Seafood Safety

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Contaminated Species

It should be assumed that all filter feeding molluscs are capable of accumulating domoic acid. However, the only shellfish implicated in cases of ASP have been mussels (Grey, 1988; Bird and Wright, 1989; Duerden, 1989; Shumway, 1989).

Geographic Area

To date, cases of ASP have only been associated with mussels from Prince Edward Island, Canada. Domoic acid has been found in the digestive gland of some sea scallops in the New England area (J. Hurst, personal communication), although there have been no reported cases of ASP in the U.S.

Symptoms & Treatment

ASP causes both gastrointestinal and neurological symptoms. In the early stages of ASP, the individual usually experiences gastrointestinal symptoms. Severe ASP can cause a facial grimace or chewing motion, short term memory loss, excessive bronchial secretions and difficulty breathing. Death can occur. Autopsies have shown brain lesions (Grey, 1980; Shumway, 1989).

Statistics

The first documented case of ASP occurred in 1987, and to date, has not occurred outside of Canada (Duerden, 1989). The blooms of 1987 and 1988 resulted in approximately 130 illnesses and 2 deaths in Canada (Grey, 1988).

Detection & Prevention

HPLC is primarily used to detect domoic acid (the mouse bioassay can be used as a qualitative test) (Shumway, 1989). A standard level of 20 ppm of domoic acid has been set (Duerden, 1989).

Neurotoxic Shellfish Poisoning

Description
Pytchodiscus brevis (formally, Gymnodinium breve) (Concon, 1988), was first recognized as the causative agent for NSP in the mid 1960's (Gervais, 1985). Blooms of this unarmored or "naked" dinoflagellate are usually associated with fish kills, but can also make shellfish toxic to humans (Yasumoto, 1985; Lutz and Incze, 1979). The blooms generally begin offshore and are transported inshore (Gervais, 1985). P. brevis produces 3 known toxins: brevetoxin B, brevetoxin C and GB-3 (Yasumoto, 1985).

Contaminated Species

Oysters and clams are the only shellfish which have been associated with NSP illness (Hughes, 1979). However, it should be assumed that all filter-feeding molluscs are capable of accumulating neurotoxic shellfish toxins.

Geographic Area


NSP is primarily limited to the Gulf of Mexico along the West Coast of Florida (Concon, 1988). There was however, a red tide which occurred in Onslow Bay, North Carolina in 1987 (Pietrafesa et al., 1987). The North Carolina bloom is believed to have been caused by the transportation of P. brevis cells out of the Gulf of Mexico and north by the Gulf Stream.

Symptoms & Treatment

SP resembles a mild case of ciguatera or PSP. Symptoms begin within 15 minute to 3 hours of consuming contaminated shellfish (Hughes, 1979) and usually include: tingling of the face and spreading to other parts of the body, cold-to-hot sensory reversal, bradycardia, dilation of the pupils, and a feeling of inebriation. Less commonly, victims may experience: prolonged diarrhea, nausea, poor coordination and burning pain of the rectum (Hughes, 1979; Concon, 1988). Complete recovery is expected within 48 hours (Hughes, 1979).

Statistics

Neurotoxic shellfish poisoning is rare and mostly confined to Florida. In 1974 there was 1 case, and in 1975 there were 3 cases reported in Florida (Concon, 1988). No deaths have been reported from NSP in the U.S. (Lutz and Incze, 1979).

Detection & Prevention

The state of Florida monitors harvesting areas for toxic dinoflagellates and areas are closed when cell counts exceed 5000 cells/l. Two weeks after dinoflagellate concentrations drop below 5000 cells/l, mouse bioassays are run on shellfish. The area is reopened to harvesting when levels are below 20 MU/100g (Gervais, 1985; Hunt and Tufts, 1979).

Diarrhetic Shellfish Poisoning

Description

Diarrhetic shellfish poisoning was recognized as a pathogen in Japan within the last decade. Several species of dinoflagellates have been associated with DSP including: Dinophysis fortii (Yasumoto, et al., 1980, as cited in Yasumoto 1985), D. acuminata (Kat, 1983), and possibly, D. acuta (Yasumoto, 1985) and D. norvegica (Kat, 1985; Freudenthal and Jijina, 1985). In some areas, DSP dinoflagellates have co-occurred with PSP dinoflagellates, making monitoring and management of shellfish harvesting areas difficult (Freundenthal and Jijina, 1985).
To date, eight lipid soluble toxins have been isolated which are involved in causing DSP. The acidic toxins are okadaic acid, dinophysistoxin -1 and -3 and the neutral toxins are pectenotoxin -1, -2, -3, -4 and -5 (Yasumoto, 1985). Epidemiological data indicate that as little as 12MU of dinophysistoxin - 1 or okadaic acid is sufficient to cause illness in humans (Yasumoto et al., 1980, as cited in Stamman et al., 1987). Laboratory experiments with mice indicate that both okadaic acid and dinophysistoxin -1 may be potent tumor promoters (Suganuma et al., 1988).

Contaminated Species

Filter-feeding molluscs can accumulate toxins in their hepatopancrease even at dinoflagellate concentrations below that necessary to discolor the water. Mussels (Kat, 1983), oysters, hard clams and soft-shell clams (Freudenthal and Jijina, 1985) have been implicated in cases of DSP. Contaminated scallops have caused cases of DSP in Japan (Yasumoto et al., 1980, as cited in Yasumoto, 1985), but the likelihood of scallops causing illness in this country is greatly reduced since the whole scallops are not typically consumed in the U.S., as they are in Japan.

Geographic Area

DSP is a global health hazard. Outbreaks have been reported in Japan, (Yasumoto, 1985) the Netherlands (Kat, 1983), Chile, Spain, France, Sweden, Thailand and Norway (Yasumoto, 1985). There is circumstantial evidence that cases of DSP have occurred in the U.S. (Freudenthal and Jijina, 1985; Freudenthal and Jijina 1988).

Symptoms & Treatment

As the name implies, the symptoms of diarrhetic shellfish poisoning are gastrointestinal in nature. Symptoms usually begin within 3 to 7 hours (range: 30 minutes - 15 hours) of consuming contaminated shellfish and include: diarrhea, nausea, vomiting, moderate to severe abdominal pain and cramps and chills (Stamman et al., 1987; Freudenthal and Jijina, 1985; Freudenthal and Jijina, 1988).
No known fatalities have occurred and total recovery is expected within 3 days, with or without medical assistance (Yasumoto, 1985).

Statistics

Although DSP has not been definitively documented in the U.S., there have been reports of cases in the Mid Atlantic region which are suggestive of DSP (Freudenthal and Jijina, 1985; Freudenthal and Jijina, 1988). These probable cases are based on symptoms, time of onset, negative results from conventional testing, and correlation with seasonal and spatial distribution of Dinophysis from monitoring data in the harvesting areas.



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