Occurrence of Vibrio parahaemolyticus and Related Hemolytic Vibrios in Marine Environments of Washington State 1

ABSTRACTVibrio parahaemolyticusandVibrio vulnificuscan grow rapidly in shellfish subjected to ambient air conditions, such as during intertidal exposure. In this study, levels of total and pathogenic (tdh+and/ortrh+)V. parahaemolyticusand totalV. vulnificuswere determined in oysters collected from two study locations where intertidal harvest practices are common. Samples were collected directly off intertidal flats, after exposure (ambient air [Washington State] or refrigerated [New Jersey]), and after reimmersion by natural tidal cycles. Samples were processed using a most-probable-number (MPN) real-time PCR method for total and pathogenicV. parahaemolyticusorV. vulnificus. In Washington State, the mean levels ofV. parahaemolyticusincreased 1.38 log MPN/g following intertidal exposure and dropped 1.41 log MPN/g after reimmersion for 1 day, but the levels were dependent upon the container type utilized. PathogenicV. parahaemolyticuslevels followed a similar trend. However,V. vulnificuslevels increased 0.10 log MPN/g during intertidal exposure in Washington but decreased by >1 log MPN/g after reimmersion. In New Jersey, initial levels of all vibrios studied were not significantly altered during the refrigerated sorting and containerizing process. However, there was an increase in levels after the first day of reimmersion by 0.79, 0.72, 0.92, and 0.71 log MPN/g for total,tdh+andtrh+V. parahaemolyticus, andV. vulnificus, respectively. The levels of all targets decreased to those similar to background after a second day of reimmersion. These data indicate that the intertidal harvest and handling practices for oysters that were studied in Washington and New Jersey do not increase the risk of illness fromV. parahaemolyticusorV. vulnificus.IMPORTANCEVibrio parahaemolyticusandVibrio vulnificusare the leading causes of seafood-associated infectious morbidity and mortality in the United States.Vibriospp. can grow rapidly in shellfish subjected to ambient air conditions, such as during periods of intertidal exposure. When oysters are submersed with the incoming tide, the vibrios can be purged. However, data on the rates of increase and purging during intertidal harvest are scarce, which limits the accuracy of risk assessments. The objective of this study was to help fill these data gaps by determining the levels of total and pathogenic (tdh+and/ortrh+)V. parahaemolyticusandV. vulnificusin oysters from two locations where intertidal harvest practices are common, using the current industry practices. The data generated provide insight into the responses ofVibriospp. to relevant practices of the industry and public health, which can be incorporated into risk management decisions.

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Nested spatial and temporal modeling of environmental conditions associated with genetic markers of Vibrio parahaemolyticus in Washington state Pacific oysters

10.1101/2022.01.03.471994 ◽

2022 ◽

Author(s):

Brendan Fries ◽

Benjamin J. K. Davis ◽

Anne E. Corrigan ◽

Angelo DePaola ◽

Frank C. Curriero

Keyword(s):

Surface Water ◽

Water Temperature ◽

Genetic Markers ◽

Environmental Conditions ◽

Vibrio Parahaemolyticus ◽

Washington State ◽

Surface Water Temperature ◽

Pacific Oysters ◽

Non Linear ◽

Environmental Measures

The Pacific Northwest (PNW) is one of the largest commercial harvesting areas for Pacific oysters (Crassostrea gigas) in the United States. Vibrio parahaemolyticus, a bacterium naturally present in estuarine waters, accumulates in shellfish and is a major cause of seafood-borne illness. Growers, consumers, and public-health officials have raised concerns about rising vibriosis cases in the region. V. parahaemolyticus genetic markers (tlh, tdh, trh) were estimated using an MPN-PCR technique in Washington State Pacific oysters regularly sampled between May and October from 2005 to 2019 (N=2,836); environmental conditions were also measured at each sampling event. Multilevel mixed-effects regression models were used to assess relationships between environmental measures and genetic markers as well as genetic marker ratios (trh:tlh, tdh:tlh, and tdh:trh), accounting for variation across space and time. Spatial and temporal dependence were also accounted for in the model structure. Model fit improved when including environmental measures from previous weeks (1-week lag for air temperature, 3-week lag for salinity). Positive associations were found between tlh and surface water temperature, specifically between 15°C and 26°C, and between trh and surface water temperature up to 26°C. tlh and trh were negatively associated with 3-week lagged salinity in the most saline waters (> 27 ppt). There was also a positive relationship between tissue temperature and tdh, but only above 20°C. The tdh:tlh ratio displayed analogous inverted non-linear relationships as tlh. The non-linear associations found between the genetic targets and environmental measures demonstrate the complex habitat suitability of V. parahaemolyticus. Additional associations with both spatial and temporal variables also suggest there are influential unmeasured environmental conditions that could further explain bacterium variability. Overall, these findings confirm previous ecological risk factors for vibriosis in Washington State, while also identifying new associations between lagged temporal effects and pathogenic markers of V. parahaemolyticus.

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