Seafood Safety
- Avoid types of fish often contaminated with toxins. (Because barracuda has
been frequently associated with ciguatera, Miami City Code prohibits the sale
of barracuda.)
- Avoid eating large fish of the variety that are potentially toxic
(Lawrence, 1980).
- Avoid eating the viscera and roe of all reef fishes especially during the
reproductive season (Craig, 1980).
- Eat a small piece of the fish and wait several hours in order to determine
if any signs of poisoning occur before consuming the whole fish.
- There is some evidence that washing (leaching) the flesh of toxic fish
effectively removes some of the ciguaterins (Deichmann, 1977 as cited in
Kantha, 1987).
- Persons affected once should avoid eating potentially toxic fish for
several months because a second episode might be more severe. Repeated
exposure may cause extreme sensitivity to the toxin resulting in the onset of
symptoms even when fish containing only trace amounts of toxin are consumed
(Lawrence, 1980).
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 20-30°C).
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 10°C) 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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