CFSAN Regulatory Codes: VI, A-H
CFSAN Program Priority Codes: 1.7b, 1.4g
Start Date: 1/01/98    Completion Date: 9/30/02

Statement of Research Problem:
Illness and death caused by marine vibrios acquired during the consumption of raw molluscan shellfish remain a significant public health problem. Risk assessment is an approach to addressing this problem but it requires knowledge of exposure to virulent organisms. This study was designed to gather information of the exposure of the shellfish-consuming public to both Vibrio vulnificus and V. parahaemolyticus. Further, little is known of the virulence factors associated with V. vulnificus or why V. vulnificus illnesses are linked primarily to oysters harvested from the Gulf coast during the summer. This nationwide survey presented an opportunity to gather strains of V. vulnificus from different coasts and different seasons for use in studies of virulence factors.

Statement of Project Objective(s):
To determine consumer exposure to V. vulnificus and V. parahaemolyticus through consumption of raw oysters, assemble a library of strains of V. vulnificus, and utilize those strains to determine differences in virulence of strains collected from different U.S. coasts during different seasons.

Anticipated Impact on FDA Regulatory Program:

1. Provide data needed for risk assessment.
2. Provide data for use by FDA, functioning within the Interstate Shellfish Sanitation Conference (ISSC), to make decisions on pathogenic Vibrio issues.

Project Priority Changes During FY2000: None

Collaborators:

Interstate Shellfish Sanitation Conference and participating states
National Marine Fisheries Service
FDA/ORA Denver and Atlanta Laboratories

This collaborative study involves OS, ORA, ISSC and NMFS in determining the densities of Vibrio vulnificus and V. parahaemolyticus to which consumers are exposed when eating raw oysters. This project involves collections of consumer samples in nine locations throughout U.S. Samples were analyzed at GCSL and at ORA laboratories. A library of V. vulnificus strains has been assembled to represent isolates from different coasts and seasons. These isolates will be used to determine if strain differences in virulence exist among different strains of V. vulnificus.

1. Gather data useful for risk assessment that represents the density of Vibrio vulnificus and V. parahaemolyticus in raw oysters at the time of consumption. The data was collected in a year long (6/98-7/99) nationwide survey that sampled oysters harvested from different coasts.
2. To determine if there are differences in virulence among strains of V. vulnificus that could account for the relationship of V. vulnificus illnesses to location and time of shellfish harvest.

1. Analyze data for incorporation in risk assessment models for vibrios.
2. Conduct in vitro characterization of selected V. vulnificus strains through extramural contracts.

1. Data collected on 370 lots of oysters between June 1998 and July 1999 was analyzed and a technical report prepared. The report was provided to the OS and to the ISSC which distributed it to its members through its web site (www.ISSC.org). A manuscript is being prepared for submission to a peer-reviewed journal. Data on V. parahaemolyticus densities in retail shellfish was utilized in the V. parahaemolyticus risk assessment.
2. A library of V. vulnificus strains has been assembled this library contains representative strains of V. vulnificus isolated during different seasons and from different coast of the U.S.

1. Conduct in vitro characterization of V. vulnificus strains. This will involve testing a selected number of environmental strains obtained during different seasons and from different coasts by a variety of test to determined if strains can be distinguished from or related to pathogenic strains of V. vulnificus. GCSL is providing the strains, coordinating the testing and interpreting the results. The ISSC is funding various laboratories to test 50 strains for virulence factors (LPS, ViuB gene, RAPD-PCR, capsule, plasmids and mouse LD₅₀).

1. In vitro characterization of a large number of V. vulnificus strains from the assembled library. Results from the FY 2001 deliverable will determine the level at which this research needs to be pursued. Extramural funds will be needed to continue this research.