Document Type



Virginia Institute of Marine Science

Publication Date



Marine Resource Report 2003-02


Samples collected monthly from the upper James River sites from January through May showed a decline in P. marinus prevalence during the 4 winter and spring following a typical annual pattern; however, annual minimums were atypically high, particularly at Point of Shoals and Wreck Shoal (12-44%). Unusually high salinity conditions and warm winter temperatures promoted high overwintering survival of the pathogen and an early onset of the disease in the summer months. Perkinsus marinus prevalence increased to 100% at all four of the upper river stations and record high infection intensities were observed at Deepwater Shoal and Horsehead Rock. It is likely that the high P. marinus infection intensities caused extensive oyster mortalities in the upper James River. Unusually high prevalences and intensities of H. nelsoni were also observed in the upper James River in 2002. The parasite was found at Horsehead Rock and Wreck Shoal in all months that samples were collected (January-May, July and October) and for the first time the parasite was found at Deepwater Shoal. Prevalences at Horsehead Rock ranged from 20% to 72%. The peak prevalence was observed in April; 48% of the oysters in that sample had moderate to heavy infections and it is likely that the parasite caused mortalities at this time. Down river at Wreck Shoal prevalence ranged from 4 to 52%, heavy intensity infections were found on most sample dates and the parasite probably caused mortality in this area too. Deepwater Shoal oysters were examined for H. nelsoni in October only. At that time prevalence was 28%, but all infections were light intensity



American Oyster Diseaeses, Virginia, Chesapeake Bay