Neurotoxic Shellfish Poisoning (NSP) is a condition caused by the ingestion of brevetoxin, a neurotoxin which is secreted by certain dinoflagellates, microscopic marine organisms which can be found all over the world. Most brevetoxin is generated by Karenia brevis, a dinoflagellate which favors the Gulf of Mexico. This condition is closely associated with Paralytic Shellfish Poisoning (PSP), a much more serious condition which is also caused by exposure to a marine toxin.
In Neurotoxic Shellfish Poisoning, symptoms usually appear from within one to three hours of ingestion of the toxin. The patient may experience numbness, tingling, and gastrointestinal distress as the body processes the toxin. Death from Neurotoxic Shellfish Poisoning is extremely rare, unless a patient is already in a state of compromised health. Treatment focuses on supportive care to help the patient feel comfortable.
This condition is linked specifically with consumption of shellfish because shellfish are filter feeders, so they tend to bioaccumulate any harmful toxins in the waters around them. However, Neurotoxic Shellfish Poisoning is also linked more generally with the consumption of seafood, and it can be harmful to birds and marine mammals in addition to human shellfish fans.
Brevetoxin is closely linked with the algal blooms known as red tides. Dinoflagellates and diatoms use the red tide to feed, taking advantage of the proliferation of algae. If these organisms are pushed towards the shore, they often break open in the surf, releasing their toxic payload, which means that any shellfish in the area will ingest the toxin. This is why the consumption of shellfish in a region where a red tide event is occurring is not recommended.
Cases of Neurotoxic Shellfish Poisoning have been documented in Florida and around the Gulf of Mexico since at least the 1800s. In these areas, when a red tide occurs, the harvesting and consumption of shellfish and crustaceans is banned until the event is over, and testing has confirmed that it is safe to eat shellfish again. Because brevetoxin cannot be eliminated through cooking or freezing, if a shellfish meal makes someone in the household sick, the leftovers should be discarded.