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Diarrhetic Shellfish


Diarrhetic (or diarrheal) shellfish poisoning occurs from ingesting shellfish (such as mussels, cockles, scallops, oysters and whelks) that contain toxins. These toxins cause gastroenteritis symptoms, such as watery diarrhea. 

Steamed mussels have been associated with diarrhetic shellfish illnesses in BC.


Shellfish harvested in BC coastal waters can sometimes be contaminated with this toxin. Self-harvesters of shellfish should check to see if the area they are harvesting from is open.

More on shellfish harvesting.

Information for Health Professionals

Shellfish Related Illness Surveillance Follow-up form

Confirmed Case

  • Clinical illness [1] within 12 hours of consuming at risk shellfish [2];
  • Laboratory confirmation through:
    • Detection of lipophilic shellfish toxins (sum of okadaic acid and dinophysis toxins (DTX-1, DTX-2 and DTX-3)) in ingested at risk shellfish
      • In digestive tissues in excess of 1 mg/kg (1 ppm);
      • In edible tissues in excess of 0.16 mg/kg (0.16 ppm).
    • Detection of high levels of dinoflagellates (Dinophysis spp. and Prorocentrum spp.) associated with shellfish poisoning in water from which epidemiologically-linked at risk shellfish [2] were harvested.

Probable Case

  • Clinical illness [1] within 12 hours of consuming at risk shellfish [2].


  1. Clinical illness defined as: acute gastrointestinal symptoms (nausea, vomiting, abdominal discomfort and/or diarrhea) with possible headache or chills. Illness can last up to 3 days.
  2. At risk shellfish include filter feeding molluscan bivalve shellfish: clams, mussels, scallops (only in midgut gland or hepatopancreas), oysters, cockles, and whelks and the hepatopancreas of crab.
  • diarrhea (watery)
  • nausea
  • abdominal cramps
  • vomiting
  • headache
DSP symptom onset is fairly rapid, and begins between 30 minutes to 15 hours after eating contaminated shellfish. Usually the symptoms start in one or two hours. The recovery period is within 3 days. 

Diarrhetic shellfish poisoning is caused from the ingestion of toxin-contaminated bivalve shellfish and crustaceans. Algal blooms of dinoflagellates, usually during the warmer months of June to October, result in toxin accumulation in filter feeders such as bivalves. The most common species affected and associated with diarrhetic shellfish illnesses are mussels, rare illnesses have also been associated with clams and scallops. The toxins produced are lipophilic and accumulate in the digestive glands (hepatopancreas). In the case of scallops, removal of the gland and eating only the adductor muscle or fleshy part renders scallops safe to eat.

Symptoms usually resolve completely within a few hours to 3 days after shellfish ingestion. There are no known complications (or chronic sequelae) from diarrhetic shellfish poisoning.

The detection of toxin in epidemiologically linked food confirms the diagnosis. Shellfish should not exceed established Canadian standards

There is no antidote. In severe cases, oral rehydration is recommended.

In Canada, CFIA has a national biotoxin monitoring program that includes testing for PSP, ASP, and DSP in bivalve molluscan shellfish. Historically in BC, CFIA's DSP testing focused on lots exported to specific international markets. CFIA has recently expanded their DSP program to include monitoring in other harvest locations. 

Health Canada has established limits for DSP-causing toxins (Canadian Standards). When these regulatory limits are exceeded, effected harvest areas are closed to harvesting.


All shellfish in BC must be inspected by federally registered shellfish processing plants before going to commercial market – this is part of the Canadian Shellfish Sanitation Program (CSSP), the federal monitoring and prevention program in Canada. The CSSP classifies harvesting areas and controls the commercial and recreational harvesting and processing of shellfish for the consumer market. The CSSP is run by 3 federal government agencies (1) Environment Canada - responsible to monitor water quality in shellfish areas, (2) Canadian Food Inspection Agency - responsible for monitoring marine toxins in shellfish areas and for registering and inspecting shellfish processing plants, and, (3) Fisheries and Oceans Canada - responsible for opening and closing harvest areas, and prohibiting shellfish harvesting when bacteriological or toxin levels are unsafe.

More on Shellfish Contamination.

SOURCE: Diarrhetic Shellfish ( )
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