Over a 1-year period, bi-monthly estuarine surface water and plankton samples (63-200 and > 200 μm fractions) were assayed by polymerase chain reaction for the prevalence of total Vibrio parahaemolyticus, V. vulnificus and V. cholerae and select genes associated with clinical strains found in each species. Neither temperature nor plankton abundance was a significant correlate of total V. parahaemolyticus; however, the prevalence of genes commonly associated with clinical strains (trh, tdh, ORF8) increased with temperature and copepod abundance (P < 0.05). The prevalence of total V. vulnificus and the siderophore-related viuB gene also increased with temperature and copepod and decapod abundance (P < 0.001). Temperature and copepod abundance also covaried with the prevalence of V. cholerae (P < 0.05), but there was no significant relationship with ctxA or other genes commonly found in clinical strains. Results show that genes commonly associated with clinical Vibrio strains were more frequently detected in association with chitinous plankton. We conclude that V. parahaemolyticus, V. vulnificus, V. cholerae and subpopulations that harbour genes common to clinical strains respond distinctly to seasonal changes in temperature as well as shifts in the taxonomic composition of discrete plankton fractions.

Human norovirus (NoV) is the leading cause of nonbacterial gastroenteritis worldwide (3). The Centers for Disease Control and Prevention (CDC) estimate that 23 million cases of acute gastroenteritis due to NoV occur each year, with symptoms including acute-onset vomiting, watery nonbloody diarrhea with abdominal cramps, and nausea (35). NoV outbreaks are pervasive for many reasons, but particularly because the virus is highly contagious and environmentally hardy (7). Additionally, infected individuals can excrete millions of viral particles in feces, leading to large numbers in sewage (16). Without proper removal or inactivation during wastewater treatment, the viruses can be released into recreational and shellfishharvesting water bodies. Complete inactivation of NoV during sewage treatment is rare, and even in areas with proper wastewater treatment, contamination of oyster beds has been reported (5,16,17,32,38). Because bivalve molluscan shellfish are believed to act as filters for viruses and other microbes and because NoV is extremely infectious (as little as one viral particle is required for disease), the disease risk for consumption of raw oysters is high (27,33,40).Human NoV genogroup I (GI) and GII have been detected in oyster samples harvested from bays and estuaries worldwide (5,10,20). Ueki et al. (42) detected NoV in both shellfish and the surrounding river water in Japan and concluded that NoV contamination was most likely due to sewage and treated wastewater input into the river; however, no study has yet been able to characterize how NoV may be naturally distributed in an estuarine system, including in water, adhered to particles (including plankton), and in shellfish. The limitations are due in part to a lack of adequate detection methods specifically adapted to different environmental-sample types (8). Using a newly developed detection and quantification protocol (21), this study aimed to examine the distribution of NoV genogroups across a range of sample types within an estuarine system with the goal of better characterizing possible circulation of viruses between water, plankton, and oysters. MATERIALS AND METHODS Controls. (i) NoV-positive controls.Three NoV-positive fecal samples, representing genotypes GI.4, GI.3b, and GII.4 Minerva, were provided as controls for this study by the CDC. Stool samples were diluted to obtain a 20% suspension in phosphate-buffered saline (PBS), vortexed, and centrifuged at 15,700 ϫ g for 2 min.(ii) Viral-RNA extraction from stool. For stool samples, viral RNA was extracted from the clarified PBS extracts using the MagMAX-96 Viral Isolation Kit (Ambion, Austin, TX) and the KingFisher Instrument (Thermo Electron Corporation, Waltham, MA), which automatically purifies viral RNA. The purified RNA was eluted into 55 l elution buffer, provided in the kit.(iii) RNA transcript standards. To enable quantification by real-time reverse transcription (RT)-PCR, we used GI and GII plasmids (1) to generate RNA runoff transcripts. Briefly, the norovirus 3-kb plasmids were pu...

[1] Observations using a vessel-based acoustic Doppler current profiler conducted in two tidal channels with significant curvatures have shown persistent residual eddies. The residual eddies are clearly related to the bend of the channel. For a channel bending toward the north, the residual eddy on the east side of the channel tends to be clockwise, and the residual eddy on the west side of the channel tends to be counterclockwise. Water in these tidal channels is mostly well mixed or weakly stratified. Motivated by these observations, an analytic model is developed to study tidally induced mean circulation in a curved channel with arbitrary depth variations. A sinusoidal channel is used to simulate the effect of curved channels. A series of experiments with different parameters have shown consistently that a pair of residual eddies around the curvature exists. By analyzing the model results, it is found that advection is a major contributor to the residual eddies. Although the pressure gradient and the nonlinear wave propagation may not be negligible, especially for long channels, it is the advection that generates the vorticity of the residual eddies. The conclusion is true for both short and long channels. Here the division between a short and long channel is 0.6 of a quarter of the tidal wavelength. In addition, we also analyzed results from a finite volume numerical model for Lake Pontchartrain, which has curved tidal channels. The results demonstrate similar residual eddies as shown by the analytical model and the observations.