Noroviruses in Coastal Waters: Implications for Seafood Cultivation and Human Health

If you've had stomach flu or food poisoning, there is a good chance you've had a norovirus infection. According to the Centers for Disease Control, 1 in 15 Americans become infected with noroviruses each year, making these highly contagious pathogens the leading cause of foodborne disease outbreaks in United States. This project seeks to determine the fate, transport and human health risk of human noroviruses (NoVs) along the Central California coast, particularly in areas where shellfish are grown commercially or recreationally harvested. To do this, the research team is testing four hypotheses: 1) NoVs are preferentially attached to particles in estuarine and marine waters; 2) NoVs accumulate in mussels; 3) the presence of NoVs is correlated with the presence of zoonotic pathogens, such as Toxoplasma, Cryptosporidium, Giardia and Salmonella, and fecal indicator bacteria; and 4) NoVs pose a significant health risk to those who consume shellfish. In work to date, scientists have conducted laboratory experiments confirming that NoVs do attach to particles in water samples and display patterns of enhanced aggregation in estuarine and marine water samples. Subsequent laboratory experiments have examined the transport characteristics of NoVs and the effects of water salinity on the accumulation of NoVs in coastal habitats. Data analyses from these experiments are ongoing but have implications for understanding the factors that determine NoVs concentrations in waters where shellfish are present. In the field component of their project, researchers have collected water samples from Tomales and Monterey bays and have determined that hollow fiber ultrafiltration is the best technique for collecting NoVs from environmental samples. Mussels have also been collected during the dry season and after rainfall events in the Carmel and Cambria regions. Testing of these samples has documented the presence of Toxoplasma gondii, Giardia and Salmonella in these bivalves. In future work, reverse transcription PCR techniques will be applied to mussel and water samples to quantify NoVs gene expression levels. Results from these analyses will provide the basis for evaluating whether NoVs pose a significant risk to shellfish consumers.