Seafood Safety

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Scombroid Toxicity
Description

Scombroid toxicity results from ingesting fish which have been improperly handled or stored. The toxin is believed to consist of histamine, and possibly putrescine and cadaverine which potentiate the toxicity of histamine (Taylor and Sumner, 1986). (Putrescine and cadaverine inhibit the histamine-metabolizing enzymes, diamine oxidase and histamine N-methyl- transferase.) Enzymatic decarboxylation of histidine (found in abundance in the free state in dark-fleshed fish) results in histamine (optimal temperature 20-30C). Putrescine and cadaverine are formed by the decarboxylation of ornithine and lysine respectively (Farn and Sims, 1986; Taylor and Sumner, 1986). The production of histamine can be fairly rapid. In one outbreak, threshold toxin levels were reached after only 3 - 4 hours of storage at room temperature (Kow-Tong and Malison, 1987). Certain bacteria, especially Proteus morganii, are believed to cause histamine formation in fish with scombroid toxicity. Other weak histamine forming bacteria include: Hafnia alvei, Klebsiella sp. Proteus sp. (Arnold and Brown, 1978; Omura et al., 1978; Eitenmiller et al., 1980; Taylor and Sumner, 1986).
Studies on the production of histamine in mackerel (Murray et al., 1982) showed that fish which were allowed to spoil in ice, had histamine levels which rarely exceeded 5mg/100g of fish, even when it became unfit to eat. However, storage at higher temperatures (especially above 10C) resulted in high levels of histamine, and production was shown to be exponential. Therefore, levels of histamine over 5mg/100g of fish indicate that the fish has been unnecessarily exposed to high temperatures. The higher the level of histamine, the more abuse there has been.

Seafood Safety Continued

Contaminated Species

Scombroid toxicity mostly effects fish of the Scomberesocidae and Scombridae families, although toxicity is not limited to these fish families. Between 1978 and 1982, 42% of outbreaks reported to the CDC were associated with non-scombroid fish (CDC, 1982 as cited in Kow-Tong and Malison, 1987). Varieties of fish most often implicated in illness include: mahi mahi (Bryan, 1988; MMWR, 1989; tuna (Murray et al., 1982; MMWR, 1989); bluefish (Bryan, 1988; MMWR, 1898); mackerel (Murray et al., 1982); bonito (Murray et al., 1982) and skipjack (Chen et al., 1988).

Geographic Area

Fish of the temperate and tropical regions have been found to cause scombroid poisoning. Between 1973 and 1986 the states which reported the most cases to of scombroid poisoning to the CDC (in descending order) were: Hawaii, California, New York, Washington and Connecticut (MMWR, 1989).
Symptoms & Treatment
Symptoms of scombroid poisoning can begin 10 minutes to four hours after consuming contaminated fish. The most common symptoms include (Arnold and Brown, 1978; Eitenmiller et al., 1980; Murray et al., 1982; Bryan, 1986; MMWR, 1989): metallic, sharp or peppery taste; nausea, vomiting, abdominal cramps and diarrhea; oral blistering and perioral numbness; facial swelling and flushing; headache, and dizziness; palpitations; hives; rapid and weak pulse; thirst and difficulty in swallowing.
Complete recovery usually occurs within 24 hours. Administration of antihistamines results in immediate improvement of patient condition (Taylor and Sumner, 1986).
The dose of histamine required to cause scombroid poisoning in humans is variable. One experiment in which 100-180mg pure histamine was administered orally resulted in only mild symptoms (headache, nausea, vertigo) (Motil and Scrimshaw, 1979 as cited in Taylor and Sumner, 1986). On the other hand, two cases of scombroid poisoning occurred in New Mexico in 1987 from eating mahi mahi which had a histamine level of only 20 mg/100g fish (MMWR, 1989). The discrepancy between pure histamine resulting in only mild symptoms, while relatively low levels of histamine in fish can result in severe symptoms, may be explained by the presence of potentiators in spoiled fish. Potentiators, such as putrescine and cadaverine, may decrease the dose of histamine required to cause scombroid poisoning in humans (Taylor and Sumner, 1986). Variability in dosage required to cause illness may also be due to increased susceptibility in individuals with allergies, asthma or peptic ulcers (Blackwell et al., 1969 as cited in Rice et al., 1976).

Statistics

Scombroid toxicity is a common illness associated with seafood. Between the years of 1977 and 1981, scombroid toxicity was responsible for 37% of the seafood-borne illnesses in the U.S. (USFDA, 1984). From 1973 to 1986, 178 outbreaks, affecting 1096 individuals, were reported to the CDC (MMWR, 1989). No deaths have been reported in the U.S.
Detection & Prevention

Cooking, freezing and smoking are ineffective in removing the toxin from fish flesh. The best way to avoid scombroid poisoning is by preventing its production. This can be done by icing or refrigerating fish soon after capture and maintaining the cold temperature until cooking.

The USFDA has established hazard action levels for histamine in fish. For canned tuna the action level is 50mg histamine/100g fish (USFDA, 1982), and for fresh and frozen fish the level is 20mg histamine/100g fish (USFDA, personal communication).
The method most commonly used to detect histamine is a fluorometric assay (Arnold and Brown, 1978; Taylor and Sumner, 1986). There are several different fluorometric procedures which are all based on the condensation of histamine with o-phthalaldehyde to yield a fluorophore. Other histamine detection techniques which are less commonly used include: an enzymatic assay, thin layer, paper, gas-liquid or high pressure liquid chromatography, and guinea pig ileum bioassay.

Paralytic Shellfish Poisoning

Description

Filter-feeding molluscs can become poisonous to humans by consuming toxic dinoflagellates. There are many species of toxic phytoplankton which cause paralytic shellfish poisoning. The species which commonly blooms in the New England area when the water is warm (April through October) is Protogonyaulax tamarensis (White, 1988) (= Gonyaulax tamarensis, G. excavata, Alexandrium tamarensis and A. fundyense). Some other dinoflagellate species which cause red tides in other parts of the world include: other species of Gonyaulax, Gymnodinium sp. and Pyrodinium bahamense (White, 1988).

PSP can be caused by a combination of any of 18 toxins, depending on the species of dinoflagellate, geographic area and type of shellfish involved. The primary toxins include the carbamate toxins (saxitoxin, neosaxitoxin and gonyautoxin 1, 2, 3, and 4) and the sulfocarbomoyl toxins (B1, B2, C1, C2, C3, and C4). Decarbamoyl toxins (dc-saxitoxin, dc-neosaxitoxin and dc-gonyautoxin 1, 2, 3, and 4), which are derivatives of carbamate or sulfocarbomoyl toxins, can also be present in shellfish (Sullivan and Wekell, 1987; Sullivan, 1988).



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