The so-called paralytic mollusc - also known as paralytic mollusc syndrome or PSP - Paralytic Shellfish Poisoning - is a food poisoning caused by the ingestion of contaminated molluscs, which have accumulated saxitoxin and / or its degradation products.
The molluscs accumulate saxitoxin by filtering water containing toxic algal cells, in particular some microalgae (red tide). Even certain crustaceans, such as lobsters, can accumulate algal toxins.
In temperate waters, saxitoxin is produced from algal species belonging to the phylium of dinoflagellates, in particular Gymnodinium catenatum, Alexandrium tamarense, A. catenella, A. acatenella, A. fundyense and A. minutum . Many of these species also proliferate in the waters of our seas. The Italian legislation has incorporated the European indications that foresee a tolerance limit for PSP toxins in bivalve molluscs of 800 µg / kg.
Oysters, mussels, sea scallops and other molluscs of the genus Pecten are the foods most at risk. Being thermostable, saxitoxin is not destroyed by cooking. The saxitoxina can also be accumulated in the meat of fish that feed on contaminated molluscs; in this case the removal of the entrails prevents episodes of intoxication.
The effects of saxitoxin are similar to those of botulinum toxin. Therefore, the symptoms of paralytic mollusc syndrome - which appear within 30 min from the ingestion of contaminated species - include vomiting, diarrhea, ataxia and paraesthesia (tingling, numbness or burning) of the lips, tongue and extremities of the fingers. In very serious cases, cardiovascular collapse and respiratory failure can occur. The reported mortality rate varies from 1 to 22%. In about 50% of patients who survive intoxication, asthenia and partial memory loss remain for about three weeks.
Currently there is no specific antidote capable of neutralizing saxitoxin; therefore, therapy remains essentially symptomatic to combat respiratory paralysis, and may include gastric lavage. Since the toxin is unstable in an alkaline environment, the administration of sodium bicarbonate is useful. In the most serious cases, intubation and mechanical ventilation are used.
