Model results indicated that the mean WWTP influent concentration of NoV GII (3.9 log 10 gc/liter; 95% credible interval [CI], 3.5, 4.3 log 10 gc/liter) is larger than the value for NoV GI (1.5 log 10 gc/liter; 95% CI, 0.4, 2.4 log 10 gc/liter), with large variations occurring from one WWTP to another. For WWTPs with mechanical systems and chlorine disinfection, mean log 10 reductions were ؊2.4 log 10 gc/liter (95% CI, ؊3.9, ؊1.1 log 10 gc/liter) for NoV GI, ؊2.7 log 10 gc/liter (95% CI, ؊3.6, ؊1.9 log 10 gc/liter) for NoV GII, and ؊2.9 log 10 PFU per liter (95% CI, ؊3.4, ؊2.4 log 10 PFU per liter) for MSCs. Comparable values for WWTPs with lagoon systems and chlorine disinfection were ؊1.4 log 10 gc/liter (95% CI, ؊3.3, 0.5 log 10 gc/liter) for NoV GI, ؊1.7 log 10 gc/liter (95% CI, ؊3.1, ؊0.3 log 10 gc/liter) for NoV GII, and ؊3.6 log 10 PFU per liter (95% CI, ؊4.8, ؊2.4 PFU per liter) for MSCs. Within WWTPs, correlations exist between mean NoV GI and NoV GII influent concentrations and between the mean log 10 reduction in NoV GII and the mean log 10 reduction in MSCs.H uman norovirus (NoV) is the leading cause of food-associated gastroenteritis in the United States (1) and Canada (2). U.S. residents are estimated to experience five episodes of norovirus gastroenteritis in their lifetimes (3). NoV is primarily spread via the fecal-oral route. However, attribution of a particular case of NoV illness to a specific source is complex. The transmission may be direct (person to person) or indirect (via contact with contaminated fomites) or may occur through the ingestion of contaminated food or water (4). Noroviruses are genetically diverse, comprising six genogroups (5), three of which (genogroup I [GI], GII, and GIV) are capable of causing illness in humans (6).Among foodborne NoV outbreaks, bivalve molluscs (e.g., clams, oysters, mussels), leafy vegetables, and fruits are the most frequently implicated (7). More than half of the norovirus outbreaks attributed to the consumption of bivalve molluscs in the United States during the years from 2001 to 2008 are believed to have originated from contamination during production or processing (7). Bivalve molluscan shellfish typically grow in estuaries, which may contain NoV-contaminated human fecal material from municipal wastewater outfalls, combined sewer overflow, or nonpoint sources of pollution, including human waste discharged from marine vessels (8, 9). Bivalve molluscan shellfish feed on algae from the surrounding water. During this feeding process, each bivalve mollusc may filter 20 to 90 liters of water per day and bioaccumulate a variety of microorganisms, including viruses and bacteria that are associated with pollution sources (8,(10)(11)(12). Significantly, molluscan shellfish have been found to retain viruses to a greater extent and for much longer periods than they do bacteria (8,13,14). Bivalve molluscs, therefore, may become contaminated with NoV when they are grown in harvesting areas contaminated with human wastes.In the United States and in Canada, ar...

Vibrio parahaemolyticus is a leading cause of seafood-borne gastroenteritis worldwide. Virulence is commonly associated with the production of two toxins, thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH). Although the majority of clinical isolates produce TDH and/or TRH, clinical samples lacking toxin genes have been identified. In the present study, we investigated the effects of V. parahaemolyticus on transepithelial resistance (TER) and paracellular permeability in Caco-2 cultured epithelial cells. We found that V. parahaemolyticus profoundly disrupts epithelial barrier function in Caco-2 cells and that this disruption occurs independently of toxin production. Clinical isolates with different toxin genotypes all led to a significant decrease in TER, which was accompanied by an increased flux of fluorescent dextran across the Caco-2 monolayer, and profound disruption of actin and the tight junction-associated proteins zonula occludin protein 1 and occludin. Purified TDH, even at concentrations eightfold higher than those produced by the bacteria, had no effect on either TER or paracellular permeability. We used lactate dehydrogenase release as a measure of cytotoxicity and found that this parameter did not correlate with the ability to disrupt tight junctions. As the effect on barrier function occurs independently of toxin production, we used PCR to determine the toxin genotypes of V. parahaemolyticus isolates obtained from both clinical and environmental sources, and we found that 5.6% of the clinical isolates were toxin negative. These data strongly indicate that the effect on tight junctions is not due to TDH and suggest that there are other virulence factors.

