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Harvest and Post-Harvest Processing Conditions Conducive to Reduced Levels of Pathogenic Vibrios in Oysters


The goal of this project is to gain a better understanding of the ecology of pathogenic vibrio bacteria in the estuarine waters of coastal New Hampshire. Building on previous studies from the 1990's, recent work has shown the incidence of Vibrio parahaemolyticus and Vibrio vulnificus in shellfish has increased and for longer time periods, along with the presence of low concentrations of strains with virulence genes. We intend to use recently adopted molecular methods for detecting pathogenic vibrio species and their virulent strains for more in-depth study of the underlying mechanisms that affect vibrio populations in shellfish and harvest areas, with a particular focus on refining low-cost processing strategies (i.e., relaying) to eliminate pathogenic vibrios from bivalve mollusks. More in-depth studies on both processing strategies and harvest area conditions are needed to accomplish these goals. <P>The specific objectives for the project are as follows: 1. Develop, refine and apply methods for detection and enumeration of V. parahaemolyticus and V. vulnificus and their virulence genes in the Great Bay Estuary. 2. Determine environmental and biological factors associated with reduced concentrations of pathogenic vibrios in freshly harvested and post-harvest processed oysters. <P>The expected outputs for this project include conducting an intensive ecological assessment of the presence of pathogenic vibrios in estuarine ecosystems under a wide range of environmental conditions. This ecological assessment will be complimented by controlled experiments on shellfish processing strategies, especially relaying, to remove the vibrios and thus reduce the public health threat associated with consuming raw shellfish. Graduate and undergraduate students will learn research and analytical methods through direct involvement in this project. <P>The project will also help to foster continued collaborations with academic colleagues at UNH and other institutions, and with the local and national seafood industry and public health agencies. The proposed project findings will be used to inform regional and state shellfish and beach managers about the conditions that are associated with reduced vibrio concentrations. The utility of the developed detection methods will also be discussed with these same managers to help them decide how to conduct any analyses for vibrios that may be required in the near future. <P>The shellfish aquaculture and grower industry will also be informed through state and regional organizations about the ecosystem assessment and the PHP strategies study findings to provide safe shellfish to consumers and to begin consideration of PHP strategies that may loom as requirements in the future. The study results will also be used to help protect public health in the local and regional areas through educational and extension efforts.

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Non-Technical Summary: The focus of this research is to test strategies for removing disease-causing bacteria from shellfish to diminish the risk of gastroenteritis and death in humans when consuming raw or undercooked oysters. Gastroenteritis infections caused by Vibrio parahaemolyticus (Vp) and death in certain health-compromised individuals caused by Vibrio vulnificus (Vv) are typically associated with shellfish from warmer areas like the Gulf of Mexico. Recent VP outbreaks in the more northern Pacific and Atlantic ocean waters of the US are evidence of more widespread infections and have heightened nationwide public health concerns. The US shellfish industry uses several strategies to deplete harvested shellfish of pathogenic microorganisms from sewage pollution, and these same methods, with some modifications and under certain environmental conditions, appear to have potential for removing naturally occurring vibrio bacteria. These results may be significant, as the future for marketing live oysters is threatened by increasing rates of human infections from pathogenic vibrios, and most other post-harvest strategies for treating shellfish result in dead, sterilized oysters. The project also address these public health concerns by assessing ecosystem conditions under which these disease-causing bacteria are favored and therefore present at elevated concentrations, or where they are inhibited and either absent of present at low levels with minimal public health significance. One other public health issue is that not all strains of these bacteria can cause disease. We are therefore testing water, shellfish and sediments for the presence of genes that are associated with infections to determine their incidence and where/when/why they are present. All of these research approaches will help to provide a better understanding of how to manage shellfish harvesting and to treat harvested shellfish to reduce the threat of infections and disease caused by pathogenic vibrios. <P> Approach: We will be using qPCR for detecting both V. parahaemolyticus and V. vulnificus. The methods are from published protocols with modification necessary for adoption by our labs at UNH. The field methods will follow long-established procedures at sites with a wealth of background information on vibrios and environmental conditions. Complimenting this project are several ongoing ecosystem monitoring programs on shellfish and water quality that will benefit from and provide benefits to this project. The most obvious unique aspect of the project is the close collaboration with the local shellfish depuration facility. These facilities are not common, and the collaboration has been ongoing for over 20 years. The use of their facilities allows for the research to be more applied and have direct and immediate relevance. Evaluating depuration and relaying for eliminating vibrios from shellfish is also unique; both are strategies designed for removal of fecal-borne pathogens. The experimental design includes evaluation of the biological and abiotic mechanisms responsible for the reduction in vibrio levels when shellfish are exposed to vibrio-free water, as well as why the water is vibrio-free. No other studies are focusing on the detection of vibrio strains containing virulence genes in the Gulf of Maine, which is critical with oncoming climate changes and warming ocean and estuarine ecosystems. The results will be conveyed through graduate student and departmental seminars at UNH and undergraduate students and adults interested in estuarine science will be involved in the project in the lab and field. Local fisheries extension agents will be involved in the project, and outreach will involve interactions with local and regional shellfish industry organizations and public health agencies. The data collected will include levels of the vibrios in water, shellfish and sediments at sites throughout coastal New Hampshire. Other data will include that describing the results of the shellfish processing strategies evaluation, and the presence/absence of virulence genes. The plan for evaluating success is to have scientifically sound and comprehensive data to serve mainly three uses. These include the data to support management of shellfish harvesting in the Gulf of Maine based on the environmental and ecosystem conditions that favor or inhibit the presence of pathogenic vibrio species. The second use is the conditions under which vibrios can most effectively be eliminated from shellfish once they've been harvested so that the shellfish industry in other areas can use our findings as guidelines for their own evaluations. Last is the use of the results to help asses the public health significance of these bacteria in the Northeast. Present attitudes are that these do not pose much of a threat. The results of this project will be used to help confirm that, or to induce changes in attitudes.

Jones, Stephen
University of New Hampshire
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