Shellfish Poisoning Definition and Overview
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:
- Amnesic shellfish poisoning (ASP)
- Diarrheal shellfish poisoning (DSP)
- Neurotoxic shellfish poisoning (NSP)
- 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 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||parathesias, 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.
Shellfish Poisoning Treatment
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.
Shellfish Poisoning Risk Factors and Prevention
A major risk factor for shellfish poisoning is eating shellfish that has recently been associated with "red tide," a situation where plankton grow so rapidly, its massive numbers of organisms turns 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.
Shellfish Poisoning Prognosis
In general, most outcomes, after the symptoms subside, are good. However, the outcomes worsen according to the amount and type of poison ingested. The amnestic and paralytic poisons, when ingested in large amounts may cause permanent damage to the nervous system or even death.
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Medically reviewed by Joseph Palermo, D.O.; American Osteopathic Board Certified Internal Medicine
Egmond, H.P. Van, M.E., et al. "Marine Biotoxins." FAO.org.
Hinder, s., Hayes, G., Brooks, C., et al. Toxic Marine Microalgae and Shellfish Poisoning in the British Isles; History, Review of Epidemiology and Future Implications. Environ. Health. 10:54, 2011
Silver, M. Protecting Ourselves from Shellfish Poisoning. American Scientist. 94 (4): pp.316–325, 2006
Sobel, J, Painter, J. Illnesses caused by marine toxins. Clin Infect Dis. 41:1290-1296, 2005