The bacteria Vibrio parahaemolyticus is the leading cause of seafood-borne illness worldwide but has only been a concern in the Northeast U.S. in the last decade since a particularly virulent strain ST36, native to the Pacific, was introduced. ST36 has never been detected in NH and regulators would like to keep it that way, so they prohibit importation of oyster seed from areas with known ST36 outbreaks. This prevents possible introduction, but also limits where NH oyster growers can source their seed. This research builds on prior NH Sea Grant funded work by Dr. Whistler which showed that small seed produced in controlled conditions in hatcheries can have limited Vibrio risk, but the risk of importing larger seed produced in upwellers in estuaries remain unexplored. This research will continue to explore risk of Vibrio introduction through this larger seed and seeks to understand how the microbiome of oysters could both increase vulnerability to Vibrio and provide opportunities for pathogen reduction. The research will also improve assays used to detect Vibrio so that they can discriminate between the problematic ST36 and other harmless strains. This will help provide critical missing data to inform oyster aquaculture policy and help support growers seeking safe seed.
Principle Investigator
Cheryl Whistler, Ph.D.
Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire
Cheryl.Whistler@unh.edu
Project Funding Cycle
2024-2025 NH Sea Grant Biennial Research Funding
Project Abstract
Vibrio parahaemolyticus, the leading cause of seafood-borne gastroenteritis world-wide, has only been a cause for concern in the Northeast US in the last decade due to recent increases in illnesses predominantly caused by a hypervirulent and globally spreading Pacific-native strain called ST36, which has never been detected in New Hampshire despite its persistence in several aquaculture areas to the south. Because New Hampshire State public health officials and shellfish managers recognized ST36 and other pathogenic strains could be translocated into NH via movement of oyster seed, they implemented a groundbreaking policy in 2018 restricting movement of oyster seed from localities with a history of ST36 outbreaks.
Unfortunately, as defensible as this policy is, it has strained NH oyster farmers due to limited availability of seed. Growers and managers in NH hope to see restrictions relaxed but are missing key data on what seed is a risk in order to know how to adapt the policy. Larger seed is particularly concerning because though spawn is produced in hatcheries under conditions that we have confirmed through our current Sea Grant funding substantially limit Vibrio contamination, larger seed is grown-out in estuary nurseries in upwellers often adjacent to commercial adult oyster production sites which could be environmental reservoirs for pathogenic strains. More recently, implementation of the NH policy has even paved the way for managers in other states to consider whether movement of seed should be regulated- especially in light of increasing risk of Vibrio vulnificus contamination which has a higher incidence of serious disease and even death in susceptible individuals. In direct consultation with NH growers and shellfish managers in both NH and MA, we identified a critical need to 1) document the risks of Vibrio introduction associated with oyster seed movement and 2) evaluate whether “salinity relay” commonly used on adult oysters could be adapted to an on-land system to reduce pathogen contamination not only in small oyster spat, but also in larger oyster seed. Now that we have developed capacity for oyster microbiome manipulation using salinity relay as part of previous Sea Grant research, herein we propose to expand our studies to include larger oyster seed which most NH farmers rely upon. As a mechanistic underpinning of our research questions, we seek to understand the association of the oyster microbiome with Vibrio to gain insight into the vulnerability of oysters to contamination and identify opportunities for pathogen reduction. Finally, assessing contamination and its reduction requires accurate and sensitive methods that target pathogens of concern. Currently used FDA enumeration methods are not specific, cross- detect variants of other Vibrio spp., and are unable to discriminate between ST36 and likely non- pathogenic strains that carry similar gene content. Therefore, we propose to also 3) improve assays for use in our region to provide useful information. We also will expand our analyses to include other enumeration platforms that are more widely applicable without specialized equipment. In this project we will balance these research initiatives to provide critical missing data needed to inform policy development by the state and provide contingencies to growers for acquiring safe seedstock and ensuring safe product.
