Showing papers on "Oyster published in 1995"

An outbreak of Norwalk virus gastroenteritis associated with eating raw oysters. Implications for maintaining safe oyster beds.

Abstract: Objective. —To determine the characteristics and the cause of an outbreak of gastroenteritis associated with eating raw oysters. Design. —Survey of groups of persons reporting illness to the health department after eating oysters; survey of convenience sample of oyster harvesters; and tracing of implicated oysters. Setting. —General community. Main Outcome Measures. —Relative risk for illness after oyster consumption, source bed of contaminated oysters, presence of antibodies to Norwalk virus in serum, presence of a Norwalk virus in stool by direct electron microscopy and reverse transcription—polymerase chain reaction (RT-PCR), and DNA sequences of RT-PCR products. Results. —Seventy (83%) of 84 persons who ate raw oysters became ill vs three (7%) of 43 people who did not eat raw oysters (relative risk, 11.9; 95% confidence interval, 4.0 to 34.2). Eleven (79%) of 14 serum pairs had at least a fourfold increase in antibody to Norwalk virus. All 12 stool samples tested were positive by electron microscopy and/or RT-PCR for Norwalk virus. The RT-PCR products from all seven stool samples tested had identical DNA sequences. Implicated oysters were harvested November 9 through 13, 1993, from a remote oyster bed. Crews from 22 (85%) of 26 oyster harvesting boats working in this area reported routine overboard disposal of sewage. One harvester with a high level of antibodies to Norwalk virus reported having gastroenteritis November 7 through 10 and overboard disposal of feces into the oyster bed. Conclusions. —This outbreak was caused by contamination of oysters in the oyster bed, probably by stool from one or more ill harvesters. Education of oyster harvesters and enforcement of regulations governing waste disposal by oyster harvesting boats might prevent similar outbreaks. (JAMA. 1995;273:466-471)

A multistate outbreak of oyster-associated gastroenteritis: implications for interstate tracing of contaminated shellfish

Abstract: In November 1993, clusters of gastroenteritis in six states following oyster consumption were investigated to identify common features, and stool samples were obtained to identify a pathogen. Efforts were made to account for all potentially contaminated oysters using harvest tags and the interstate recall system. Consumption of oysters was associated with illness in 10 clusters; no other food was implicated. A Norwalk-like virus was detected by electron microscopy in 9 of 18 samples and by reverse transcription-polymerase chain reaction in 20 of 26 samples from 6 clusters. Nucleotide sequences of a 123-bp fragment from all specimens were identical, consistent with a common source outbreak. Implicated oysters were harvested from the Louisiana coast between 9 and 12 November. Although some were recalled and destroyed, most oysters harvested from the area during this time remain unaccounted for. Current regulations and commercial practices need to be revised to permit thorough tracing and recall of contaminated oysters and to improve control of future epidemics.

Experimental and Histological Studies of Four Life-History Stages of the Eastern Oyster, Crassostrea virginica, Exposed to a Cultured Strain of the Dinoflagellate Prorocentrum minimum.

Abstract: Effects of the dinoflagellate Prorocentrum minimum (strain EXUV) upon four life-history stages of the eastern oyster--embryos, feeding larvae, newly set spat, and juveniles--were investigated in laboratory exposure studies. Embryonic development was not affected significantly by living, heat-killed, or sonicated cells, or by growth-medium extracts from P. minimum cultures. Feeding larvae, however, showed poor growth and poor development of the digestive system when fed P. minimum, as compared with larvae fed Isochrysis sp. (strain T-ISO). Growth of larvae fed mixed P. minimum + Isochrysis diets was intermediate. Larvae and newly set spat that had been fed a diet of 1/3 P. minimum + 2/3 Isochrysis exhibited distinctive changes in digestive-system anatomy. Spat showed an abnormal accumulation of lipid in the stomach epithelium. Absorptive cells in the digestive glands of both larvae and spat contained accumulation bodies, often with a laminated, fibrous appearance in preparations for transmission electron microscopy. These accumulation bodies were PAS (periodic acid-Schiff) positive and may correspond to autolysosomal bodies within P. minimum cells. Juvenile oysters developed the ability to digest P. minimum, but only after a refractory period of about 2 weeks, during which most P. minimum was filtered but rejected as pseudofeces. The linking of accumulation bodies within absorptive cells of oyster digestive diverticula with dinoflagellate autolysosomal bodies suggests a mechanism by which some dinoflagellates interfere with feeding in phytoplankton grazers.

