Seafood poisoning is food poisoning from ingestion of either marine toxins or contamination associated with bacterial spoilage. Seafood poisoning occurs after a person eats fish or shellfish that contains a toxin made by dinoflagellates or after eating improperly handled seafood. Dinoflagellates are small marine organisms found throughout the oceans, especially in and near coral reefs. The toxins produced by dinoflagellates accumulate in shellfish or move up the food chain as smaller toxin-contaminated fish are eaten by larger fish. Seafood poisoning can be categorized as that associated with fish and that associated with shellfish.

Symptoms of seafood poisoning vary with the toxin ingested and may be gastrointestinal, neurologic, or allergic. Marine toxins are tasteless and odorless and are not affected by cooking or by any other method of food preparation. The risk of seafood poisoning is increasing as more seafood is added to the diet; as the number of toxic algal blooms increase in frequency, intensity, and geographic distribution; and as more people travel to coastal areas and tropical islands and eat local fish and shellfish.

Ciguatera Fish Poisoning

Description

Ciguatera is a term of Spanish origin that originated in the Caribbean basin to describe the poisoning caused by ingesting a marine snail that the early Spanish settlers called cigua. The term is now used to describe the poisoning of a person who has eaten fish contaminated by a dinoflagellate-produced toxin. Large fish become contaminated with the toxin when they eat reef fish that feed on these small organisms.

Occurrence

Ciguatera is a commonly reported marine seafood toxin poisoning. About 50,000 to 100,000 people per year who live in or visit tropical and subtropical regions become ill with ciguatera poisoning. Affected areas lie between and extend slightly beyond the Tropics of Cancer and Capricorn and include the Caribbean Islands, Florida, French Polynesia, American Samoa, Micronesia, Hawaii, and Australia. The following fish have been reported as sources of ciguatera poisoning:

Clinical presentation

Common symptoms of ciguatera poisoning include nausea, vomiting, diarrhea, cramps, excessive sweating, headache, and muscle aches. Sensations of burning or “pins and needles,” especially in the hands and feet, weakness, itching, and dizziness can occur. Some people experience temperature reversals (hot surfaces feel cold and cold surfaces feel hot), unusual tastes, nightmares, or hallucinations. Deaths, although rare, do occur as a result of hypotension and cardiovascular collapse. Symptoms often occur within 3 hours of eating the contaminated fish or shellfish, but they can occur a day or more later. Neurologic symptoms may begin several days later and continue for months. People who have previously had ciguatera poisoning tend to develop more severe symptoms with additional exposures.

A diagnosis of ciguatera poisoning is based on clinical signs and symptoms and on a history of having eaten fish that is known to carry ciguatoxin (1). Laboratory tests have been developed to test for ciguatoxin in fish. Unfortunately there is no test for ciguatoxin in humans.

Prevention

Because no country routinely tests for ciguatoxin in locally caught fish, travelers need to be aware of the areas where the toxin exists and of the local fish that have been associated with the toxin. Ciguatoxin, which does not affect the taste or smell of fish, cannot be destroyed by cooking, smoking, freezing, or any other method of food preparation (2). Large fish (>6 lbs or 13.4 kgs) are more likely to contain ciguatoxin. Thus, refraining from eating large reef fish is protective, as well as not eating fish liver, intestines, heads, and roe, where the toxin is concentrated (2).

Treatment

There is no antidote for the ciguatoxin. Treatment of ciguatera poisoning is generally supportive and tailored to symptoms. Arrhythmias, hypotension, and acute neurologic syndromes require emergency treatment.

Scombroid

Description

Scombroid poisoning results from eating fish that naturally contain high histidine levels and have not been handled or refrigerated properly. When fish are mishandled, contaminating bacteria are able to chemically convert the histidine to histamine, which may cause what is often referred to as a “fish allergy.” The poisoning gets its name from Scombridae, the family of fish most commonly associated with this condition. Yellowfin tuna, mackerel, skipjack, and bonito belong to this family. Some nonscombroid fish (e.g., herring, bluefish, sardine, anchovy, amberjack, black marlin, and mahi-mahi) can also cause scombroid poisoning when they are not handled or refrigerated properly.

Occurrence

Scombroid fish poisoning is common and occurs in the tropics and temperate regions worldwide.

