Shellfish Toxicity Clinical Presentation

Updated: May 11, 2022
  • Author: Thomas C Arnold, MD, FAAEM, FACMT; Chief Editor: Asim Tarabar, MD  more...
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All 5 shellfish poisoning syndromes can produce symptoms lasting from a few minutes to several hours after ingestion of contaminated shellfish.

Paralytic shellfish poisoning

Symptoms usually begin within 2 hours of eating contaminated shellfish, but can start anywhere from 15 minutes to 10 hours after the meal. [1, 3] The onset generally is noted with paresthesias of the lips, tongue, and gums. After onset, symptoms rapidly progress to involve the distal extremities. Other symptoms include a sensation of floating, headache, ataxia, muscle weakness, paralysis, and cranial nerve dysfunction.

Gastrointestinal symptoms are less common and may include nausea, vomiting, diarrhea, and abdominal pain. Fatalities are usually within the first 12 hours of symptom onset and are caused by unsupported respiratory failure.  PSP usually lasts 3 days, but muscle weakness may persist for weeks.

Neurologic shellfish poisoning

The illness encountered with NSP is milder than that with PSP. Symptom onset ranges from 15 minutes to 18 hours postingestion, and the duration of toxicity ranges from 1-72 hours (usually < 24 h) postingestion.

Presenting symptoms include gastroenteritis; rectal burning; paresthesias of the face, trunk, and limbs; myalgias; ataxia; vertigo; and reversal of hot/cold sensation. Other less common features include tremor, dysphagia, bradycardia, decreased reflexes, and mydriasis.

This syndrome presents much like ciguatera poisoning but without a paralytic component, and it may last from several hours to a few days. The brevetoxins, unlike the other shellfish toxins, can become aerosolized by the surf and produce an allergic response characterized by rhinorrhea, conjunctivitis, bronchospasm, and cough in sensitive individuals along the shore.

Diarrheal shellfish poisoning

DSP produces stomach and intestinal symptoms that usually begin 30 minutes to a few hours after eating contaminated shellfish and include the following [1] :

  • Vomiting
  • Severe diarrhea
  • Nausea
  • Abdominal cramps
  • Chills

Amnestic shellfish poisoning

In most cases, gastrointestinal symptoms such as diarrhea, vomiting, and abdominal pain develop within 24 hours of eating toxic shellfish, followed by headache, memory loss, and cognitive impairment. In severe cases there may be hypotension, arrhythmias, ophthalmoplegia, coma, and death. Survivors may have severe anterograde, short-term memory deficits. [3]

Azaspiracid shellfish poisoning

Azaspiracid Shellfish Poisoning (AZP) is the most recently discovered human illness related to shellfish contaminated with a HAB toxin. AZP is believed to be caused by a dinoflagellate that produces toxins that have been found in Ireland, the Netherlands, Belgium, Morocco, and eastern Canada. [1]  

Eating contaminated shellfish can result in symptoms including the following [1] :

  • Nausea
  • Vomiting
  • Diarrhea
  • Stomach cramps

Physical Examination

Findings vary according to the syndrome involved but volume depletion from gastrointestinal symptoms is common to all syndromes. Gastrointestinal symptoms occur less often in PSP than in the other syndromes. Paresthesias of the face and extremities are noted only in PSP and NSP. ASP is the only shellfish syndrome with cognitive dysfunction as an early finding.