Paralytic shellfish poisoning

Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks (such as mussels, clams, oysters and scallops). These shellfish are filter feeders and, therefore, accumulate neurotoxins, called Saxitoxin, produced by microscopic algae, such as dinoflagellates, diatoms, and cyanobacteria. Dinoflagellates of the genus Alexandrium (genus) are the most numerous and widespread saxitoxin producers and are responsible for PSP blooms in subarctic, temperate, and tropical locations. The majority of toxic blooms have been caused by the morphospecies Alexandrium catenella, Alexandrium tamarense, and Alexandrium fundyense, which together comprise the A. tamarense species complex. In Asia, PSP is mostly associated with the occurrence of the species Pyrodinium bahamense. Human toxicity and mortality can occur after ingestion of these animals, but toxicity is also seen in wild animal populations.

Also some pufferfish, including Chamaeleon puffer, contain saxitoxin, making their consumption hazardous.

Pathophysiology
The toxins responsible for most shellfish poisonings are water-insoluble, heat and acid-stable, and ordinary cooking methods do not eliminate the toxins. The principal toxin responsible for PSP is saxitoxin. Some shellfish can store this toxin for several weeks after a harmful algal bloom passes, but others, such as butter clams, are known to store the toxin for up to two years. Additional toxins are found, such as neosaxiton and gonyautoxins I to IV. All of them act primarily on the nervous system.

PSP can be fatal in extreme cases, particularly in immunocompromised individuals. Children are more susceptible. PSP affects those who come into contact with the affected shellfish by ingestion. Symptoms can appear ten to 30 minutes after ingestion, and include nausea, vomiting, diarrhea, abdominal pain, tingling or burning lips, gums, tongue, face, neck, arms, legs, and toes. Shortness of breath, dry mouth, a choking feeling, confused or slurred speech, and loss of coordination are also possible.

PSP in wild marine mammals
PSP has been implicated as a possible cause of sea otter mortality and morbidity in Alaska, as one of its primary prey items, the butter clam (Saxidonus giganteus) bioaccumulates saxitoxin as a chemical defense mechanism. In addition, ingestion of saxitoxin-containing mackerel has been implicated in the death of humpback whales

Additional cases where PSP was suspected as the cause of death in Mediterranean monk seals (Monachus monachus) in the Mediterranean Sea have been questioned due to lack of additional testing to rule out other causes of mortality.