Suppression of chemiluminescence of eastern oyster (Crassostrea virginica) hemocytes by the protozoan parasite Perkinsus marinus

Abstract: Experiments were conducted to determine the ability of the protistan parasite, Perkinsus marinus, to inhibit chemiluminescence of hemocytes from the eastern oyster, Crassostrea virginica. Luminol-enhanced chemiluminescence (CL) was used to measure the production of reactive oxygen intermediates (ROI) generated by oyster hemocytes using zymosan as a stimulant. To determine whether P. marinus suppresses ROI evoked from zymosan-stimulated hemocytes, live or heat killed P. marinus in filtered estuarine water (YRW) (salinity = 20 ppt) were added to (1) zymosan-stimulated hemocytes after CL reached its peak, or (2) hemocytes at the same time as zymosan, and reduction of CL responses were recorded. In both tests, controls received only estuarine water. Live P. marinus meronts significantly suppressed ROI production by zymosan-stimulated hemocytes. The suppression of ROI production was dose dependent. Suppression of ROI production from zymosan-stimulated hemocytes by heat killed P. marinus was significantly less than by live P. marinus. Similarly, CL of hemocytes was reduced, though not significantly when hemocytes were exposed to YRW preincubated with P. marinus. When P. marinus meronts were used as a stimulant, no CL response was elicited. Results of this study suggest that P. marinus cells are able to suppress ROI release from oyster hemocytes, thus evading this component of the host's defense.

Effect of oyster mariculture on submerged aquatic vegetation: an experimental test in a Pacific Northwest estuary

Abstract: The effects of commercial culture of oysters Crassostrea gigas, on submerged aquatic vegetation (SAV), Zostera manna, were examined w ~ t h rephcated field expenments in the South Slough estuary Oregon USA Both stake and rack methods of oyster culture resulted In signlf~cant decreases in the abundance of SAV compared to undisturbed reference areas SAV cover in both stake and rack treatments was less than 25% of that In reference plots after 1 yr of culture, and was absent from rack treatments after 17 mo of culture Field experments using marked plants revealed no difference in growth between plants in stake and reference plots Compansons of sediment surface topography demonstrated that oyster culture resulted in significantly greater sediment deposition in stake plots and greater eroslon In rack plots Silt-clay fractions and carbon content of sediments tended to increase w ~ t h stake culture and decrease w ~ t h rack culture but only for carbon content at racks were the differences significant between culture and reference plots Stake culture likely affected SAV via increased sedimentation and direct physical disturbance dunng placement and harvest, while increased eroslon and perhaps shading resulted in the marked decrease in SAV co~ncident with rack culture These results indicate the potential for significant loss of SAV from estuanne ecosystems where these methods of oyster culture and SAV coincide

Early recruitment and growth of the American oyster Crassostrea virginica (Bivalvia: Ostreidae) with respect to tidal zonation and season

Abstract: Survival and growth of newly settled oysters were measured at suband mtertidal treatment levels during the first month of post-settlement life in the York River, Virginia, USA. Controlled settlement of hatchery-reared larvae m the laboratory and image analysis techniques allowed for individual oysters grown in the field to be tracked through time. High mortality occurred within 1 wk postsettlement at all tidal heights m 3 experiments which spanned the natural recruitment period. This imtial mortality strongly influenced later abundance, as weekly mortality rates decreased sharply after 2 wk. Additionally, all recruits were eliminated from the mid-intertidal zone and above (>25 % aerial exposure) during high temperature periods. Only in autumn did recruitment occur in the mtertidal area occupied by natural oyster populations. In contrast, low intertidal and subtidal populations persisted through the month long experiments where adult oysters were rare Growth (shell area) of intertidal oysters exposed >25 % was reduced relative to more immersed oysters. Density-dependent growth was not observed While the natural oyster population appeared to be relegated to the suboptimum mtertidal, successful recruitment to this zone was limited on a seasonal basis by lethal air temperatures >30°C The mortality agents which structure the mtertidal population affect recently settled and juvenile oysters

A semiquantitative PCR assay for assessing Perkinsus marinus infections in the eastern oyster, Crassostrea virginica

Abstract: A 3.2-kb fragment of Perkinsus marinus DNA was cloned and sequenced. A noncoding domain was identified and targeted for the development of a semiquantitative polymerase chain reaction (PCR) assay for the presence of P. marinus in eastern oyster tissues. The assay involves extracting total DNA from oyster hemolymph and using 1 microgram of that DNA as template in a stringent PCR amplification with oligonucleotide primers that are specific for the P. marinus 3.2-kb fragment. With this assay, we can detect 10 pg of total P. marinus DNA per 1 microgram of oyster hemocyte DNA with ethidium bromide (EtBr) staining of agarose gels, 100 fg total P. marinus DNA with Southern blot autoradiography, and 10 fg of total P. marinus DNA with dot-blot hybridizations. We have used the sensitivity of the PCR assay to develop a method for estimating the level of P. marinus DNA in oyster hemolymph and have successfully applied this technique to gill tissues. Our semiquantitative assay uses a dilution series to essentially titrate the point at which a P. marinus DNA target is no longer amplified in a sample. We refer to this technique as "dilution endpoint" PCR. Using hemocytes obtained by withdrawing a 1-ml sample of hemolymph, this assay provides a nondestructive methodology for rapidly screening large numbers of adult oysters for the presence and quantification of P. marinus infection levels. This technique is applicable to other tissues (gills) and could potentially be applied to DNA extracts of whole larvae or spat.

