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What is Amnesic shellfish poisoning and explain in detail?
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.

Symptoms and treatment
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.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.

Discovery
ASP was first discovered in humans late in 1987, when a serious outbreak of food poisoning occurred in eastern Canada