Vernon E. Ansdell

Description

• Seafood poisoning from marine toxins is an underrecognized hazard for travelers, particularly in the tropics and subtropics. Furthermore, the risk is increasing as a result of multiple factors such as global warming, coral reef damage, and spread of toxic algal blooms.
• Ciguatera fish poisoning and shellfish poisoning are caused by potent toxins that originate in small marine organisms (dinoflagellates and diatoms).
• Scombroid poisoning is caused by eating improperly chilled fish that contains large quantities of histamine.

Ciguatera Fish Poisoning

Ciguatera fish poisoning occurs after eating reef fish contaminated with toxins such as ciguatoxin or maitotoxin. These potent toxins originate from small marine organisms (dinoflagellates) that grow on and around coral reefs. Dinoflagellates are ingested by herbivorous fish, and the toxins are concentrated as they pass up the food chain to large (usually >6 pounds) carnivorous fish and finally to humans. Toxin in fish is concentrated in the liver, intestinal tract, roe, and head.

Gambierdiscus toxicus, which produces ciguatoxin, tends to proliferate on dead coral reefs. The risk of ciguatera is likely to increase as more coral reefs die as a result of factors such as global warming, construction, and nutrient runoff.

Risk for Travelers

• Over 50,000 cases of ciguatera poisoning occur every year.
• The incidence in travelers to endemic areas has been estimated as high as 3/100.
• Ciguatera is widespread in tropical and subtropical waters, usually between the latitudes of 35 degrees north and 35 degrees south; it is particularly common in the Pacific and Indian Oceans and the Caribbean Sea.
• Fish that are most likely to cause ciguatera poisoning are carnivorous reef fish, including barracuda, grouper, moray eel, amberjack, sea bass, or sturgeon. Omnivorous and herbivorous fish such as parrot fish, surgeon fish, and red snapper can also be a risk.

Clinical Presentation

• Typical ciguatera poisoning results in a gastrointestinal illness, followed by neurologic symptoms and, very rarely, cardiovascular collapse.
• The first symptoms usually appear 1–3 hours after eating contaminated fish and include nausea, vomiting, diarrhea, and abdominal pain.
• Neurologic symptoms appear 3–72 hours after the meal and include paresthesias, pain in the teeth or the sensation that the teeth are loose, itching, metallic taste, blurred vision, or even transient blindness. Temperature reversal (hot objects feel cold and cold objects feel hot) is very characteristic. Neurologic symptoms usually last a few days to several weeks.
• Chronic neuropsychiatric symptoms resembling chronic fatigue syndrome may be very disabling, last several months, and include malaise, depression, headaches, myalgias, and fatigue. Cardiac manifestations include bradycardia, other arrythmias, and hypotension.
• Overall mortality from ciguatera poisoning is about 0.1% but varies due to the toxin dose absorbed and availability of adequate medical care to deal with serious complications such as cardiovascular collapse or respiratory failure.
• The diagnosis of ciguatera poisoning is based on the clinical signs and symptoms and a history of eating fish that are known to carry ciguatera toxin. Commercial kits are available to test for ciguatera in fish, but there is no test for ciguatera in humans.

Preventive Measures for Travelers

• Avoid or limit consumption of the reef fish listed above, particularly when the individual fish weighs 6 pounds or more.
• Never eat high-risk fish such as barracuda or moray eel.
• Avoid the parts of the fish that concentrate ciguatera toxin, such as liver, intestines, roe, and head.
• Remember that ciguatera toxins do not affect the texture, taste or smell of fish, and they are not destroyed by gastric acid, cooking, smoking, freezing, canning, salting, or pickling.
• Commercial kits (if available) can be used to check if the fish is safe to eat.

Treatment

• There is no specific antidote for ciguatoxin or maitotoxin.
• Treatment is generally symptomatic and supportive.
• Intravenous mannitol has been reported to reduce the severity and duration of neurologic symptoms, particularly if given early.

Scombroid

Scombroid, one of the commonest fish poisonings, occurs worldwide in both temperate and tropical waters. The illness occurs after eating improperly refrigerated or preserved fish containing high levels of histamine and often resembles a moderate to severe IgE-mediated allergic reaction.

Fish that cause scombroid have naturally high levels of histidine in the flesh and include tuna, mackerel, mahimahi (dolphin fish), sardine, anchovy, herring, bluefish, amberjack, and marlin. Histidine is converted to histamine by bacterial overgrowth in fish that has been improperly stored (over 20° C) after capture. Histamine and other scombrotoxins are resistant to cooking, smoking, canning, or freezing.

