Hazard identification and characterisation: Paralytic shellfish poisoning toxins block the sodium channels of excitable membranes of the nervous system and associated muscles, inhibiting action potentials and nerve transmission impulses (ANZFA 1999a).
Symptoms of poisoning usually occur within 30 minutes to 2 hours after ingestion of shellfish, depending on the amount of toxin consumed. A mild case can cause a tingling sensation or numbness around lips, gradually spreading to face and neck; prickly sensation in fingertips and toes; and headache, dizziness, nausea, vomiting, and diarrhoea. Extreme cases (high doses) can lead to paralysis of the diaphragm, respiratory failure, choking sensation and death (Hallegraeff 2003). Predominant manifestations include paraesthesia of the mouth and extremities, ataxia, dysphagia and muscle paralysis; gastrointestinal symptoms are less common. The prognosis is favourable for patients who survive beyond 12–18 hours. In unusual cases, because of the weak hypotensive action of the toxin, death may occur from cardiovascular collapse despite respiratory support (FDA 2003).
The extreme potency of the paralytic shellfish poisoning toxins has, in the past, resulted in an unusually high mortality rate. In a study of paralytic shellfish poisoning in Alaska between 1973 and 1992, 54 outbreaks involving 117 ill people were examined. Illness was not associated with the shellfish toxin concentration, method of food preparation, dose, race, sex, or age (Gessner & Middaugh 1995).
In humans 120–180 µg paralytic shellfish poisons can produce moderate symptoms, 400–1060 µg PSP can cause death, but 2000–10 000 µg is more likely to constitute a fatal dose (Hallegraeff 2003).
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