Marine biotoxins are poisons that are produced by certains types of algae in seawater. Normally their concentrations in seafood are too low to be harmful, but when changes in environmental conditions cause "algae blooms", the shellfish that feed on algae can build up levels high enough to cause illness.

Different types of marine biotoxins cause different illnesses. Paralytic Shellfish Poisoning (PSP) is a neurologic syndrome caused by consuming shellfish contaminated with marine biotoxins called "saxitoxins." High concentrations of these toxins occur in shellfish during algae blooms known as "red tides," but can also occur in the absence of a recognizable algae bloom. Saxitoxin contamination is monitored in Washington state shellfish harvesting areas and in imported shellfish.

Another marine biotoxin illness is diarrhetic shellfish poisoning (DSP). DSP is caused by consuming mollusks (especially mussels) that are contaminated with okadaic acid or other chemically related toxins through the filter-feeding process. Symptoms of DSP include nausea, vomiting, diarrhea, abdominal pain, fever and chills and occur within 12 hours of eating contaminated shellfish. Symptoms resolve within 3 days and there are no long-term sequelae.

Resources for the general public

• Marine biotoxins, Washington State Dept. of Health
• Marine toxin facts, CDC

Resources for health care professionals

• Paralytic Shellfish Poisoning is a reportable condition in King County: See disease reporting requirements
• Marine toxin facts, CDC