Amnesic shellfish poisoning

Syndrome of shellfish poisoning
Amnesic shellfish poisoning (ASP) is an illness caused by consumption of shellfish that contain the marine biotoxin called domoic acid. In mammals, including humans, domoic acid acts as a neurotoxin, causing permanent short term memory loss, brain damage, and death in severe cases. 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 birds, marine mammals, and humans by consumption of the contaminated shellfish. 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 nonhuman organisms is frequently referred to as domoic acid poisoning.

In the brain, domoic acid especially damages the hippocampus and amygdaloid nucleus. 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 3 days to develop. These include headache, dizziness, disorientation, vision disturbances, loss of short term memory, motor weakness, seizures, profuse respiratory secretions, hiccups, unstable blood pressure, abnormal heart rhythms, and coma. People poisoned with very high doses of the toxin or displaying risk factors, such as old age and kidney failure, can die. Death has occurred in four of 107 confirmed cases. In a few cases, permanent sequelae included short term memory loss and peripheral polyneuropathy. No antidote for domoic acid is known, so if symptoms fit the description, immediate medical attention is advised. Cooking or freezing affected fish or shellfish tissue does not lessen the toxicity. Domoic acid is a heat resistant and very stable toxin which can damage kidneys at concentrations that are 1/100th of those that cause neurological effects.

ASP was first discovered in humans late in 1987, when a serious outbreak of food poisoning occurred in eastern Canada. 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. 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, only four days after the start of the concerted investigation.

In the TV series Elementary episode "The Red Team" (original air date January 31, 2013), a witness is intentionally poisoned with domoic acid. 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. Director Alfred Hitchcock heard about this invasion while working on his adaptation of the Daphne du Maurier novelette "The Birds" for his feature film The Birds (1963), and asked the Santa Cruz Sentinel for any further news copy as "research for his new thriller."