Scombroid fish poisoning occurs worldwide in both temperate and tropical waters.

Clinical Presentation

• Symptoms of scombroid poisoning resemble an acute allergic reaction and usually appear 10–60 minutes after eating contaminated fish. They include flushing of the face and upper body (resembling sunburn), severe headache, palpitations, itching, blurred vision, abdominal cramps, and diarrhea.
• Untreated, symptoms usually resolve within 12 hours. Rarely, there may be respiratory compromise, malignant arrythmias, and hypotension requiring hospitalization.
• Diagnosis is usually clinical. A clustering of cases helps to exclude the possibility of fish allergy.

Preventive Measures for Travelers

• Fish contaminated with histamine may have a peppery, sharp, salty, or bubbly taste, but may also look, smell, and taste normal.
• The key to prevention is to make sure that the fish is promptly chilled (below 15° C–20° C) after capture.
• Cooking, smoking, canning, or freezing will not destroy histamine in contaminated fish.

Treatment

• Scombroid poisoning usually responds well to H1 antihistamines.
• H2 antihistamines may also be of benefit.

Shellfish Poisoning

There are several forms of shellfish poisoning. All occur after ingesting filter-feeding bivalve mollusks, such as mussels, oysters, clams, scallops, and cockles containing potent toxins. The toxins originate in small marine organisms (dinoflagellates or diatoms) that are ingested and concentrated by shellfish.

Risk for Travelers

Contaminated shellfish may be found in temperate and tropical waters, typically during or after dinoflagellate blooms or “red tides.”

Clinical Presentation

Poisoning results in gastrointestinal and neurologic illness of varying severity. Symptoms typically appear 30–60 minutes after ingesting toxic shellfish but can be delayed for several hours. Diagnosis is usually made clinically together with a history of recent shellfish ingestion.

Paralytic Shellfish Poisoning

This is the most common and most severe form of shellfish poisoning. Symptoms usually appear 30–60 minutes after eating toxic shellfish and include numbness and tingling of the face, lips, tongue, arms, and legs. There may be headache, nausea, vomiting, and diarrhea. Severe cases are associated with ingestion of large doses of toxin and clinical features such as ataxia, dysphagia, mental status changes, flaccid paralysis, and respiratory failure. The case–fatality rate averages 6% and may be particularly high in children.

Neurotoxic Shellfish Poisoning

Usually presents as gastroenteritis accompanied by minor neurologic symptoms, resembling mild ciguatera poisoning or mild paralytic shellfish poisoning. Inhalation of aerosolized toxin in the sea spray associated with a red tide may cause an acute respiratory illness, rhinorrhea, and bronchoconstriction.

Diarrheic Shellfish Poisoning

This produces chills, nausea, vomiting, abdominal cramps, and diarrhea. No fatalities have been reported.

Amnesic Shellfish Poisoning

This is a rare form of shellfish poisoning that produces a gastroenteritis that may be accompanied by headache, confusion, and permanent short-term memory loss. In severe cases, seizures, paralysis, and death may occur.

Preventive Measures for Travelers

• Shellfish poisoning can be prevented by avoiding potentially contaminated bivalve molluscs. This is particularly important in areas during or shortly after “red tides.”
• Travelers to developing countries should avoid eating all shellfish, because they carry a high risk of viral and bacterial infections.
• Marine shellfish toxins cannot be destroyed by cooking or freezing.

Treatment

• Treatment is symptomatic and supportive.
• Severe cases of paralytic shellfish poisoning may require mechanical ventilation.

References

1. Ansdell V. Food-borne illness. In: Keystone JS, Kozarsky PE, Freedman DO, Nothdurft HD, Connor BA, editors. Travel medicine. 2nd ed. Philadelphia: Mosby; 2008. p. 475–84.
2. Isbister GK, Kiernan MC. Neurotoxic marine poisoning. Lancet Neurol. 2005;4(4):219–28.
3. Sobel J, Painter J. Illnesses caused by marine toxins. Clin Infect Dis. 2005;41(9):1290–6.
4. Palafox NA, Jain LG, Pinano AZ, et al. Successful treatment of ciguatera fish poisoning with intravenous mannitol. JAMA. 1988;259(18):2740–2.
5. Schnorf H, Taurarii M, Cundy T. Ciguatera fish poisoning: a double-blind randomized trial of mannitol therapy. Neurology. 2002;58(6):873–80.