Paralytic shellfish poisoning (PSP) is caused by saxotoxin produced by dinoflagellates during red tides. Symptoms include gastrointestinal upset, neurological symptoms, and shortness of breath. Shellfish harvesting is prohibited during red tide warnings to protect consumers.
Paralytic shellfish poisoning (PSP) is a serious medical condition caused by ingestion of saxotoxin, a toxin produced by certain dinoflagellates that are especially abundant during periods of algal blooms known as red tides. This condition cannot be cured but can sometimes be managed with the help of supportive care which can increase the chances of recovery. In elderly or immunocompromised people, the risk of death from paralytic shellfish poisoning is greatly increased.
The dinoflagellates responsible for PSP are particularly abundant during red tides because they feed on the algae that proliferate during a red tide. If the algae bloom is driven ashore, the dinoflagellates can open up in the surf, releasing their saxotoxin into the water. When filter feeders such as shellfish ingest saxotoxin, they sequester it in their bodies, meaning that when another organism eats the shellfish, it also ingests the toxin.
Bivalves such as oysters, clams and mussels are especially dangerous during a red tide. However, the innards of shellfish such as crabs and lobsters can also be dangerous. When humans ingest enough saxotoxin, symptoms appear within two hours and often as early as 30 minutes; if symptoms of paralytic shellfish poisoning emerge, medical attention is strongly recommended. Leftover shellfish, if any, should be taken to the hospital with the victim if requested, and otherwise discarded; the toxin cannot be destroyed by freezing or heat, so seafood is unsafe to eat.
Typically, the first sign is a gastrointestinal upset, such as vomiting, nausea, cramping, and diarrhea. Neurological symptoms such as slurred speech, difficulty walking, lack of coordination, tingling or burning sensations, and dizziness follow shortly thereafter. When someone starts experiencing shortness of breath, it indicates that the toxin has started affecting the muscles that help people breathe, and the paralytic shellfish poisoning has become extremely severe.
Fortunately, a number of measures are in place to protect consumers from paralytic shellfish poisoning. During times of red tide, shellfish and shellfish harvesting is generally prohibited and will not resume until extensive testing has concluded that the fish is safe again. When a red tide warning is in effect, signs are often posted on beaches to warn people of the fact, and warnings may be broadcast on the radio or even published in newspapers to ensure that everyone is aware of the situation.
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