Vibrio parahaemolyticus (Vp) and Oysters
Gulf Coast oysters (Crassostrea virginica
), especially raw oysters on the half shell, top the list of favorites for many diners. Although these bivalves are safe for most people to eat, some consumers should avoid eating raw or undercooked seafood including oysters. These "at risk" consumers include diabetics, individuals that have liver disease and hemochromatosis (iron overload) and anyone with a weakened immune system. Oysters are filter-feeding animals and they sometimes accumulate large numbers of bacteria and viruses, including naturally occurring, disease-causing bacteria such as Vibrio parahaemolyticus
), as they filter the water for their microscopic food.
This potential bacterial presence calls for simple safety steps such as keeping the oysters refrigerated or on ice after harvesting, and washing hands thoroughly with warm, soapy water after handling raw oysters and other raw seafood. If oysters containing naturally occurring bacteria such as Vp
are harvested and not refrigerated or kept on ice, elevated temperatures (greater than 15C or 59F) will allow the Vp
to grow to high levels. Vp
in high enough densities can cause diarrhea and vomiting in consumers who eat raw oysters, especially in those "at-risk" individuals with pre-existing health problems.
To the right are three images showing the most recent scenarios of Vp
risk. Risk scenarios show predicted abundance of Vp
cells in oysters at harvest (top image) and at retail if placed under conventional refrigeration or on ice within the given amount of time (middle and bottom images). The level at which consumers may become ill, i.e., the "infective dose") has been estimated by a U.S. Food and Drug Administration Vp
risk analysis study to be 1,000,000 Vp
cells. This level is listed in the FDA's "Bad Bugs" available here
Risk scenarios are typically updated weekly from satellite imagery. For the GeoTIFF image, click on the link below the image or you can view it in our GIS Mapserver
. Archived images
are also available. For SST and salinity images, see Science Background