A Sensitive and Specific DNA Probe for the Oyster Pathogen Haplosporidium nelsoni

Abstract: Haplosporidium nelsoni is a pathogen of the eastern oyster, Crassostrea virginica, along the middle Atlantic coast of the U.S. Genomic DNA was extracted from H. nelsoni plasmodia and small subunit (SSU) rDNA was amplified by PCR, cloned and sequenced. The sequence of H. nelsoni SSU rDNA was aligned with that of another haplosporidian, Minchinia teredinis, and with SSU rDNA data of C. virginica and various protists in GenBank. A 21-base oligonucleotide unique to H. nelsoni, designated MSX1347, was commercially synthesized and tested for sensitivity and specificity. In dot blot hybridizations the probe detected 100 pg of cloned H. nelsoni rDNA and the presence of H. nelsoni in 1 microgram of genomic DNA from an infected oyster. It did not hybridize with 1 microgram of genomic DNA from uninfected C. virginica or with cloned SSU rDNA of M. teredinis. The probe was further tested for specificity with in situ hybridizations on AFA-fixed, paraffin-embedded tissue sections. The probe hybridized well with H. nelsoni plasmodia and immature spores, but poorly with mature spores. The probe did not hybridize with oyster tissue, with other common oyster parasites such as P. marinus or Nematopsis sp., or with the haplosporidians Haplosporidium louisiana from mud crabs (Panopeus spp.), Haplosporidium costale from C. virginica or M. teredinis from shipworms (Teredo spp.).

Selective particle ingestion by oyster larvae ( Crassostrea virginica ) feeding on natural seston and cultured algae

Abstract: I investigated selective particle ingestion by oyster larvae (Crassostrea virginica) feeding on natural seston from Chesapeake Bay and laboratory-cultured algae of different sizes or chemical content. In 15 of 16 experiments with complex natural suspensions as food, small( 150 μm) larvae selected most strongly for small (2 to 4 μm) food particles, but in the presence of a large (>10 μm)-cell dinoflagellate bloom, large larvae strongly selected much larger (22 to 30 μm) food material (presumably dinoflagellates). When fed simplified mixtures of four cultured algal species (Synechococcus bacillaris, Isochrysis sp., Dunaliella tertiolecta, and Prorocentrum minimum) ranging in size from 1 to 11 μm, small larvae preferred 1 μm algae while large larvae preferred 11 μm algae. In experiments with algal mixtures, and with suspensions of natural particles and added algae, large larvae preferred algal species harvested from exponential-phase cultures over other species from stationary-phase cultures. Larval ingestion rates of the cultured alga Thalassiosira pseudonana were about three times higher for cells with a low carbon:nitrogen ratio (7.2:1) than for high C:N ratio (16.2:1) cells when these cells were offered separately in suspensions of equal concentration. As a result, more algal cells, algal C, and algal N was ingested by larvae fed low C:N cells. However, larvae did not show a significant preference for either type of cell when they were offered in a 1:1 cell mixture. Feeding patterns of C. virginica larvae in natural food suspensions can vary with the composition of these complex suspensions, and ingestion seems dependent not only on the size, but on the growth rate and chemical quality of food particles.

In vitro interaction of Perkinsus marinus merozoites with eastern and pacific oyster hemocytes

Abstract: This study compared hemocyte responses of eastern and Pacific oysters to Perkinsus marinus, in vitro. Except for the percentage of hemocytes associated with P. marinus there was little or no significant difference between eastern and Pacific oysters with regard to their hemocytic response to P. marinus. In phagocytosis assays, merozoites were bound to all hemocyte types but in unequal proportions, unlike zymosan which was found predominantly associated with granulocytes. The number of merozoites enlarging in Ray's fluid thioglycollate medium after incubation with hemocytes in plasma for one day was significantly lower than after incubation in plasma alone in both oyster species. Electron microscopy or merozoites indicated that the parasites were rapidly phagocytosed and that some of the merozoites showed signs of degeneration in less than 12 h. The results suggest that limited intracellular killing of P. marinus had occurred, but was probably not mediated by oxygen metabolites, since no increase in chemiluminescence was observed when hemocytes of either eastern or Pacific oysters were exposed to merozoites.

