During routine histopathology of 180 juvenile hard clams, Mercenaria mercenaria, from a site in Virginia, USA, in 2007, we discovered a single individual heavily infected with a parasite resembling a haplosporidian, some members of which cause lethal bivalve diseases. Scanning electron microscopy of spores and sequencing of small subunit ribosomal DNA confirmed a new species: Minchinia mercenariae n. sp. Further sampling of clams at the site found prevalences up to 38% using polymerase chain reaction (PCR). No parasites were found in routine histological screening of the same individuals, but re-examination of clams judged positive by in situ hybridization (ISH) revealed very faintly staining plasmodia. No unusual mortalities have occurred among the sampled groups. Analysis of clams from Massachusetts to Florida by PCR failed to detect the parasite, but a haplosporidian found in a clam from New Jersey in 2001 was subsequently identified by ISH as M. mercenariae. No other haplosporidians have been reported in thousands of hard clams from the US east coast examined histologically since the mid-1980s. The discovery underscores critical questions about how to assess the risks associated with parasites in groups known to be lethal, but that themselves are not considered a problem.

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Perkinsus chesapeaki is reported from stout razor clams Tagelus plebeius in Delaware Bay, extending the known range of P. chesapeaki north of Chesapeake Bay. P. marinus, which causes dermo disease, is prevalent in cultured and wild oysters at this site, but was not detected in T. plebeius. Evidence for the presence of disseminated neoplasia, also reported from Chesapeake Bay, was equivocal. Although P. chesapeaki infections were associated with mortality events, light infection intensities and a general lack of histopathological evidence of disease limit inferences about a causal relationship. A comparison of Ray's fluid thioglycollate medium (RFTM)-based and PCR-based detection assays highlight differences in detection capabilities related to the quantity and type of tissue processed rather than assay sensitivity per se, a point that should be considered when surveying populations for disease prevalence. Investigators are further cautioned to use care when applying and interpreting diagnostic assays when used with novel species. KEY WORDS: Perkinsosis · Range extension · Tagelus plebeius · Perkinsus chesapeaki · Stout razor clam Resale or republication not permitted without written consent of the publisherDis Aquat Org 78: [243][244][245][246][247] 2008 Between August 2004 and November 2005, clams were collected opportunistically in response to reports of mortality and examined for evidence of potential pathogenic organisms (Table 1). The protocols and assays used varied among dates as described below. In fall 2006, a concerted effort was made to systematically collect a sample of live clams before and after a mortality event.To assess the magnitude of the November 2006 mortality event, 1 m 2 quadrats were haphazardly sampled along a 100 m transect to determine the density of dead clams at the surface. Dead clams were easily enumerated as the empty articulated valves from adult clams protruded 1 to several cm above the sediment surface. Then, to determine the density of live clams remaining in burrows beneath the surface, two 100 m 2 plots (each approximately 5 × 20 m) were sampled hydraulically along the mortality zone. Sediments were liquefied with a water pump and live clams collected when they rose to the surface. Based on the mortality transect, one plot was centered in a zone with a high density of dead clams and the other in a zone with a relatively low density of dead clams. No dead or moribund clams were recovered from below the surface. All live clams were measured (shell length and wet meat weight), shucked and examined for any gross abnormalities; evidence of parasites was assessed as described later.For Ray's fluid thioglycollate medium (RFTM) assays, clam tissues (mantle, gill or whole animal) were placed into culture tubes with RFTM and antibiotics, incubated in the dark, then processed using either tissue squash or body burden methods as described by Bushek et al. (1994). The Mackin Scale (Ray 1954, Mackin 1962) was used to rank infection intensities in tissue squashes from 0 (= no ...

The advent of molecular detection assays has provided a set of very sensitive tools for the detection of pathogens in marine organisms, but it has also raised problems of how to interpret positive signals that are not accompanied by visual confirmation. PCR-positive results have recently been reported for Haplosporidium nelsoni (MSX), a pathogen of the oyster Crassostrea virginica in 31 of 40 oysters from 6 sites in the Gulf of Mexico and the Caribbean Sea. Histological confirmation of the PCR results was not undertaken, and no haplosporidian has been reported from the numerous histological studies and surveys of oysters in the region. To further investigate the possibility that H. nelsoni is present in this region, we sampled 210 oysters from 40 sites around the Gulf of Mexico and Puerto Rico using PCR and 180 of these using tissue-section histology also. None of the oysters showed evidence of H. nelsoni by PCR or of any haplosporidian by histology. We cannot, therefore, confirm that H. nelsoni is present and widespread in the Gulf of Mexico and the Caribbean Sea. Our results do not prove that H. nelsoni is absent from the region, but taken together with results from previous histological surveys, they suggest that for the purposes of controlling oyster importation, the region should continue to be considered free of the parasite. KEY WORDS: PCR · Oyster · Crassostrea virginica · Molecular detection · Infection · Shellfish importation · Haplosporidian Resale or republication not permitted without written consent of the publisherDis Aquat Org 93: [251][252][253][254][255][256] 2011 C. virginica from Nova Scotia, Canada, to Biscayne Bay, Florida, USA (Haskin & Andrews 1988, Barber et al. 1997, Stephenson et al. 2003, but none of the several histological studies of oysters in the Gulf of Mexico have reported H. nelsoni or any other haplosporidian (Couch 1985, Gauthier et al. 1990, Fisher et al. 1996, Kim et al. 1998, Winstead et al. 2004, Kim & Powell 2006. The most comprehensive of these is the annual status and trends (S&T) MATERIALS AND METHODSCrassostrea virginica were collected between December 2007 and February 2008 at 32 sites representing 14 bay systems from lower Laguna Madre, Texas, to Florida Bay, Florida, USA, and C. rhizophorae were collected from 2 bays in Puerto Rico (Fig. 1, Table 1). In May and July 2010, C. virginica were sampled from 6 additional sites, representing 2 bay systems in Texas and 1 in Florida (Fig. 1, Table 1). All samples were express shipped directly to HSRL. Upon receipt, 12 oysters from each sample were opened using a shucking knife, which was rinsed in 10% bleach between each oyster. A section of gill about 4 mm wide and encompassing all 4 demibranchs approximately 6 to 7 mm posterior to the gill-palp junction was excised and preserved in 70% ethanol (EtOH) for PCR analysis. Dissecting instruments were scraped clean in a bleach-sand mixture, dipped in EtOH and flamed between each oyster. Between the PCR section and the palps, and adjacent to the piece of gill ta...