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Paralytic Shellfish Poisoning (PSP)

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Reporting Obligations

Confirmed and suspected cases shall be reported to local Health Unit.

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Aetiologic Agent

Paralytic Shellfish Poisoning (PSP) is an illness caused by toxins that are produced by oceanic phytoplankton or dinoflagellates. There is an extensive number of PSP-type marine biotoxins worldwide. The toxin most commonly associated with paralytic shellfish poisoning is saxitoxin produced mainly by Alexandrium species and other dinoflagellates. PSP neurotoxins are water-soluble and heat-stable.

Clinical Presentation

PSP is a serious illness that may have potentially fatal effects.

Onset of symptoms typically begins within a few minutes and up to 10 hours after consumption. The intensity and progression of the symptoms are dependent on the type, dose, and concentration of the toxin ingested in the shellfish.

Symptoms of PSP typically begin with a prickly, tingling or numbness sensation (paresthesia) around the lips or mouth, which gradually spreads to the face and neck. Other early symptoms may include prickly, tingling, or numbness in the fingertips/toes; dizziness or a “floating” sensation; headache; diaphoresis (i.e., sweating) or excess saliva production. Gastrointestinal symptoms such as nausea, vomiting and abdominal pain may occur.

In severe cases, paresthesia occurs in the arms and legs, ataxia (i.e., lack of coordination/balance), incoherent speech, dysphagia (e.g., difficulty swallowing), and a rapid pulse may occur.

In extreme cases, rapid progression to respiratory muscle paralysis and respiratory failure may occur. This can lead to respiratory arrest and death. Most deaths occur within 12 hours of ingestion. Typically, symptoms resolve completely within a few hours to a few days. In severe and extreme cases, individuals who survive for 24 to 48 hours usually recover without long-term complications.

Modes of Transmission

Consumption of contaminated shellfish, raw or cooked.

Incubation Period

Less than 12 hours. Symptoms may occur from within a few minutes to up to 12 hours after consumption of shellfish contaminated with toxin.

Period of Communicability

Not communicable by person-to person transmission.

Risk Factors/Susceptibility

Susceptibility varies. Some individuals can tolerate large doses of the toxins. Children are more susceptible. Alcohol consumption may have a protective effect against the toxin by acting as a diuretic.

Diagnosis and Laboratory Testing

A diagnosis of PSP should be based on clinically compatible signs and symptoms, in the context of a history of recent shellfish/seafood consumption. Confirmation of the diagnosis can be made by detection of the biotoxin (i.e., saxitoxin, or its analogues) at concentrations sufficient to cause symptoms in the shellfish remaining from the same lot or harvest area as the shellfish consumed/implicated in the illness.

Detection of PSP toxins in a urine sample, although not currently available in Canada, can be carried out in partner labs if clinically warranted.

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Treatment and Case Management

Treatment is under the direction of the attending health care provider. Individuals should seek immediate medical attention. There is no known anti-toxin for PSP. Treatment is supportive. Individuals with serious illness should be hospitalized and placed under respiratory care. In general, supportive measures are the basis of treatment for PSP, especially ventilator support in severe cases.

Public Health staff will investigate to determine the possible source of the illness and to discuss contacts. Although not transmissible from person to person, contact follow-up is recommended for others who may also have consumed potentially contaminated food. These individuals should be instructed on disease symptoms, when to seek medical attention, transmission, incubation period and preventive measures.

Additional Resources

Canadian Food Inspection Agency. “Marine Toxins in Bivalve Shellfish.”


Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2022.