Saxitoxin invades Seattle!

September 4, 2010, 11:25 am

The Seattle Post-Intelligencer reported this week that because of high levels of saxitoxin, waters along the shorelines of King County in Washington have been closed to shellfish harvesting.  The ban includes all mollusks (oysters, clams, mussels, scallops) but not crabs or shrimp.

Saxitoxin is a heat-stable neurotoxin that blocks sodium channels and impairs conduction in excitable nerve, muscle, and myocardial cells.  Mollusks filter and concentrate dinoflagellates — primarily Alexandrium catanella — that actually produce the toxin.  These small organisms proliferate during red tide blooms. Non-traditional (that is, non-filter-feeding) vectors of saxitoxin have been identified, including crustaceans and some fish.

The clinical condition caused by saxitoxin is paralytic shellfish poisoning (PSP). Within an hour of ingesting affected mollusks, patients develop facial paresthesias and bulbar palsy, with dysarthria and dysphagia.  Muscle weakness spreads to the extremities and eventually results in respiratory paralysis.  Cognition remains clear.  Since saxitoxin generally does not cause initial gastrointestinal symptoms, there is no self-decontamination.  There is no antidote for saxitoxin; the mainstay of treatment is support care with mechanical ventilation if needed.

A just-published comprehensive review of PSP is well worth reading for anyone with an interest in the topic.

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