Shellfish Poisoning (Paralytic, Domoic Acid, or Diarrhetic)

Cause: Ingestion of shellfish with a toxin from the phytoplankton Alexandrium catenella for paralytic shellfish poisoning (PSP), ingestion of shellfish with a toxin from marine diatoms Pseudo-nitzschia for domoic acid shellfish poisoning (DASP), ingestion of shellfish with a toxin from marine dinoflagellates Dinophysis for diarrhetic shellfish poisoning (DSP).

Illness and treatment: PSP symptoms begin minutes or hours after eating contaminated shellfish and may include numbness of the mouth and limbs. Severe PSP progresses rapidly to paralysis and respiratory arrest, and may require mechanical ventilation. For DASP, gastrointestinal symptoms begin within 24 hours of ingestion and may be followed within 48 hours by neurological symptoms including confusion, short-term memory loss, seizures, respiratory secretions, and coma. DSP symptoms begin 30 minutes to 36 hours with severe diarrhea and sometimes vomiting, cramps, and chills. There is no anti-toxin for shellfish poisoning.

Sources: Bivalve mollusks such as clams, oysters, mussels, and geoduck concentrate PSP toxin and DSP toxin. Razor clams, other bivalve mollusks, and Dungeness crab concentrate DASP toxin. There is no person-to-person spread.

Additional risks: PSP is only rarely associated with reddish discoloration of the water, although the term “red tide” is popularly used. These shellfish toxins can be present in dangerous amounts even when the harvest site water looks clean. Freezing or cooking does not destroy the toxins.

Prevention: Before harvesting shellfish check the Marine Biotoxin Hotline (1-800-562-5632) or web site for updates on affected sites and site closures, which may not always have signs posted.

Recent Washington trends: Two clusters of PSP have been reported during the past 10 years (7 reports in 2000 and 5 in 1998). Both clusters were associated with mussels gathered recreationally from south Puget Sound waters. In 2011, a family developed DSP from mussels gathered from Puget Sound.

Purpose of Reporting and Surveillance

  • To identify whether the source of transmission is a major pubic health concern (e.g., a commercial shellfish product or recreational harvest area) and to prevent further transmission from such sources.
  • To identify others who shared the exposure and educate them regarding symptoms of paralytic shellfish poisoning to facilitate rapid diagnosis.
  • When the source is a risk to only a few individuals (e.g., shellfish harvested from an area closed to harvesting), to inform those individuals how they can reduce their risk of future exposure.

Legal Reporting Requirements

  • Health care providers and Health care facilities: Paralytic and Domoic Acid poisoning immediately notifiable to local health jurisdiction. Reporting requested for Diarrhetic shellfish poisoning.
  • Laboratories: no requirements for reporting.
  • Local health jurisdictions: Paralytic and Domoic Acid poisoning are immediately notifiable to the Washington State Department of Health (DOH) Office of Communicable Disease Epidemiology (CDE) (206-418-5500 or 1-877-539-4344). Diarrhetic shellfish poisoning can be reported the next business day.