Northwest Fisheries Science Center

Vibrio parahaemolyticus risk assessment in the Pacific Northwest: It's NOT what's in the water

Contributed by Vicky Krikelas March 2019

The big picture

A naturally-occurring marine bacterium, Vibrio parahaemolyticus, can cause gastrointestinal disease and even death in seafood consumers that eat raw shellfish, especially oysters. Outbreaks can occur with little or no warning, leaving managers and shellfish growers little time to react and initiate mitigation measures. Few tools are available to help scientists determine if oysters are at risk of infection by harmful strains of Vibrio parahaemolyticus.

In a recent collaboration with the Washington State Department of Health, NWFSC scientists measured the density of strains with a genetic marker known to be associated with the ability to cause disease, both in oyster tissue and in the surrounding water column. Even when high levels of strains with this marker were present in the water, similar levels were not detected in oyster samples. Scientists concluded that it's not what’s in the water that matters when trying to measure the risk of infection by this Vibrio species, at least for waters in the Puget Sound and off the Washington coast. Instead, there appears to be a consistent seasonal pattern in the probability of presence and in the average density of strains carrying the genetic marker in oysters, which is largely independent of the levels in the water column. Average density in oysters varies across the Puget Sound and the Washington coast, with different patterns across the two years of the study. Frequent testing of oyster tissue from each area for the genetic marker may provide the best indicator for risk of infection.

Why it matters

Vibrio contamination poses a threat to public health and can result in severe economic losses to Washington state's $100M shellfish aquaculture industry and recreational harvest through costly recalls of contaminated shellfish and beach closures. Knowing how to better assess the risk of Vibrio in shellfish can improve our ability to forecast outbreaks and give managers better information for early warnings.

The details

Read the paper

Dig deeper

Learn more about the NWFSC Marine Microbes and Toxins Program’s previous work on Vibrio.