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What is Amnesic Shellfish Poisoning?

Oysters and other shellfish can contain the toxin that causes amnesic shellfish poisoning.
Cooked scallops, a type of shellfish.
Clams, a type of shellfish.
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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 26 July 2014
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Amnesic Shellfish Poisoning (ASP) is a very rare form of food-borne illness caused by a toxin called domoic acid which is secreted by diatoms in the genus Pseudo-nitzschia. This condition is also sometimes known as Domoic Acid Poisoning (DAP), in a reference to the toxin which causes it. ASP was first observed in 1987, and since then, a handful of cases have been observed around the world; the condition also appears to be on the rise due to growing numbers of harmful algae in the ocean.

This condition is called Amnesic Shellfish Poisoning because memory loss and other neurological symptoms are very common. When someone is afflicted with this condition, he or she typically experiences gastrointestinal distress including vomiting, cramps, and diarrhea within 24 hours. If the patient has ingested enough domoic acid or the body is especially vulnerable, neurological symptoms like headaches, dizziness, impaired coordination, and short-term memory loss will emerge within three days.

In the long term, Amnesic Shellfish Poisoning can cause brain damage, and sometimes even death, in elderly patients or patients with impaired kidney function. Because there is no known antidote to domoic acid, treatment focuses on providing supportive care to the patient to ensure that he or she is comfortable. Supportive care may also include long-term measures like physical therapy to address lingering neurological problems.

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While domoic acid can reach especially high levels in shellfish, because they are filter feeders, it can also be present in other seafood, and sometimes it jumps up the food chain to marine birds, as well. This means that during a period of algal bloom, when harmful diatoms and dinoflagellates can also proliferate, it is generally advisable to avoid all seafood until the area has been certified as safe. If consumers purchase seafood and someone becomes ill, the leftovers should be discarded, because domoic acid cannot be eliminated through freezing or cooking. Because seafood is often shipped great distances, it pays to be alert to recall announcements.

Some researchers have suggested that shorebirds affected by DAP may become crazed; the 1961 invasion of birds in Santa Cruz, California which notably inspired Alfred Hitchcock, for example, might have been caused by DOP. Marine mammals can also be affected by Amnesic Shellfish Poisoning, with rising rates of problems in shorebirds and marine mammals suggesting that the diatoms which produce domoic acid are growing more plentiful. Amnesic Shellfish Poisoning can cause animals and birds to become extremely confused, resulting in strandings, starvation, drowning, and other unusual events.

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Discuss this Article

anon961339
Post 9

@orangey03: Do you mind telling me where this occurred? I'm doing a research project on a rare disease. As you know, amnesic shell fish poisoning is rare, and I am supposed to find where the outbreak occurred and how they resolved the problem, but most places are small businesses so I haven't found any documented places affected by this toxin. If you could please help, that would be absolutely amazing. Thanks.

starrynight
Post 8

@JaneAir - As you said, you can get food poisoning from a lot of different things. Remember when a bunch of people got listeria from a cantaloupe? A cantaloupe! I say just eat what you want. Pay attention to food safety and you should be fine.

Anyway, I think it's unfortunate that there is no treatment for this. I wonder if doctors are working on it? I know it's not all that common, but it sure sounds awful!

JaneAir
Post 7

Man! It seems like there just aren't any safe foods to eat. I always knew that meat could cause some pretty serious food poisoning, but I used to think fish was pretty safe. Then everyone started talking about mercury. And now amnesic shellfish poisoning!

I'm pretty disturbed by the fact that the effects of this kind of shellfish poisoning can be so long lasting! As the article stated, the neurological affects of this type of shellfish poisoning can be long term. Unlike most food poisoning where you just get sick for a few days!

I think I'm going to avoid shellfish from now on.

B707
Post 6

This sounds like a horrible disease if it is contracted by a human. Getting sick to your stomach and vomiting is bad enough, but getting symptoms like memory loss, tingling and weakness and a loss of control of movement and emotions would be devastating.

I would say never collect or fish for marine life to eat, if there is a red tide. Watch for signs or call for a report. If I went on vacation to a more or less isolated resort area in a foreign country, I would be very cautious about eating any seafood.

Clairdelune
Post 5

That's interesting about the Hitchcock movie, The Birds. I guess it's possible that a group of birds being affected by amnesic shellfish poisoning gave Hitchcock the idea to make a movie about birds going wild. Watching that movie gave me the eeriest feeling. When I see a bunch of birds together today, I get the same feeling.

The fact that more bird life along shores are being affected by amnesic shellfish poisoning makes it seem like, for some reason, more of the poison is getting inside shellfish. Could it be that more toxins are entering our waters or is it a natural environmental change?

kylee07drg
Post 4

@seag47 – I also suffered from a different type of seafood poisoning called ciguatera fish poisoning. While it isn't as bad as amnesic shellfish poisoning and paralytic shellfish poisoning, it does present with some of the same symptoms.

I ate black grouper that had been caught during a time of the red tide. I didn't know about the algae bloom, so I didn't realize I was in any danger. I thought that toxic seafood only involved shellfish, so I assumed it was safe to eat regular fish.

Like people with the amnesic poisoning, I experienced nausea and vomiting, and like you did with paralytic poisoning, I felt a tingling in my fingers and toes. However, I had one symptom that is unique to ciguatera fish poisoning. When I touched something hot, it felt cold, and cold things seemed hot.

The vomiting went away in a couple of days, but the screwed up sensation of hot and cold lasted for about a year. I was afraid to cook anything, because if I burned myself, I wouldn't know it!

seag47
Post 3

Amnesic shellfish poisoning sounds terrible! It is probably even worse than paralytic shellfish poisoning, which I suffered from after eating infected sea scallops.

They were delicious but not worth the sickness they caused. I ate at a beachside restaurant while on vacation in the Gulf of Mexico, so of course, I ordered seafood.

Within a couple of hours, I felt a tingling all over. Parts of me started to go numb, but I didn't care too much, because I felt absolutely giddy. I know I must have seemed drunk, because I staggered around and fell down on the bed.

My friend knew I hadn't consumed any alcohol, so she felt of my forehead. She said I was burning up with fever.

Another friend who happened to be there with us knew what had happened, because she had experienced it before. She said the symptoms would go away in about three days.

I found out later that some people go into respiratory arrest with this type of poisoning. I'm glad I made it through alive!

orangey03
Post 2

My friend's grandfather got amnesic shellfish poisoning. I was with them on vacation when it happened, and I went to the hospital with them.

We had just eaten at a really good seafood restaurant. By the time we got back to the hotel, her grandfather looked sickly. He said he didn't feel well, and he retired to his room.

We came to check on him a little later. He had started vomiting a lot, and he had diarrhea at the same time, which made him dehydrate quickly. He said his cramps were unbearable.

At the hospital, they told us they couldn't reverse the condition. They could keep him hydrated until the diarrhea and vomiting ceased, though.

A week later, he started having trouble remembering things that had just been said or done. He couldn't remember to turn off the oven, because he didn't remember turning it on. He had to move in with his family, because he was a danger to himself.

OeKc05
Post 1

I feel sorry for those poor birds! Imagine starving to death because you are in a state of confusion!

Though I love the taste of seafood, I avoid eating it anymore because of things like this. I know that amnesic shellfish poisoning is rare, but it is possible, and I want to avoid that possibility.

There are other types of diseases you can get from eating things like oysters and shrimp, and to me, the risk is just too great. If I eat in a restaurant, I have no way of knowing whether or not they got their seafood from an area with an algae bloom, so I just order chicken instead.

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