What causes shellfish toxins?

Most shellfish are filter-feeders that produce shellfish toxins after ingesting toxic algae, such as dinoflagellates. These toxins will accumulate in the bodies of shellfish, especially in their viscera. Therefore, fan scallops, mussels, clams, oysters. and fan shells, are among the common high-risk shellfish causing shellfish poisoning. Moreover, during red tide, when algae in the sea grow in large scale, the number of toxic algae increases, posing a greater risk of seafood contamination.

Types of bivalve shellfish poisoning

Four main types of shellfish poisoning have been identified:

1.        Paralytic shellfish poisoning (PSP)

PSP is the most common type of shellfish poisoning. Symptoms can appear minutes or hours after ingestion of tainted shellfish and include tingling sensation or numbness around the lips, arms and legs, and gastrointestinal discomfort etc. In severe cases, PSP may result in difficulty in swallowing and respiratory arrest and can be life-threatening.

2.        Diarrheal shellfish poisoning (DSP)

DSP is another common type of shellfish poisoning, and its major symptoms include gastrointestinal discomfort such as diarrhea, nausea, vomiting and cramps. Recovery is generally within a few days. No fatalities from DSP have ever been recorded.

3.        Neurotoxic shellfish poisoning (NSP)

NSP is rare and not a life-threatening type. The symptoms it causes are generally mild and include tingling of facial muscles. Recovery is generally within a few days.

4.        Amnesic shellfish poisoning (ASP)

ASP can be life-threatening. Its major symptoms include vomiting, cramp, diarrhea, headache and loss of short-term memory.

Distribution of shellfish toxins

          The amount of toxin in shellfish depends on the number of toxic algae ingested and the distribution of toxins in shellfish varies among different parts. Toxins are largely concentrated in the viscera and gonads of shellfish, while the adductor muscle accumulates the least amount of toxins.

Does cooking eliminate toxins from shellfish?

          Shellfish toxins are heat stable and cannot be not destroyed via cooking or processing. During the cooking process, toxins may be transferred to the cooking juices. In addition, as the toxins do not release unpleasant smell, we are not able to tell if the shellfish are toxic from their appearance.

Safety tips to the Public:

1.       Purchase shellfish from a reliable source;

2.       Scrub and clean shells before cooking and remove their viscera and gonads;

3.       Discard any cooking juices before consumption;

4.       Maintain a balanced diet and avoid excessive consumption of shellfish.