Interstate Shellfish Sanitation Conference (ISSC): Vibrio parahaemolyticus in Oysters: Effects of Beach Temperature and Tidal Elevation

Purpose or Scope:

V. parahaemolyticus is implicated in cases of gastroenteritis associated with the consumption of raw or, in some cases, partially cooked shellfish. Outbreaks of V. parahaemolyticus infections involving more than 1,000 confirmed cases of illness associated with consumption of raw shellfish occurred between 1997 and 2006 in the Gulf Coast, Pacific Northwest, Alaska, and Atlantic Northeast regions of the United States. In the State of Washington the number of cases attributed to V. parahaemolyticus increased markedly in 1997 and continued at elevated levels through 2006 (Figure 1). Some of the cases were from recreational shellfish consumption, but the majority were traceable to commercially harvested shellfish. Pacific oysters were the predominant vectors that were implicated.

Approach:

This study involved intensive sampling of multiple stations and several treatment groups in south Puget Sound and Hood Canal to determine levels V. parahaemolyticus and incidences of pathogenic strains in shellfish, sediments, and water under varying tidal regimes, and water and air temperature, and salinity conditions. PSI was responsible for field studies and statistical analyses, the UW School of Aquatic and Marine Science carried out the laboratory analyses. Striking relationships were noted and reported to ISSC between field sampled V. parahaemolyticus and measured environmental parameters.

Progress and Results:

Our ISSC-supported research provided insights into the seasonal increase in V. parahaemolyticus in southern Puget Sound and the increase that occurs within exposed oysters during a tidal cycle. Unfortunately, we do not know why selected sites in Puget Sound had much higher levels of V. parahaemolyticus compared to sites that we would expect to be very similar. More specific to our research in Puget Sound, the levels of V. parahaemolyticus in southern Hood Canal oysters and sediments was much higher compared to the similar samples collected from the southern main basin of Puget Sound. While temperature was a primary factor affecting the population levels and growth rate of this potentially pathogenic bacterium, there were likely other environmental or biological factors to explain the population differences between the two areas in Puget Sound. This work was reported in several national journals, and was followed up with similar results in British Columbia, Canada.

Project Partners:

Back to PSI projects list