Shellfish Poisonings (NSP and PSP)
Neurotoxic shellfish poisoning (NSP) is caused by a marine toxin present in contaminated shellfish. Brevetoxins produced by a marine algae, Karenia brevis (K. brevis), may accumulate when filter-feeding shellfish are exposed to algal blooms or red tide events.
The bi-products produced by the brevetoxins are able to cause human and wildlife illnesses. Brevetoxins are not destroyed by heating or freezing methods, so even well-cooked shellfish may transmit the toxin. The toxin is odorless and tasteless and cannot be detected by taste or smell. Transmission is foodborne. NSP is not transmitted person-to-person.
Infections may result from ingesting contaminated shellfish that has been harvested from an area with K. brevis cells and brevetoxins present in the water.
NSP cases have been associated with consumption of clams, mussels, scallops, oysters, whelks,
coquinas and certain gastropods. These molluskan shellfish are filter feeders that can filter large amounts of the red tide algae from
the water and concentrate the toxin producing algae in their gut.
Shellfish harvested from red tide areas should not be eaten. Other
seafood also commonly called shellfish such as crabs, shrimp, and lobster
can be eaten because they do not filter water and will not concentrate the
toxin. Scallops can be eaten if only the scallop muscle is eaten, as is
normally the case. Scallop stew, which would use the whole animal, should
not be eaten.
Paralytic shellfish poisoning (PSP) is caused by a different marine toxin called saxitoxin.
PSP is also transmitted by shellfish consumption. Implicated shellfish include: mussels, surf clams, softshell clams, sea scallops, butter clams, ocean quahogs, oysters, gastropods, geoduck, cockles, lobsters, crabs, and, rarely, toxic fish. PSP cases have been previously reported in California, Oregon, Washington, Alaska, Maine, Massachusetts, and Washington.
Puffer fish caught in Florida waters, such as the Indian River Lagoon, have been found to contain the same naturally-occurring saxitoxin that found in some shellfish. Whether contained in shellfish or in Southern puffer fish, saxitoxin can cause serious paralytic illness if eaten. If you suspect that you have either NSP, PSP, or saxitoxin fish poisoning, contact your local County Health Department or the Florida Poison Control Hotline at: (800)-222-1222. Seek medical treatment from a health care provider.
NSP in Florida
NSP outbreaks were reported in 1995, 1996, 2001, 2005, and 2006 along the southwest Florida coast, with the majority of cases occurring in Lee County. The majority of NSP cases were associated with consuming recreationally harvested clams during the summer months.
Past NSP cases were associated with illegal recreational shellfish harvesting. To reduce the risk of contracting NSP, avoid consuming shellfish that was harvested from beds impacted by a red tide or any shellfish harvested in unapproved or closed shellfish beds.
Neurotoxic Shellfish Poisoning Article (359 KB pdf
Dr. Sharon Watkins, Andrew Reich, Dr. Lora Fleming, and Dr. Roberta Hammond, Marine Drugs 6(3):431-55
NSP Power Point Presentation (1 MB pdf
Red Tides in North Florida Seminar: Ecology, Impacts and Response Activities
Dr. Roberta Hammond
Red Tide Management for Shellfish Harvesting Areas (503 KB pdf
Joe Shields III and Chris Brooks
Saxitoxin Fish Poisoning Poster-Eat Puffer and You May Suffer (632 KB pdf
Florida Department of Health, Food and Waterborne Disease Program
Return to the Aquatic Toxins Disease Prevention Program Home Page