Ecology and Control of Pathogenic Strains of Vibrio Vulnificus and Vibrio Parahaemolyticus in U.S. Gulf Coast Oysters

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Raw shellfish (oysters) are an important cause of foodborne disease, and two naturally occuring microorganisms (Vibrio vulnificus and Vibrio parahaemolyticus) are often the cause of these illnesses. This project will improve our understanding of the ecology of pathogenic Vibrio parahaemolyticus and Vibrio vulnificus in raw shellfish and the efficacy of proposed control strategies.
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Seafood is responsible for 26.5% of all U.S. foodborne disease outbreaks, and many more cases, with the majority of these associated with the consumption of contaminated raw bivalve molluscan shellfish. Of particular concern are the pathogenic Vibrio species, including V. vulnificus and V. parahaemolyticus, which cause a variety of syndromes ranging from mild to severe gastrointestinal disease, to a rare but frequently fatal primary septicemia. Most of these illnesses are attributable to the consumption of contaminated U.S. Gulf Coast harvests. Complex epidemiological, ecological, and control issues have served as the impetus for recent national and international risk assessment efforts focused on the pathogenic Vibrio species. These risk assessment documents have identified a variety of data gaps and uncertainties, which we will attempt to address in the proposed work. Therefore, our purpose is to understanding of the ecology of pathogenic Vibrio parahaemolyticus and Vibrio vulnificus in raw molluscan shellfish and the efficacy of representative control strategies. The underlying hypothesis is that there are strain to strain differences in V. vulnificus and V. parahaemolyticus with respect to ecology, prevalence, and virulence. Our study site consists of 4 separate Louisiana harvesting locations that remain open throughout the year. Our approach is a combination of microbiological and epidemiological methods. From an epidemiological perspective, we will interview oyster harvesters and processors to record responses to survey questions concerning actual industry practices with respect to product handling from farm to first receiver. For each sampling event, both water and shellfish will be collected. Water samples will be assayed for environemental parameters including temperature, salinity, turbidity, dissolved oxygen, and pH; both waters and shellfsih will be analyzed microbiologically to determine the levels of total estuarine bacteria, total V. vulnificus and V. parahaemolyticus, and the proportion of pathogenic subtypes of V. vulnificus and V. parahaemolyticus, using a combination of classic cultural methods and molecular biological approaches. We will then investigate potential associations between environmental/ecological factors and total and pathogenic strains of V. parahaemolyticus and V. vulnificus using multivariate logistic regression. Finally, using naturally occuring strains that have been characterized in the previous objectives, we will investigate strain to strain differences in growth and survival, as well as the efficacy of potential mitigation strategies, on the prevalence and levels of pathogenic Vibrios in shellfish. By addressing knowledge gaps and uncertainties previously identified in risk assessments, we intend to provide science-based data that can be incorporated into future risk assessment iterations and upon which food safety policy decisions can be based.