Distribution of polycyclic aromatic hydrocarbons in oyster (Crassostrea virginica) and surface sediment from two estuaries in South Carolina

Abstract: The concentration of polycyclic aromatic hydrocarbons (PAHs) was determined in oysters and sediments collected from two high salinity estuaries from the coast of South Carolina. The two estuaries were Murrells Inlet (urban), an estuary receiving urbanized drainage and run-off, and North Inlet (non-urban), receiving drainage from heavily forested terrarin and minimal anthropogenic input. A minimum of thirty (30 stations were sampled in Murrells and North Inlets, respectively. A composite oyster sample (n=30) was analyzed for each station. For sediment, a sample from the top 3–5 cm of the sediment surface from each station was analyzed. In oyster from Murrells Inlet, total PAHs concentrations within the 75 percentile were located in the northern portion of the estuary near marinas, adjacent to residential areas of high population density, near commercial enterprises or run-off from storm drains. Total PAHs within the 25 percentile were located near the mouth of the estuary. These results showed a PAHs concentration gradient in the estuary that was highest in narrow creeks, where the urban shore interfaced with tidal creeks and lowest at the mouth of the estuary. In the case for sediment, a similar gradient was observed. In comparing the mean total PAHs of the two inlets, Murrells Inlet had significantly higher (p<0.01) total PAHs concentrations than North Inlet for oyster and sediment, respectively.

Effect of chill and freezing temperatures on survival of Vibrio parahaemolyticus inoculated in homogenates of oyster meat.

Abstract: Survival of Vibrio parahaemolyticus was determined in oyster meat homogenates at various temperatures. (4 degrees C, 0 degrees C, -18 degrees C and -24 degrees C) and bacterial levels (10(2), 10(4), 10(5) and 10(7) ml-1). In all cases, the numbers of V. parahaemolyticus were a logarithmic function of log time. This study indicates that high numbers of V. parahaemolyticus can be inactivated at low temperatures. The time of total inactivation depends on the initial number of micro-organisms and incubation temperature. It is possible to use this information to determine the storage time necessary to reduce V. parahaemolyticus hazards in fish.

Geographical patterns of variability at allozyme loci in the European oyster Ostrea edulis

Abstract: The variability of 14 enzyme-coding genes has been analysed in samples from 19 populations of the oyster Ostrea edulis L., collected along the Atlantic and Mediterranean coasts of Europe. We found an abundance of clines, which appeared at 8 loci, including the most polymorphic (AP-2 *, ARK *, EST-4 *, MDH-2 *, ME-1 *, 6PGH *, PGI * and PGM *). Another 6 loci (ALDH *, EST-3 *, EST-5 *, IDH-2 *, MDH-1 *, ME-2 *) exhibited V-shaped patterns of gene-frequency variation, with clines at one or both sides of the Straits of Gibraltar. The observation of coincident clines at many loci can be explained by a model of secondary intergradation. The geographical location of the midpoints of the clines and V-shaped patterns suggests the existence of two ancient Atlantic and Mediterranean oyster stocks which became differentiated in allopatry and subsequently merged. Clines observed along Atlantic and/or Mediterranean coasts at the loci with V-shaped patterns must have arisen independently. The large heterogeneity observed in the levels of gene differentiation (G ST ) across loci (G ST ranged from 0.008 to 0.290) and important differences in estimates of gene flow obtained by different methods suggest that the populations of O. edulis are not in genetic equilibrium. Lack of population equilibrium can be due to natural selection and/or restrictions to gene flow. The average among-population variability was higher than in other oyster species that do not show incubatory habits, and represented 8.8% of the total heterozygosity. Levels of intrapopulation variability were lowest in populations from the North Atlantic, suggesting low population sizes in that area.

Condition index and chemical composition of meats of Sydney rock oysters (Saccostrea commercialis) and Pacific oysters (Crassostrea gigas) at four sites in Port Stephens, NSW

Abstract: Adult Sydney rock oysters (Saccostrea commercialis) and Pacific oysters (Crassostrea gigas) were kept on commercial oyster leases at three intertidal sites in Port Stephens, New South Wales, and subtidally under an experimental raft at a fourth site between July 1988 and September 1989. Oysters were sampled from each site at approximately monthly intervals for chemical and histological analysis. Condition index and percentage glycogen of Pacific oysters were higher than those of Sydney rock oysters during winter and spring but tended to be lower during summer and autumn. Gonads of Pacific oysters matured two months earlier than those of Sydney rock oysters, with spawning being observed at all sites in October. Sydney rock oysters spawned later during December-January and did not lose as much condition after spawning as Pacific oysters. The absolute amount of glycogen in the meats of both species dropped at the expense of protein and lipid as the oysters became fully ripe. For both species, general condition of the oysters was best when they were grown subtidally under the raft, although both species were badly affected by invasion of the protistan parasite Mikrocytos roughleyi at this site. Poorest overall condition for both species occurred at a site (Karuah River) that experienced decreased salinities and increased turbidity after rain. Highest condition indices were found in Sydney rock oysters, at the site most dominated by coastal conditions (Corrie Island).