Hazard identification and characterisation: The causative compound, domoic acid, is an excitatory amino acid acting as a glutamate antagonist on the kainate receptors of the central nervous system (ANZFA 1999a).
A mild case of amnesic shellfish poisoning is characterised by gastrointestinal disorders (nausea, vomiting, diarrhoea, abdominal pain) and neurological problems (confusion, disorientation, memory loss, seizure, coma). The toxicosis is characterised by the onset of gastrointestinal symptoms within 24 hours, followed by neurological symptoms occurring within 48 hours (FDA 2003).
The toxicosis is particularly serious in elderly patients, and includes symptoms reminiscent of Alzheimer’s disease. All fatalities to date have involved elderly patients (FDA 2003). The neurologic effects can persist for years (Benenson 1995). An extreme case is characterised by decreased reaction to deep pain; dizziness, hallucinations, and confusion; short-term memory loss; and seizures (Hallegraeff 2003).
While the general population is susceptible to this form of shellfish poisoning, the elderly are apparently predisposed to the severe neurological effects of the amnesic shellfish poisoning toxin.
A limited number of human mortalities have also been associated with amnesic shellfish poisoning in Canada, with immunodepressed patients being most at risk. Humans affected had consumed mussels containing 300–1200 µg/g of domoic acid (Hallegraeff 2003).
