertebrate fauna that may constitute alternative hosts or reservoirs. Novel technologies using DNA probes for the quantitation of P. marinus life stages in environmental waters will be developed.