Nested Spatial and Temporal Modeling of Environmental Conditions Associated with Genetic Markers of Vibrio parahaemolyticus in Washington State Pacific Oysters

Keywords: Vibrio parahaemolyticus, Crassostrea gigas, Pacific oysters, Washington, spatial, temporal, health geography, multilevel modeling
Session Type: Virtual Paper Abstract
Day: Friday
Session Start / End Time: 2/25/2022 11:20 AM (Eastern Time (US & Canada)) - 2/25/2022 12:40 PM (Eastern Time (US & Canada))
Room: Virtual 36

Abstract

The Pacific Northwest 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. 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. Spatial and temporal variation and 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 temp, 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). A positive relationship between tissue temperature and tdh was observed only above 20°C. 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 suggest influential unmeasured environmental conditions that could further explain bacterium variability. These findings confirm previous ecological risk factors for vibriosis in Washington State, while also identifying new associations between temporal effects and pathogenic markers of V. parahaemolyticus.