Amnesic shellfish poisoning

Overview
Amnesic shellfish poisoning (ASP) is one of the four recognised syndromes of shellfish poisoning, which are primarily associated with bivalve mollusks (such as mussels, clams, oysters and scallops). These shellfish are filter feeders and, therefore, accumulate toxins produced by microscopic algae in the form of dinoflagellates and diatoms.

ASP results from consumption of domoic acid. In the brain, domoic acid especially damages the hippocampus and amygdaloid nucleus. It damages the neurons by activating AMPA and kainate receptors, causing an influx of calcium. Although calcium flowing into cells is a normal event, the uncontrolled increase of calcium causes the cell to degenerate.

The chemical can bioaccumulate in marine organisms that eat phytoplankton, such as shellfish, anchovies, and sardines. In mammals, including humans, domoic acid acts as a neurotoxin, causing permanent short-term memory loss, brain damage, and death in severe cases. Harmful algal blooms are associated with the phenomenon of ASP. Cooking or freezing affected fish or shellfish tissue does not lessen the toxicity.

Symptoms and treatment
Gastrointestinal symptoms appear within 24 hours of ingestion of molluscs contaminated with domoic acid. They may include vomiting, nausea, diarrhea, abdominal cramps and haemorrhagic gastritis. In more severe cases, neurological symptoms develop after a delay of several hours or up to three days. These include headache, dizziness, disorientation, vision disturbances, loss of short-term memory, motor weakness, seizures, profuse respiratory secretions, hiccoughs, unstable blood pressure, cardiac arrhythmia, and coma.

People poisoned with very high doses of the toxin or displaying risk factors such as old age and renal failure can die. Death occurred in 4 of the 107 confirmed cases. In a few cases, permanent sequelae included short-term memory loss and peripheral polyneuropathy.

There is no antidote available for domoic acid and treatment is symptomatic.

Discovery
ASP was first discovered when, in late 1987, a serious outbreak of food poisoning occurred in eastern Canada. Three elderly patients died and other victims suffered long-term neurological problems. Because of the memory loss problem, the term amnesic shellfish poisoning (ASP) is used to refer to this clinical syndrome [M. A. Quilliam, J. L. C. Wright, Anal. Chem., 61 (1989) 1053A]. The story made front-page newspaper headlines.

Epidemiologists from Health Canada quickly linked the illnesses to restaurant meals of cultured mussels harvested from one area in Prince Edward Island, a place never before affected by toxic algae. Mouse bioassays on aqueous extracts of the suspect mussels caused death with some unusual neurotoxic symptoms very different from those of paralytic shellfish poison and other known toxins. On December 12, 1987, a team of scientists was assembled at the National Research Council of Canada laboratory in Halifax, Nova Scotia. Integrating bioassay-directed fractionation with chemical analysis, the team identi­fied the toxin on the afternoon of December 16, just 4 days after the start of the concerted investigation.

Possible animal impacts
On June 22, 2006, a California brown pelican, possibly under the influence of domoic acid, flew through the windshield of a car on the Pacific Coast Highway. The acid is found in the local seas.

Domoic acid poisoning may also have caused a 1961 invasion of thousands of frantic seabirds in Santa Cruz, California. Director Alfred Hitchcock heard about this invasion while working on his adaptation of Daphne du Maurier novella "The Birds" for his feature film The Birds (1963).