Perkinsus marinus tissue distribution and seasonal variation in oysters Crassostrea virginica from Florida, Virginia and New York

Abstract

Apalachicola Bay (FL), Chesapeake Bay (VA), and Oyster Bay (NY). Gill, mantle, digestive gland, adductor muscle, hernolymph, and remaining tissue (including gonadal material and rectum) were dissected from 20 oysters from each site at each collection time. Samples were separately diagnosed for P. marinus infections by incubation in Ray's Fluid Thioglycollate Medium (RFTM) and subsequent microscopic quantification of punfied enlarged hypnospores. At all sampling times and sites, average P. marinus infection intensity (g wet wt tissue-' or m1 hemolymph-') was lowest in hemolyrnph samples, and generally highest in the digestive gland. Perkinsus marinus prevalence was 100% at both FL and NY sites for each of the 5 collection times, and, for the VA site, was less than 100% in only 1 month (May 1994). Seasonal intensity patterns and mean total body burdens differed among the sites. Average body burden was highest in VA during October and progressively declined to a minimum in May. This decline was probably due to mortality of heavily infected oysters and diminution of parasite activity associated with colder temperatures and reduced salinities. Intensities varied little during the months of October and December at both the FL and NY sites. Minimum average intensities were observed in March in FL oysters and May in NY oysters. Relatively high P. rnarinus infection levels that persisted throughout the winter in NY oysters compared with VA oysters could reflect constant high salinity in Long Island Sound which favors parasite activity, and also rapid decline in temperature in the fall that may have prevented epizootic oyster rnortalities.

Defining Optimal Freshwater Flow for Oyster Production: Effects of Freshet Rate and Magnitude of Change and Duration on Eastern Oysters and Perkinsus marinus Infection

“…While low salinity and reduced osmolalities clearly are associated with reduced infection intensities, temperature is also held to be a dominant control on disease progression or reduction and must be considered in explaining disease dynamics Soniat 1996;Soniat and Kortright 1998). While low temperatures have been suggested to be critical in reducing infection intensities in colder waters (i.e., Oliver et al 1998;Ford and Smolowitz 2007), it is unlikely to have played a major role at our sites, which all experienced the same temperature regime with water temperatures never falling below 6°C. Exposure of P. marinus to low temperatures (<4°C) for 30 days in vitro was recently found to have minimal effect on viability (La Peyre et al 2008).…”

Perkinsosis in molluscs: A review

“…Due to the differential distribution of Perkinsus spp. in molluscan tissues, as assessed by selective incubation of the host organs in RFTM (Choi et al 1989;McLaughlin and Faisal 1999;Oliver et al 1998), the technique has been modified for P. marinus in oyster (Fisher and Oliver 1996) and for P. olseni/P. atlanticus in carpet shell clam (Almeida et al 1999) to include the whole bivalve body in the assay.…”

Comparison of in vitro-cultured and wild-type Perkinsus marinus. II. Dosing methods and host response

“…Likely routes of entry were documented by Dungan et al (1996) by using a fluorescentlabeled anti-P. marinus antibody: 21 d after experimental challenge, they found P. marinus in the epithelium and connective tissues of the mantle, palps, and gill, and in the connective tissues around the gut, but not in the epithelium of this organ. It is relevant that all the reports showing the digestive gland to have the highest P. marinus densities come from studies of wild oysters in which infections were well-established rather than newly acquired (Choi et al 1989, Mackin 1951, Oliver et al 1998. As postulated by Dungan et al (1996), P. marinus may become concentrated in the digestive gland and, for some reason, this may increase the parasite's fitness.…”