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Shellfish Poisoning

Shellfish Poisoning Definition and Overview

Patient Comments

Shellfish poisoning is a general term used to indicate poisoning that occurs when shellfish (mainly oysters, clams, scallops or mussels) are eaten by humans. Shellfish are usually associated with saltwater habitats, but some species inhabit freshwater. Both freshwater and saltwater shellfish may cause poisoning. Because the symptoms of shellfish poisoning are somewhat similar and patients often did not know exactly what type of shellfish they ate, the tendency of the medical community was to simply lump the symptoms together and diagnose "shellfish poisoning" for any shellfish-related problem. However, more recent clinical studies have separated the group of shellfish poisonings into four groups:

  1. Amnesic shellfish poisoning (ASP)
  2. Diarrheal shellfish poisoning (DSP)
  3. Neurotoxic shellfish poisoning (NSP)
  4. Paralytic shellfish poisoning (PSP)

These groups are based on the specific toxins or chemicals that poison humans; they cause specific and nonspecific symptoms. The toxins can accumulate in many different types of shellfish (see above) because the shellfish are filter-feeders and consume marine diatoms and algae that may contain the chemicals. If shellfish consume high levels of the foods that produce the poisons, the shellfish then contain high levels of poison that can be absorbed by humans when they eat the shellfish. In addition, shellfish may concentrate other things such as bacterial and viral pathogens while filter-feeding and transfer these pathogens to people when the shellfish are eaten. These problems are discussed in other articles (for example, Vibrio infections). The goal of this article is to acquaint the reader with shellfish poisonings.

Causes and Symptoms of Shellfish Poisoning

The four major categories of shellfish poisoning are based on the symptoms produced and the specific poisons or pathogens that cause shellfish poisoning. The symptoms appear rapidly, usually within about thirty minutes of eating the poison-containing shellfish. The table below summarizes the symptoms and the poisons that cause them; some researchers consider azaspiracid (see below) a separate type because the symptoms are more serious, others do not. In addition, several textbooks and other articles group all "fish and shellfish toxins" together, so this table represents one organized view of only shellfish poisons.

Shellfish Poisons
Shellfish Poisoning TypeSymptomsCause
Amnesticpermanent short term memory loss, brain damage, deathdomoic acid
Diarrhealdiarrhea, nausea, vomitingokadaic acid, azaspiracid
Neurotoxicslurred speech, nausea, vomitingbrevetoxins
Paralyticparathesias, coordination loss, speech defects, nausea, vomiting, deathsaxitoxin, neosaxiton and gonyautoxins I to IV

Amnestic and paralytic types of poisoning are the most serious types as they can, in a few individuals, cause death. Death from diarrhea or neurotoxic poisoning is rarely, if ever, observed.

Medically Reviewed by a Doctor on 9/30/2016

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Read What Your Physician is Reading on Medscape

Toxicity, Shellfish »

Infectious agents cause most shellfish-associated illness.

Read More on Medscape Reference »


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