Health Effects

All but one of these disorders (diarrhetic shellfish poisoning) are characterized by similar neurologic symptoms (particularly tingling of the extremities). Some also elicit gastrointestinal (nausea, diarrhea, abdominable pain) and/or cardiovascular (pulse rate and blood pressure changes) symptomology. All biotoxin disorders are characterized by rapid onset—within a few hours. The disorders associated with mulluscan shellfish—paralytic shellfish poisoning, neurotoxic shellfish poisoning, amnesic shellfish poisoning, and diarrhetic shellfish poisoning—all elicit nausea, diarrhea and abdominal pain. All but diarrhetic shellfish poisoning cause tingling in the extremities of consumers.

For paralytic shellfish poisoning, the toxins contain a tetrahydropurine skeleton with around 20 forms of basic, water-soluble saxitoxins identified (25). The saxitoxins act by binding to the sodium channels in nerve cell membranes and blocking nerve transmission. Symptoms occur within 1 hour, initially with a tingling sensation of the lips, gums, tongue, and face. Death occurs as a result of respiratory paralysis, usually within a period of 12 hours.

Symptoms of neurotoxic shellfish poisoning include reverse sensation of hot and cold temperatures, muscular incoordination and pain, and lowered pulse rate. Neurotoxic shellfish poisoning is caused by a family of about six chemically related toxins known as brevetoxins. Symptoms begin within about 3 hours and stop in 2-3 days. No deaths have been reported.

Amnesic shellfish poisoning is due to the potent neurotoxin domoic acid, which causes gastroentiritis and mental confusion (1,26). Diarrhetic shellfish poisoning symptoms occur from 30 minutes to 12 hours following ingestion of shellfish. The symptoms usually disappear within 1-3 days and produce no long-term effects. Diarrhetic shellfish poisoning can be distinguished from paralytic shellfish poisoning by the absence of neurologic symptoms.

The disorders associated with finfish: ciguatera, scombroid poisoning and pufferfish poisoning; all elicit nausea, diarrhea, abdominal pain, and tingling of the extremities (1). Other ciguatera symptoms include reversed sensation of hot and cold temperatures, headache, itching skin, muscle and joint pain, metallic taste, malais, anxiety, chills, convulsions, paralysis, hallucinations, lost equilibrium, changes in pulse rate, dilated eyes, and reduced blood pressure. Onset occurs in 2-12 hours. Severe itching, temperature reversal, and tingling of the extremities are the most distinctive symptoms, which may last many months. Morbidity in the Pacific region averages five per thousand (3).

Scombroid poisoning symptoms include rash, flushing, burning of the mouth and throat, and heart palpitation, in addition to nausea, diarrhea, abdominal pain, and tingling of the extremities. Onset occurs in a few minutes to a few hours and the duration is 4-12 hours (11,14,27).

Pufferfish poison is a potent vasodepressor that selectively blocks the sodium channel in excitable membranes (15). The symptoms of intoxication start with almost immediate tingling sensations (usually within minutes but up to 3 hours). In severe cases, respiratory failure and death occur. Because pufferfish poison is found in the highest concentration in the gonads, liver, and intestine, the fish are most dangerous to eat immediately before and during the reproductive season.

All of the more common biotoxins can be measured by bio-assay, immunologic, or chemical techniques (16,17). It is generally more cost-effective to survey or monitor with relatively nonspecific bioassay methods and confirm with more specific methods. However, specific, rapid, low-cost, field methods are under development and will greatly improve controls of illness in the future. All the common toxins (except scombroid poison) can be detected by mouse bioassay, differing in sample preparation and extraction. Mouse bioassay is the most common regulatory method in use. Ciguatera is also measured by cat, mongoose, various aquatic invertebrates, and guinea pig ileum bioassay techniques. A method of measuring diarrhetic shellfish poison in common use in the Netherlands is the rat fecal consistency assay. The toxins of paralytic, neurotoxic, amnesic, and diarrhetic shellfish poisonings, scombroid poisoning and pufferfish poisoning are measured by relatively sophisticated analytic high-performance liquid chromatography (HPLC) methods. The toxins of ciguatera are not yet measured using HPLC. It is reported that ciguatoxin can be detected using a radioimmunoassay or an enzyme immunoassay.

Scombroid poison is detected by measurement of histamine using guinea pig ileum bioassay, fluorometry, col-orimetry, enzyme isotopic assays, or thin-layer chromatography. Toxic samples contain 100-4,000 mg histamine per 100 g fish. The toxic threshold is affected by levels and types of potentiators and microflora present, spoilage conditions, and fish species.

Immunoassay methods have considerable potential for detecting marine toxins. The sensitivity and specificity of this method would quickly eliminate the negative samples so that only the positive sample will require further testing. A number of immunoassay-based kits are available for okadaic acid (28), saxitoxins (29), cigautoxins, brevetoxins, and diarrhetic shellfish toxins (30).

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