Food Poisoning from Marine Toxins

Seafood poisoning occurs after eating contaminated fish or shellfish containing a toxin made by dinoflagellates. These small marine organisms are found throughout the oceans and especially in and near coral reefs. The toxins accumulate in shellfish or are passed up the food chain as smaller fish are eaten by larger fish. Seafood poisonings are divided into those associated with fish and with shellfish.

Symptoms of seafood poisoning vary with the toxin ingested and may be gastrointestinal, neurologic, or allergic. Marine toxins are tasteless, odorless, and not affected by cooking or any food preparation. The risk of seafood poisoning is increasing as we add more seafood in our 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.

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 intoxication with a toxin made by a dinoflagellate that can be found in some fish. Large fish become contaminated when they eat reef fish that feed on these small organisms.

Occurrence

Ciguatera is the most commonly reported marine seafood toxin poisoning. About 50,000 to 100,000 people per year who live in or visit tropical and subtropical regions develop 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:

  • Amberjack
  • Barracuda
  • Grouper
  • Kahala
  • Parrotfish
  • Sea Bass
  • Snapper
  • Surgeon fish
  • Ulua

Clinical Presentation

Common symptoms include nausea, vomiting, diarrhoea, cramps, excessive sweating, headache, and muscle aches. Sensations of burning or "pins and needles," 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. Rare deaths occur due to hypotension and cardiovascular collapse. Symptoms often occur within 3 hours, but can occur up to a day or more after eating contaminated fish. Neurologic symptoms may begin several days later and continue for months. People who have had a previous ciguatera poisoning develop more severe symptoms with additional exposures.

The diagnosis is based on the clinical signs and symptoms and a history of eating fish known to have ciguatoxin. Laboratory tests have been developed to test for ciguatoxin in fish.

Prevention

Since no country routinely tests for ciguatoxin in locally caught fish, travellers need to be aware of where the problem occurs and which locally caught fish have been associated with the toxin. Ciguatoxins do not affect the taste or smell of the fish, and they are not destroyed by cooking, smoking, or freezing or through any food preparation. Larger fish (>6 lbs) are more likely to have ciguatoxin. Thus, avoiding consumption of very large reef fish is protective, as well as not eating parts of the fish where the toxin is concentrated: the liver, intestines, head, and roe.

Treatment

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 a "fish allergy." The poisoning gets its name from the fish most commonly associated with this condition, the family Scombridae. Yellowfin tuna, mackerel, skipjack, and bonito belong to this group. Some nonscombrid fish (e.g., herring, bluefish, sardine, anchovy, amberjack, black marlin, and mahi-mahi) can also cause scombroid poisoning

Occurrence

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

Clinical Presentation

A person with scromboid poisoning has flushing of the face and upper body, severe headache, palpitations, abdominal cramping, and diarrhoea. Severe itching and partial paralysis may also occur. Symptoms occur within 2 minutes to 2 hours of eating the spoiled fish. This is typically a benign condition and ends in a few hours. The diagnosis is made by the onset of signs and symptoms soon after eating a fish.

Prevention

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

Treatment

Symptomatic treatment, including the use of antihistamines, can reduce the symptoms.

Shellfish Poisoning

Description

Shellfish poisonings occur after eating mollusks or crustaceans, such as oysters, clams, cockles, scallops, mussels, crabs, and lobsters, that contain a toxin. These poisonings are rare and are named after the unique symptom the toxins produce: paralytic, neurotoxic, diarrheic, or amnesic. Several small marine plants called dinoflagellates or diatoms produce the toxins responsible for these poisonings. Shellfish either eat or filter these marine animals and concentrate the toxin in their bodies. Symptoms occur when shellfish containing these toxins are ingested.

Occurrence

Contaminated shellfish are usually found along the coast of countries with temperate and tropical marine waters and typically with or shortly after algal blooms ("red tides"), which are favored by warm weather.

Clinical Presentation

Eating shellfish with marine toxins produces a variety of symptoms in a few minutes to several hours. In paralytic shellfish poisoning, symptoms appear 10 to 120 minutes after eating the contaminated shellfish and are usually mild. They begin with a tingling or numbness of the face, arms, and legs, followed by headache, dizziness, nausea, and loss of muscle coordination. In cases of severe poisoning, paralysis and respiratory failure occur, and death may follow in 2-25 hours.

Symptoms of neurotoxic shellfish poisoning occur within a few minutes to a few hours but do not last long. Symptoms include numbness, tingling in the mouth, arms and legs, loss of coordination, stomach upset, and severe muscle aches. Neurotoxic shellfish poisoning is not known to have ever caused any fatalities, and patients normally recover in 2-3 days.

Onset of diarrheic shellfish poisoning usually occurs 30 minutes to 3 hours after eating and includes symptoms such as nausea, vomiting and diarrhoea, which resolve within 2-3 days. This disease is not generally life threatening, and patients recover with no long-term sequelae.

Symptoms of amnesic shellfish poisoning occur within 24 hours of eating contaminated shellfish and include nausea, vomiting and diarrhoea, headache, disorientation, and possible permanent short-term memory loss. In severe poisoning, seizures, paralysis and death may occur. Persons found to be most susceptible are the elderly and those with kidney problems.

Prevention

Avoidance of eating mollusks locally harvested from areas known to be experiencing red tides is the only method of prevention.

Since these diseases can occur throughout the world, travellers should be aware of local conditions before eating shellfish abroad. Marine shellfish toxins cannot be destroyed by cooking or freezing.

Treatment

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

Bibliography
  • CDC. Ciguatera fish poisoning—Texas, 1997. Morbid Mortal Wkly Rep MMWR. 1998;47:692-4.
  • CDC [homepage on the Internet]. Atlanta: Division of Bacterial and Mycotic Diseases; [updated 2004 Feb 17; cited 2004 Oct 18]. Marine toxins; [about 6 screens]. Available at URL: http://www.cdc.gov/ncidod/dbmd/diseaseinfo/marinetoxins_g.htm.
  • Hui YH, Kitts D, Stanfield PS, editors. Seafood and environmental toxins. Foodborne disease handbook: Volume 4. 2nd ed. New York: Marcel Dekker; 2001.
  • U.S. Food & Drug Administration, Center for Food Safety & Applied Nutrition. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. Ciguatera. http://vm.cfsan.fda.gov/~mow/chap36.html
  • U.S. Food and Drug Administration [homepage on the Internet]. College Park, MD: Center for Food Safety and Applied Nutrition; [updated 2003 Jan 7; cited 2004 Oct 18]. Foodborne pathogenic microorganisms and natural toxins handbook. Ciguatera; [about 3 screens]. Available from: http://vm.cfsan.fda.gov/~mow/chap36.html

- Alden Henderson

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