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'o h duced by bacteria. These groups of toxins cause very similar symptoms (neurologic and/or gastrointestinal) characterized by rapid onset. Four of these groups of toxins are found in molluscan shellfish consumed in the United States: saxitoxins, brevetoxins, domoic acid, and okadaic acids; and four in finfish: ciguatoxin, maitotoxin, scombro-toxin, and tetrodotoxin (3).

OCCURRENCE Shellfish Poisoning

Shellfish toxins fall into three specific groups; paralytic, amnesic, and diarrhetic (20). None of these toxins are produced by shellfish themselves but are obtained from mi-croalgae such as phytoplankton naturally present in the oceans.

Paralytic. Of the molluscan shellfish-associated disorders, three are found in temperate areas and one in semi-tropical. Paralytic shellfish poisoning (saxitoxins) is found in shellfish such as mussels, clams, oysters, and scallops that have fed on the toxic dinoflagellates (21), including several species of the genus Alexandrium, previously Pro-togonylauax catenella and P. tamarensis (4). The toxins produced by these dinoflagellates tend to persist in shellfish for varying periods of time, depending on shellfish species and tissues involved. Paralytic shellfish poisoning is reported from all temperate oceans of the world; P. catenella on the west coast of North America and P. tamarensis on the east coast. In most cases the water temperature must be 5-8°C. The three families of toxins involved (saxitoxins, neosaxitoxins, and gonyautoxins) are all water soluble and heat stable. The first European case was documented in Norway in 1962 (22). Between 1977 and 1981, the United States had 126 cases reported from nine outbreaks.

Amnesic. Amnesic shellfish poisoning (domoic acid) has been reported in blue mussels from Canada and the United States (Maine). The source of the toxin is the marine diatom Pseudonitzschia (formerly Nitzschia) (7,23). In 1987, more than 100 illnesses and three deaths were reported from the Prince Edwards Island area of Canada.

Diarrhetic. Diarrhetic shellfish poisoning (okadaic acid and derivatives) is found in shellfish, especially mussels, that have fed on toxic marine dinoflagellates and then concentrated the lipid soluble toxins in their hepatopancreas. It appears that the edible muscle tissues remain free of toxin. The causative dinoflagellates (Dinophysis fortii and Dinophysis acuminata) are widespread in occurrence (8). Europe (Netherlands, Spain, France, Sweden), Southeast Asia (Japan, Thailand), and South America (Chile) have all reported outbreaks of diarrhetic shellfish poisoning. As many as 1,300 cases were reported in Japan from 1976 to 1982; and during 1981, 5,000 cases were reported in Spain (9,24).

Neurotoxic. Neurotoxic shellfish poisoning (brevetoxins) is found throughout the Gulf of Mexico, the Atlantic coast of the southern United States, and the Carribbean Sea. The causative organism is the dinoflagellate Ptych-odiscus brevis (5). It is most frequently found on the western coast of Florida but has been confirmed from Texas to North Carolina. Eleven people in three episodes were intoxicated in Florida in 1973-1974 (6). Cases continue to be reported. Oysters, clams, and coquina are primary trans-vectors for the toxins to humans.

Ciguatera Poisoning

About 50,000 cases of ciguatera poisoning are reported annually worldwide; more than 2,000 cases in the United States (mostly Hawaii, Puerto Rico, and Florida). The toxins occur throughout the tropical regions of the world (between 35°N and 34°S) in shallow reef areas, mostly around islands (3). The apparent causative organism is the dinoflagellate Gambierdiscus toxicus (10). Fish that cause human illnesses include mostly barracuda, grouper, snapper, and amberjack. Other affected fishes include mackerel and surgeonfish.

Scombroid Poisoning

Many species of time-temperature abused fresh, canned, salted, or dried fish have been associated with scombroid poisoning (11). Scombroid fish include tuna, skipjack, mackerel, bonito, albacore, bluefish, saury, butterfly king-fish, and seerfish. Nonscombroid fish include mahi-mahi, sardines, pilchards, anchovies, herring, black marlin, and kahawai. These fish normally contain high levels of free histidine that is converted to histamine by a variety of bacteria species. Optimum decarboxylation occurs at 20-25°C, pH 2.5-6.5. Chemical potentiators that are also present in flesh, ie, putrescine and cadaverine, enhance the oral toxicity. There were 78 outbreaks of scombroid poisoning reported to the US Centers for Disease Control between 1983 and 1987 (2).

Puffer Poisoning

Tetrodotoxin is found in the flesh of pufferfish (Tetraodon-tidae). Not all species of puffer are equally toxic. The most notoriously toxic species, Fugu rubripes (tiger puffer), is also said to be the tastiest. Toxin concentration, principally in the ovaries and to a lesser extent in the liver and intestines, is highest during the winter months before spawning. Representatives of the tetraodontids are found throughout a broad circumglobal belt extending from latitudes of 47°N to 47°S. Recently, the primary source of the toxin has been determined to be several marine bacteria including Vibrio alginolyticus (12). In Japan, the only major country where pufferfish (fugu) are a delicacy, tetrodotoxin caused an average of 84 deaths a year between 1886 and 1963; having a fatality rate of 59% of all reported intoxications (1).

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