Science & Research

Volume IV - 9.4 Seafood Toxins [Advanced]

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Orientation and Training
Food and Drug Administration

Section 9 - Seafood Chemistry

Shellfish poisoning is caused by a group of toxins elaborated by planktonic algae (dinoflagellates, in most cases) upon which the shellfish feed. The toxins are accumulated and sometimes metabolized by the shellfish. Amnesic shellfish poisoning (ASP) is caused by the unusual amino acid, domoic acid, as the contaminant of shellfish. The 20 toxins responsible for paralytic shellfish poisonings (PSP) are all derivatives of saxitoxin. Diarrheic shellfish poisoning (DSP) is presumably caused by a group of high molecular weight polyethers, including okadaic acid, the dinophysis toxins, the pectenotoxins, and yessotoxin. Neurotoxic shellfish poisoning (NSP) is the result of exposure to a group of polyethers called brevetoxins. FDA only includes ASP and PSP in the current compliance program.

All humans are susceptible to shellfish poisoning. Elderly people are apparently predisposed to the severe neurological effects of the ASP toxin. A disproportionate number of PSP cases occur among tourists or others who are not native to the location where the toxic shellfish are harvested. This may be due to disregard for either official quarantines or traditions of safe consumption, both of which tend to protect the local population.

Ingestion of contaminated shellfish results in a wide variety of symptoms, depending upon the toxin(s) present, their concentrations in the shellfish, and the amount of contaminated shellfish consumed. In the case of PSP, the effects are predominantly neurological and include tingling, burning, numbness, drowsiness, incoherent speech, and respiratory paralysis. ASP is characterized by gastrointestinal disorders (vomiting, diarrhea, abdominal pain) and neurological problems (confusion, memory loss, disorientation, seizure, and coma). Diagnosis of shellfish poisoning is based entirely on observed symptomatology and recent dietary history.

All shellfish (filter-feeding mollusks) are potentially toxic. However, PSP is generally associated with mussels, clams, cockles, and scallops; and ASP with mussels.

[The foregoing was adapted from the “Bad Bug Book: Foodborne Pathogenic Microorganisms and Natural Toxins Handbook,” U.S. Food & Drug Administration, CFSAN, on-line at:]

Laboratory analysis for marine toxins is restricted to specialized FDA field laboratories. Therefore training in this area is up to the discretion of each servicing laboratory. Laboratories may contact the Seafood Products Research Center, co-located with Pacific Regional Laboratory Northwest and Seattle District, for additional guidance and training suggestions.

Page Last Updated: 03/18/2016
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