Shellfish Poisoning

What Is Shellfish Poisoning?

Shellfish poisoning is caused by eating contaminated shellfish, such as oysters, clams, scallops or mussels.
Shellfish poisoning is caused by eating contaminated shellfish, such as oysters, clams, scallops, or mussels.

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 on 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.

What Causes 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 Type Symptoms Cause
Amnestic permanent short term memory loss, brain damage, death domoic acid
Diarrheal diarrhea, nausea, vomiting okadaic acid, azaspiracid
Neurotoxic slurred speech, nausea, vomiting brevetoxins
Paralytic paresthesias, coordination loss, speech defects, nausea, vomiting, death saxitoxin, 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.

What Is the Treatment for Shellfish Poisoning?

There is no specific treatment for shellfish poisoning. However, some health care professionals may induce vomiting or use a stomach pump to remove food if the patient is seen within three hours of ingesting the shellfish.

These actions may reduce the amount of poison that is absorbed through the gastrointestinal tract. In addition, patients are often given IV fluids as they may become dehydrated from vomiting.

The use of oral charcoal may be used in some patients that are seen early after ingestion of large amounts of food likely containing large amounts of shellfish poison. Some health care professionals advise the stomach should be pumped to remove foods before charcoal is administered.

What Are the Risks of Shellfish Poisoning?

A major risk factor for shellfish poisoning is eating shellfish that has recently been associated with "red tide," a situation where plankton grows so rapidly, its massive numbers of organisms turn the water a reddish hue.

Although many health care professionals suggest that people should not eat uncooked shellfish (for example, "raw" oysters) to prevent exposure to bacterial and viral diseases, cooking does not destroy the poisons in contaminated shellfish. There are no antidotes for these shellfish poisons.

Can You Die from Shellfish Poisoning?

In general, most outcomes, after the symptoms subside, are good. However, the outcomes worsen according to the amount and type of poison ingested.

Amnestic and paralytic poisons, when ingested in large amounts, may cause permanent damage to the nervous system or even death.

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