Clinical Presentation

A person with scombroid poisoning experiences flushing of the face and upper body, severe headaches, palpitations, abdominal cramping, and diarrhea. Severe itching and partial paralysis may also occur. Symptoms occur within 2 minutes to 2 hours after eating the spoiled fish (3). Despite the severe symptoms, the poisoning is usually benign, and the symptoms end within a few hours. A diagnosis of scombroid poisoning is usually based on the onset of signs and symptoms soon after the person has eaten a fish known to be associated with scombroid poisoning.

Prevention

Fish contaminated with histamine may taste extra sharp, although many of these fish do not have an abnormal odor or taste. Handling fish properly and immediately refrigerating fish after it is caught will prevent illness. Cooking fish does not prevent scombroid poisoning.

Treatment

Treating the symptoms, including the use of antihistamines, can reduce the symptoms.

Shellfish Poisoning

Description

Shellfish poisonings occur after a person eat mollusks or crustaceans, such as oysters, clams, cockles, scallops, mussels, crabs, and lobsters that contain toxins. This kind of poisoning is rare and is named after the unique symptoms the toxins produce: paralytic, neurotoxic, diarrheic, or amnesic. Several small marine organisms called dinoflagellates or diatoms produce the toxin responsible for these poisonings. Shellfish either eat or filter these marine organisms and concentrate the toxin in their bodies. People experience the paralytic, neurotoxic, diarrheic, or amnesic symptoms when they eat shellfish that contains the toxin.

Occurrence

Contaminated shellfish are usually found along the coasts of countries with temperate and tropical marine waters, typically during or shortly after algal blooms (“red tides”), which are associated with warm weather.

Clinical Presentation

Eating shellfish that contains marine toxin causes a variety of symptoms within a few minutes to a few hours. In paralytic shellfish poisoning, symptoms appear within 10 to 120 minutes after a person eats contaminated shellfish. The symptoms begin with a tingling or numbness of the face, arms, and legs, followed by headache, dizziness, nausea, and loss of muscle coordination. In most cases of shellfish poisoning, the symptoms are mild and last a few days. In cases of severe poisoning, however, paralysis and respiratory failure occur, and death may follow within 2 to 25 hours (4).

Symptoms of neurotoxic shellfish poisoning occur within a few minutes to a few hours after a person eats contaminated shellfish, but they do not last long. Symptoms include numbness; tingling in the mouth, arms and legs; loss of coordination; upset stomach; and severe muscle aches. No fatalities from neurotoxic shellfish poisoning have ever been reported, and patients usually recover in 2 to 3 days.

Onset of symptoms from diarrheic shellfish poisoning usually occurs within 30 minutes to 3 hours after a person eats contaminated shellfish. The symptoms include nausea, vomiting, and diarrhea, which resolve within 2 to 3 days. This illness is usually not fatal, and patients recover with no long-term effects.

Symptoms of amnesic shellfish poisoning occur within 24 hours after a person eats contaminated shellfish and include nausea, vomiting, diarrhea, headache, disorientation, and possibly permanent short-term memory loss. In cases of severe poisoning, seizures, paralysis, and death may occur. Persons most susceptible to this type of shellfish poisoning are the elderly and those with kidney problems.

Prevention

The only method of preventing shellfish poisoning is to avoid eating mollusks that are locally harvested from areas known to be experiencing red tides. Marine shellfish toxins cannot be destroyed by cooking or freezing.

Because red tides can occur throughout the world, Americans who travel outside the United States should be aware of local conditions before eating shellfish.

Treatment

Treatment for all shellfish poisons is supportive and is tailored to symptoms.

References

1. US Food and Drug Administration, Center for Food Safety and Applied Nutrition. [Homepage on the Internet, updated 2005 Dec 5; cited 2006 June 13]. Foodborne pathogenic microorganisms and natural toxins handbook. Ciguatera. Available from: URL: http://vm.cfsan.fda.gov/~mow/chap36.html.
2. Centers for Disease Control and Prevention. Ciguatera fish poisoning—Texas, 1997. MMWR Morbid Mortal Wkly Rep. 1998;47:692-4.
3. Centers for Disease Control and Prevention, Division of Bacterial and Mycotic Diseases. Marine toxins. [Homepage on the Internet, updated 2005 Oct 12; cited 2006 June 13]. Available from: URL: http://www.cdc.gov/ncidod/dbmd/diseaseinfo/marinetoxins_g.htm.
4. Hui YH, Kitts D, Stanfield PS, eds. Foodborne disease handbook, Volume 4: Seafood and environmental toxins. 2nd ed. New York: Marcel Dekker; 2001.

ALDEN HENDERSON