Shellfish poisoning is caused by a group of toxins elaborated by
(dinoflagellates, in most cases) upon which
the shellfish feed. The toxins are accumulated and sometimes
metabolized by the shellfish.
The 20 toxins responsible for
paralytic shellfish poisonings
are all derivatives of saxitoxin.
is presumably caused by okadaic acid, the
dinophysis toxins, the pectenotoxins, and yessotoxin.
shellfish poisoning (NSP)
is the result of exposure to a group
of polyethers called brevetoxins.
Amnesic shellfish poisoning
is caused by the unusual amino acid, domoic acid, as the
contaminant of shellfish.
Ingestion of contaminated shellfish results in a wide variety of
symptoms, depending upon the toxins(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. Less well
characterized are the symptoms associated with DSP, NSP, and ASP.
DSP is primarily observed as a generally mild gastrointestinal
disorder, i.e., nausea, vomiting, diarrhea, and abdominal pain
accompanied by chills, headache, and fever. Both gastrointestinal
and neurological symptoms characterize NSP, including tingling and
numbness of lips, tongue, and throat, muscular aches, dizziness,
reversal of the sensations of hot and cold, diarrhea, and vomiting.
ASP is characterized by gastrointestinal disorders (vomiting,
diarrhea, abdominal pain) and neurological problems (confusion,
memory loss, disorientation, seizure, coma).
Diagnosis of shellfish poisoning is based entirely on observed
symptomatology and recent dietary history.
All shellfish (filter-feeding molluscs) are potentially toxic.
However, PSP is generally associated with mussels, clams, cockles,
and scallops; NSP with shellfish harvested along the Florida coast
and the Gulf of Mexico; DSP with mussels, oysters, and scallops,
and ASP with mussels.
Good statistical data on the occurrence and severity of
shellfish poisoning are largely unavailable, which undoubtedly
reflects the inability to measure the true incidence of the
disease. Cases are frequently misdiagnosed and, in general,
infrequently reported. Of these toxicoses, the most serious from a
public health perspective appears to be PSP. The extreme potency of
the PSP toxins has, in the past, resulted in an unusually high
Symptoms of the disease develop fairly rapidly,
within 0.5 to 2 hours after ingestion of the shellfish, depending
on the amount of toxin consumed. In severe cases respiratory
paralysis is common, and death may occur if respiratory support is
not provided. When such support is applied within 12 hours of
exposure, recovery usually is complete, with no lasting side
effects. In unusual cases, because of the weak hypotensive action
of the toxin, death may occur from cardiovascular collapse despite
Onset of this disease occurs within a few minutes to
a few hours. Duration is fairly short, from a few hours to several
days. Recovery is complete with few after effects; no fatalities
have been reported.
Onset of the disease, depending on the dose of toxin
ingested, may be as little as 30 minutes to 2 to 3 hours, with
symptoms of the illness lasting as long as 2 to 3 days. Recovery is
complete with no after effects; the disease is generally not life
The toxicosis is characterized by the onset of
gastrointestinal symptoms within 24 hours; neurological symptoms
occur within 48 hours. The toxicosis is particularly serious in
elderly patients, and includes symptoms reminiscent of Alzheimer's
disease. All fatalities to date have involved elderly patients.
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