In an effort to understand the relationship between Vibrio and vibriophage populations, abundances of Vibrio spp. and viruses infecting Vibrio parahaemolyticus (VpVs) were monitored for a year in Pacific oysters and water collected from Ladysmith Harbor, British Columbia, Canada. Bacterial abundances were highly seasonal, whereas high titers of VpVs (0.5 ؋ 10 4 to 11 ؋ 10 4 viruses cm ؊3 ) occurred year round in oysters, even when V. parahaemolyticus was undetectable (<3 cells cm ؊3 ). Viruses were not detected (<10 ml ؊1 ) in the water column. Host-range studies demonstrated that 13 VpV strains could infect 62% of the V. parahaemolyticus strains from oysters (91 pairings) and 74% of the strains from sediments (65 pairings) but only 30% of the water-column strains (91 pairings). Ten viruses also infected more than one species among V. alginolyticus, V. natriegens, and V. vulnificus. As winter approached and potential hosts disappeared, the proportion of host strains that the viruses could infect decreased by ϳ50% and, in the middle of winter, only 14% of the VpV community could be plated on summer host strains. Estimates of virus-induced mortality on V. parahaemolyticus indicated that other host species were required to sustain viral production during winter when the putative host species was undetectable. The present study shows that oysters are likely one of the major sources of viruses infecting V. parahaemolyticus in oysters and in the water column. Furthermore, seasonal shifts in patterns of host range provide strong evidence that the composition of the virus community changes during winter.Viral infection of marine microbial communities (reviewed in references 17, 49, 63, and 64) has been associated with reduced primary production (23, 47, 50) and increased bacterial mortality through either lytic (21,39,42,46,62) or temperate (27,28,39,59,60) phage. Frequently, Vibrio spp. and vibriophage, which are common in seawater (4, 53) and easily culturable (16), have served as model systems in studies of host-virus interactions in the water column (see, for example, references 22, 33, 37, 43, 52, 54, and 61). Vibrio spp. are typically much more abundant in sediments (10 4 g Ϫ1 ) (41), plankton (10 9 g Ϫ1 ) (31), and shellfish (10 5 g Ϫ1 ) (1) than in the water column (ϳ10 ml Ϫ1 ) (5). In contrast, even though virus particles are extremely abundant in sediments (10 8 to 10 9 ml Ϫ1 ) (10, 15) and in the water column (ca. 10 7 to 10 8 ml Ϫ1 ) (64), vibriophage are most abundant in mollusks (10 5 to 10 8 g Ϫ1 ) (3, 14), relatively rare in the water column (ϳ2 ml Ϫ1 ) (34), and frequently undetectable in sediments.The marine bacterium Vibrio parahaemolyticus is a gastrointestinal pathogen that is abundant (10 4 g Ϫ1 ) (12) in oysters. It can cause disease in humans that consume raw shellfish, and in 1997 it was responsible for a major outbreak of disease in British Columbia (6). High abundances of viruses that infect V. parahaemolyticus (VpVs; 10 6 g Ϫ1 ) (3) also occur in oysters.However, with the exception of a study...

There has been a steady increase in illness incidence of Vibrio parahaemolyticus (Vp). The majority of illnesses are associated with consumption of raw oysters. In the summer of 2015, Canada experienced the largest outbreak associated with the consumption of raw oysters harvested from British Columbia (BC) coastal waters. Case investigation of laboratory-confirmed cases was conducted to collect information on exposures and to assist traceback. Investigations at processors and oyster sampling were conducted. Eighty-two laboratory-confirmed cases of Vp infection were reported between January 1 and October 26, 2015. The majority of the cases were reported in BC, associated with consumption of raw BC oysters in restaurants. Sea surface temperatures were above the historical levels in 2015. This outbreak identified the need to improve surveillance and response to increases in human cases of Vp. This is of particular importance due to the potential for increasing water temperatures and the likelihood of additional outbreaks of Vibrio.

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