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Seafood
Many marine creatures are always poisonous when ingested, and others are toxic during certain seasons. Whenever you develop an unexplained illness on an island trip, obtain an accurate dietary history. Problems of diagnosis and treatment of a marine toxin may occur anywhere due to air travel and the universal distribution of seafood.
Ciguatera
The most serious marine toxin, Ciguatera is mainly a tropical disorder, but does occur in semitropical and temperate areas when you eat imported fish. Occasionally a traveler will return home with an undiagnosed illness which turns out to be Ciguatera.
Ciguatera-toxic fish are found around the world between latitudes 35 degrees north and 35 degrees south. They are usually reef fish, but are not identifiable as toxic by external appearance. The toxin is heat-stable, and neither cooking nor freezing will remove it.
Clinical Features
Symptoms begin within two and 12 hours.
Generalized non-specific symptoms include:
- mild weakness;
- dull aches;
- cramps; and
- numbness around the mouth, tongue and throat.
Gastrointestinal symptoms include:
- loss of appetite;
- nausea;
- vomiting; and
- diarrhea.
Neurological symptoms include:
- delirium;
- lack of coordination;
- difficulty walking;
- alterations of temperature perception;
- convulsions;
- coma; and
- death.
The main symptoms clear up in one to two days, but residual weakness, alteration of temperature perception and other symptoms may persist for months. The symptoms are similar to neurological decompression illness, making the diagnosis difficult at times. The diagnosis depends on the history of travel and exposure to fish, followed by development of symptoms.
Prevention
Local knowledge is not always reliable, but should be followed if certain species in the area are thought to be toxic. Prudent preventive measures include not eating any of the following:
- viscera (internal organs);
- exceptionally large reef predators and other species implicated in poisoning: barracuda, grouper, snapper, sea bass, surgeonfish, parrotfish, wrasses, jacks and others;
- moray eels.
Treatment
There are limited first aid and definitive treatment measures. If the fish was ingested in the previous few hours, vomiting can be induced to remove any remaining fragments. The victim should be fully conscious if it is necessary to induce vomiting. The severely toxic victim may require respiratory support. Physician care is required as soon as possible.
Scombroid Poisoning
Mackerel-like fish, such as tuna, bonito, albacore and mackerel, may be the source of scombroid poisoning. Occasionally, non-scombroid fish such as dolphin (mahi-mahi), bluefish and marlin may be the source of the toxin.
When these fish are exposed to the sun or room temperature for several hours, a histamine-like substance, which is very toxic, develops. The reaction is not allergic, but a response to the toxic by-products.
Clinical Features
About 30-60 minutes after ingestion, symptoms of nausea, vomiting, diarrhea and abdominal pain appear. Headache, palpitations and a generalized rash with itching and blister formation may follow. Symptoms may become very severe, with cardiovascular shock. Infrequently, death has occurred.
Prevention
Fish should be properly refrigerated and not exposed to sunlight or warm temperatures for long periods. Discard suspect fish.
Treatment
Induce vomiting if the victim is fully conscious, alert and there is a possibility that fish fragments are still present in the stomach. Consult with a physician as quickly as possible.
Parasitism
Raw or lightly pickled marine or freshwater fish of many species are consumed frequently as sushi, sashimi, gefilte or similar dishes. Marine and freshwater fish are hosts for several roundworms and tapeworms which may be transmitted to humans. Sushi may be the source of diphylobothriasis (fish tapeworm) or anisakiasis (Anisakine roundworm). And, any of the lightly pickled fish of many species also may be the source of anisakiasis. The larvae may be present in many commonly marketed fish, including salmon, mackerel, cod, pollock, herring and sole.
You can prevent this form of parasitism by eating only fish which have been thoroughly cooked to 140 degreesF/60 degrees C. Do not eat raw, lightly pickled or undercooked fish.
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