Amnesic shellfish poisoning (ASP) is a human illness caused by consumption of the marine biotoxin called domoic acid.^[1] This toxin is produced naturally by marine diatoms belonging to the genus Pseudo-nitzschia and the species Nitzschia navis-varingica. When accumulated in high concentrations by shellfish during filter feeding, domoic acid can then be passed on to humans via consumption of the contaminated shellfish; reviewed by Bates and Trainer (2006) ^[2], Bejarano et al. (2008) ^[3], Trainer et al. (2008) ^[4], Lefebvre and Robertson (2010) ^[5], Bargu et al. (2011) ^[6], Bargu et al. (2012) ^[7], Lelong et al. (2012) ^[8] and Trainer et al. (2012) ^[9].

Although human illness due to domoic acid has only been associated with shellfish, the toxin can bioaccumulate in many marine organisms that consume phytoplankton, such as anchovies, and sardines. Intoxication by domoic acid in non-human organisms is frequently referred to as "domoic acid poisoning" or "DAP". In mammals, including humans, domoic acid acts as a neurotoxin, causing permanent short-term memory loss, brain damage, and death in severe cases.

Symptoms and treatment[link]

In the brain, domoic acid especially damages the hippocampus and amygdaloid nucleus.^[1] 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. See reviews by Ramsdell (2007) ^[10] and Pulido (2008) ^[11].

Gastrointestinal symptoms can appear 24 hours after ingestion of affected molluscs. They may include vomiting, nausea, diarrhea, abdominal cramps and haemorrhagic gastritis. In more severe cases, neurological symptoms can take several hours or up to three days to develop. 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 has occurred in 4 of 107 confirmed cases. In a few cases, permanent sequelae included short-term memory loss and peripheral polyneuropathy.

There is no known antidote available for domoic acid, so if symptoms fit the description, it is advised to go quickly to the hospital. Cooking or freezing affected fish or shellfish tissue does not lessen the toxicity.

Discovery[link]

ASP was first discovered in humans late in 1987, when a serious outbreak of food poisoning occurred in eastern Canada.^[1][12] Three elderly patients died and other victims suffered long-term neurological problems. Because the victims suffered from memory loss, the term "amnesic" shellfish poisoning is used.^[13] 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 poisoning toxins 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 ^[14][15]

Possible animal effects[link]

On June 22, 2006, a California brown pelican, possibly under the influence of domoic acid ^[16], flew through the windshield of a car on the Pacific Coast Highway. The phycotoxin is found in the local coastal waters.

Since March 2007, marine mammal and seabird strandings and deaths off the Southern California coast have increased markedly. These incidents have been linked to the recent and dramatic increase of a naturally occurring toxin produced by algae. Most of the animals found dead tested positive for domoic acid.

According to the Channel Islands Marine and Wildlife Institute (CIMWI) ^[17], "It is generally accepted that the incidence of problems associated with toxic algae is increasing. Possible reasons to explain this increase include natural mechanisms of species dispersal (currents and tides) to a host of human-related phenomena such as nutrient enrichment (agricultural run-off), climate shifts or transport of algae species via ship ballast water."

In popular culture[link]

In the "Bad Fish" episode of Get a Life (original air-date: February 2, 1992), Sharon and Gus get amnesia after eating bad shellfish, and Chris seizes the opportunity to convince them that they are his best friends.

Domoic acid poisoning may have caused an August 18, 1961 invasion of thousands of frantic seabirds in Capitola and Santa Cruz, California^[18]. Director Alfred Hitchcock heard about this invasion while working on his adaptation of Daphne du Maurier novelette "The Birds" for his feature film The Birds (1963), and asked the Santa Cruz Sentinel newspaper for any further news copy as "research for his new thriller".

See also[link]

• Diarrhetic shellfish poisoning (DSP)
• Neurotoxic shellfish poisoning (NSP)
• Paralytic shellfish poisoning (PSP)
• Harmful algal blooms (HABs)

References[link]

External links[link]

• Amnesic Shellfish Poisoning at Woods Hole Oceanographic Institution
• Domoic acid and Pseudo-nitzschia references at Fisheries and Oceans Canada
• Amnesic Shellfish Poisoning, Domoic Acid, and Pseudo-nitzschia links at the ISSHA website
• Domoic acid at International Programme on Chemical Safety
• DOMOIC ACID — A MAJOR CONCERN TO WASHINGTON STATE’S SHELLFISH LOVERS at Washington Department of Fish and Wildlife
• Crisis off our coast at the International Bird Rescue Research Center
• Domoic Acid Poisoning Linked to Recent Marine Strandings and Deaths at Heal the Bay
• Domoic Acid Information and History at the Channel Islands Marine and Wildlife Institute

There are four syndromes called shellfish poisoning, which share some common features and are primarily associated with bivalve molluscs (such as mussels, clams, oysters and scallops). ^[1] These shellfish are filter feeders and, therefore, accumulate toxins produced by microscopic algae, such as dinoflagellates and diatoms, and cyanobacteria.

The syndromes are:

• Amnesic shellfish poisoning (ASP)
• Diarrheal shellfish poisoning (DSP)
• Neurotoxic shellfish poisoning (NSP)
• Paralytic shellfish poisoning (PSP)

See also[link]

• Cyanotoxin
• Foodborne illness

References[link]

1. ^ Silver, Mary Wilcox (2006), "Protecting Ourselves from Shellfish Poisoning", American Scientist 94 (4): pp.316–325 

External links[link]

• Human Illness Associated with Harmful Algae
• More information on shellfish food poisoning