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,
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).
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).
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.
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).
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
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
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).
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.
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
No known fatalities have occurred and total recovery is expected within 3
days, with or without medical assistance (Yasumoto, 1985).
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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