These symptoms typically are followed by disturbed balance, lack of muscular coordination, slurred speech and difficulty swallowing. In severe poisonings, complete muscular paralysis and death from asphyxiation can occur. Shellfish for human consumption should only be taken from areas free of sewage or chemical contamination. No commercially harvested shellfish are included in the annual quarantine. All commercial shellfish harvesters in California are certified by the state and subject to strict requirements to ensure that all oysters, clams and mussels entering the marketplace are free of toxins.
Commercial harvesting is stopped immediately if potentially dangerous levels of toxins are found.
PSP is caused by eating bivalve shellfish, especially mussels, which have fed on certain highly toxic marine plankton. It occurs only when populations of a single-celled organism, a dinoflagellate know as Alexandrium catanella, become abundant and concentrated in ocean waters. Alexandrium catanella and other plankton are a major food source for bivalve shellfish, which feed by filtering the tiny organisms from the water. The toxins from Alexandrium accumulate in the flesh and digestive tracts of the shellfish. Cases of PSP are associated only with the consumption of bivalve shellfish.