About Amnesic Shellfish Poisoning

Amnesic shellfish poisoning, also known as ASP, is a rare disease caused by demoic acid that is usually found in razor clams, mussels and dungeness crab but it can be found in other shellfish as well. It is caused by a reddish brown plant that is found in saltwater. On the plant is a diatom called Nitzchia pungens. The toxins from this plant contaminate the shellfish in high doses, and when consumed by humans it can cause serious problems.

ASP was first discovered in 1987. Four people died in Canada after eating shellfish and many others got sick, some of which developed forms of amnesia. In the early 1990’s pelicans on California’s coast near Monterey became crazed and when tested were found to have large amounts of demoic acid in their system. ASP is one of four shellfish syndromes. The other three are Paralytic, Neurologic and Diarrheal.

What Are Diatoms and Domoic Acid?

Diatoms are unicellular organisms that are often found attached to filamentous algae. There are two major groups of diatoms, pennates and centric. Pennates are pen shaped diatoms and centric diatoms are cylinder shaped. Pennates are most likely to be found in freshwater, while the centric can usually be found in marine water. They are basically the brown slimy stuff found on rocks, wood, seaweed etc… that shellfish feed off of.

Domoic acid is a neurotoxin that naturally occurs in marine life and is found in diatoms. The condition caused by this disease is also sometimes called domoic acid poisoning or DAP. DAP can affect all mammals. Domoic acid has been found on the East coast, West coast and in the Gulf of Mexico.

Cause, Symptoms and Treatment of ASP

Shellfish eat the diatoms and during the filtering process retain some of the demoic acid. When there are large levels of algae in the water, shellfish secret less of the toxins, therefore making them more toxic. When humans consume the infected shellfish they get sick. This is a very rare disease, but it can cause:

  • Diarrhea
  • Severe abdominal pain
  • Vomiting
  • Nausea
  • Heart palpitations
  • Severe headaches
  • Permanent short-term memory loss
  • Coma
  • Death

Symptoms usually occur within 24 hours of consumption of infected shellfish. There is no antidote for demoic acid. Patients that develop symptoms after eating shellfish should seek medical attention immediately even though there is very little that can be done.

There is no way to tell if the shellfish is infected with demoic acid. There is no taste or odor associated with the contaminated seafood. State departments of health issue warning when unsafe levels of marine toxins have been found. ASP is usually present in late summer and early fall making that the best time to avoid shellfish consumption if there has been a large algae bloom on the coast.