ABSTRACT
In late 1987, 250 individuals with gastrointestinal (GI) distress and central nervous system (CNS) disorders appeared at different clinics in Montreal, Canada. The medical history revealed that these patients had one thing in common. They all consumed steamed blue mussels (Mytilus edulis) at dinner the previous night. The tainted mussels originated from Prince Edward Island (PEI), and had been cultivated in three river estuaries on the east coast of PEI (1). The intoxicated patients exhibited GI disorders, including nausea, vomiting, abdominal cramps, and diarrhea, about 24 h after the consumption of mussels. This was followed by the neurological symptoms of headache, confusion, disorientation, loss of short-term memory, seizures, and coma within 48-72 h (2). Some patients were treated and allowed to go home, whereas other were admitted into hospitals. In fact, some patients were so seriously ill that they required intensive care. Four patients died as a result of amnesic shellfish poisoning. An autopsy of dead patients revealed marked neuronal lesions and loss, which was predominantly localized in the hippocampus and amygdala (3). The toxin in mussels causing poisoning was identified as domoic acid (DA) which is a tricarboxylic amino acid (4). It was later realized that DA toxin was produced by a pennate diatom, Nitzschia pungens (5), which was filtered from water by mussels and accumulated in their stomach (6). The human poisoning associated with cultivated mussels was reported for the first time ever in North America. DA was previously reported to be present in a seaweed, Chondria armata, and its extract was used to expel intestinal worms in young children in Japan (7). It was also the first time DA was ever found in shellfish cultivated in Canadian waters. Equally surprising were the findings that (1) Nitzschia pungens has never been associated with DA production, (2)
nor do we know the circumstances which produced Nitzschia pungens bloom, and (3) the conditions favorable for DA synthesis by the phytoplankton. We also do not know how this diatom migrated to waters in this part of the world.
