Shellfish poisoning is caused by toxins that enter the shellfish in the water before harvesting. Poisoning from shellfish less common than shellfish allergies, which can also harm or kill a person. The diseases caused by shellfish toxins are paralytic, neurotoxic, diarrheic, and amnesic in nature. Careful observation of the shellfish environment can help prevent the 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 impair breathing. Particularly at risk are patients who require a respirator for breathing every day. Vomiting may be induced if the patient is not too weak, and symptoms usually subside in six to twelve hours.
Diarrheic shellfish poisoning (DSP) is caused by toxins produced by algae. Like PSP, it is typically found in bivalves. Symptoms begin immediately after ingestion, and include severe diarrhea and abdominal pain. Treatment is supportive, and symptoms subside within one to two days. Death rarely occurs, and if it does, it is due to dehydration.
Neurotoxic shellfish poisoning (NSP) is also found in bivalves. Symptoms occur from one to three hours after ingestion. These symptoms include numbness and tingling of 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 frequently occur. Treatment is supportive. No deaths have been reported due to NSP.
Amnesic shellfish poisoning (ASP) is a very rare disease caused by a toxin found most often in mussels, clams, and dungeness crabs. Symptoms occur about 24 hours after consumption and include abdominal pain, vomiting, diarrhea, headache, heart palpitations, and short-term memory loss. Seizures, coma, and death can occur in cases of severe poisoning. There is no cure, and treatment is strictly to provide comfort to the patient.
The toxins that cause shellfish poisoning have no odor or flavor. They are not destroyed by cleaning, cooking, or freezing. Careful testing of the water near shellfish beds is important to avoid poisoning in humans. Since these toxins are produced by marine plants most frequently in summer and early fall, avoiding shellfish at these times will reduce the risk of ingesting them.
