What are the different types of shellfish poisoning?

Shellfish poisoning is caused by toxins that enter the shellfish in the water before harvest. Shellfish poisoning is less common than shellfish allergies, which can also harm or kill a person. Illnesses caused by shellfish toxins are paralytic, neurotoxic, diarrheal, and amnesic in nature. Careful observation of the shellfish environment can help prevent infected shellfish from being used for human consumption.

Paralytic shellfish poisoning (PSP) is caused by a toxin released by algae and is found in bivalves. Symptoms begin within minutes of consuming the infected shellfish and include headache, dizziness, tingling, nausea, vomiting, and diarrhea. Muscle weakness can make swallowing difficult and can even affect breathing. Particularly at risk are patients who require a ventilator to breathe every day. Vomiting can be induced if the patient is not too weak and symptoms usually subside within six to twelve hours.

Diarrheal shellfish poisoning (DSP) is caused by toxins produced by algae. Like PSP, it is usually found in bivalves. Symptoms begin immediately after ingestion and include severe diarrhea and abdominal pain. Treatment is supportive, and symptoms resolve within a day or two. Death rarely occurs, and if it does, it is due to dehydration.

Neurotoxic shellfish poisoning (NSP) is also found in bivalves. Symptoms occur one to three hours after ingestion. These symptoms include numbness and tingling in the face, mouth, and extremities, reversal of hot and cold sensation where hot substances feel cold and cold substances feel hot, and loss of coordination. Mild to moderate digestive symptoms also occur frequently. Treatment is supportive. No deaths due to NSP have been reported.

Amnesic shellfish poisoning (ASP) is a very rare illness caused by a toxin most commonly found in mussels, clams, and dungeness crabs. Symptoms occur approximately 24 hours after consumption and include abdominal pain, vomiting, diarrhea, headache, heart palpitations, and short-term memory loss. Convulsions, coma, and death can occur in cases of severe poisoning. There is no cure, and treatment is strictly for the comfort of the patient.

The toxins that cause shellfish poisoning are odorless and tasteless. They are not destroyed by cleaning, cooking or freezing. Careful testing of water near shellfish beds is important to prevent shellfish poisoning in humans. Since these toxins are produced by marine plants most often in the summer and early fall, avoiding shellfish at these times will reduce the risk of ingesting them. All forms of shellfish poisoning are rare, due to strict laws governing testing of waters.

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