Archive for the ‘Shellfish poisoning’ Category

Toxins #4 – Shellfish Poisoning

December 27, 2006

Shellfish Poisoning

A local guy showed us how to harvest fresh oysters and clams.  For dinner we ate a big old bucket of fresh-from-the-sea raw oysters, and a pile of steamed clams for dinner. What a treat.  But, within a few hours, we all developed nausea and a sort of drunken feeling – a little hard to walk straight and a kind of floating sensation.  I wouldn’t want to take a sobriety test right now. 

Shellfish Poisoning:

There are three forms of shellfish poisoning, Paralytic, Neurotoxic, and Amnesic.

All caused by the consumption of filter feeders that have fed upon dinoflagellets containing different types of saxitoxins.

These poisonings usually occur with a bloom of the algae such as Red Tide – when the water temperatures and nutrients are favorable for rapid multiplication of the algae, and their numbers increase to the point where they color the water red or brown. 

When this occurs, areas of shellfish harvesting should be closed to prevent the consumption of the filter feeders. 

Like ciguatoxin, these saxitoxins are also heat-stable, so cooking will not eliminate the

History is important in the diagnosis, in that they have recently eaten filter feeders; mussels, clams, oysters, scallops, cockles, crabs, or lobsters. 

As these filter feeders feed upon the dinoflagellets and diatoms, they concentrate the various types of saxitoxins in their gut tissues. 

Unfortunately, these tissues are usually consumed with the rest of the filter feeder. 

The exception is the scallop. If the adductor muscle is the only portion of the scallop that is eaten, it is safe because it does not contain the saxitoxins.

These three forms of shellfish poisoning; Paralytic, Neurotoxic, and Amnesic, are caused by three different types of saxitoxin, each from a different type of dinoflagellet or diatom that was consumed by the filter feeder.

Paralytic Shellfish Poisoning:


Onset is 2 – 24 hours.
Paresthesias of the face, arm, legs
Muscular incoordination
“Floating sensation”

Severe Symptoms:

Muscle paralysis
Respiratory failure
Death is rare, but it can occur due to respiratory failure in 2 – 24 hours.
Neurotoxic Shellfish Poisoning:


Onset in 1 – 3 hours.
Paresthesias of the mouth, arms, and legs
Gastrointestinal upset: nausea, vomiting, diarrhea
Can have temperature reversal

Amnesic Shellfish Poisoning:

Biotoxin is from a diatom – Nitzchia pungens


Onset in 2 – 24 hours
GI distress: nausea, vomiting, diarrhea
Permanent short-term memory loss – yes PERMANENT

Severe Symptoms:

Weakness progressing to paralysis

Treatment of all forms of shellfish poisoning:

Supportive care; rest, liquids, and treat the symptoms.
There are no antitoxins available.
Spontaneous recovery in 2 days to months. 
The short-term memory loss can be permanent.

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