Tox in The Land: Paralytic Shellfish Poisoning

What is Paralytic Shellfish Poisoning?

  • Most common and most severe form of shellfish poisoning

  • Globally, there are 2,000 cases reported per year

  • Ingestion of shellfish contaminated with saxitoxins and other “paralytic shellfish poisons”

    • Saxitoxins - neurotoxins formed by dinoflagellates of Alexandrium genus

  • PSPs are 1,000 times more potent than cyanide (used in some WWII suicide pills)



How Do You Get Exposed?

  • Certain shellfish:

    • Bivalve mollusks

      • Highest risk with salt-water bivalve mollusks (mussels, clams)

    • Gastropod mollusks

    • Crustaceans

    • Pufferfish

    • Zooplanktivorous fish

  • Certain places/events:

    • Algal blooms (red tides)

    • Temperate climates

      • Can also be in tropical waters

    • In the United States:

      • Seafood in Northeast, Pacific Northwest, Alaskan waters

    • Non-commercial shellfish (esp. Alaska)

  • NOTE:

    • Toxin cannot be destroyed by heat, marinating, or freezing

    • Contaminated seafood smells, tastes, and appears normal

Pathophysiology

  • Saxitoxins from dinoflagellates → taken up by shellfish vectors (do not become ill) → eaten by humans → block voltage-gated Na ion channels → blocks propagation of action potentials in nerve axons and skeletal muscle fibers

Symptoms

  • Neurologic symptoms - can be mild or severe

    • Perioral tingling

    • Ataxia

    • Difficulty swallowing

    • Dizziness

    • Paresthesias

    • Weakness

    • Paralysis

    • Brainstem dysfunction

    • Respiratory failure

    • Other symptoms: diarrhea, vomiting, headache, nausea

 

Timeline

  • Onset: a few minutes to ~4 hours

  • Symptoms tend to improve gradually after 12 hours

  • Resolve completely within a few days

  • Death may occur within 2-12 hours of ingestion

Making the Diagnosis

  • Working dx: Hx of consumption → onset of neurologic symptoms

    • Often can identify a cluster of cases with ingestion of noncommercial harvest

  • Confirmed dx: saxitoxin detected in urine (or samples of seafood)

    • Contact health department to assist with lab confirmation

  • Side note: ruling out others on differential: Tetrodotoxin pufferfish poisoning, Botulism, Ciguatera fish poisoning

Management

  • Treatment is primarily supportive

    • May need to mechanically ventilate if severe

  • Mortality: fatality rate as high as 12% in untreated patients

    • Can be particularly high in children

  • Prevention with health authority monitoring of shellfish beds and notification of public with identifying contaminated shellfish

In Today’s News

  • In May/June 2024, US FDA identified and issued an advisory about elevated levels of saxitoxins in shellfish in Oregon and Washington state

    • Were distributed to restaurants/retailers in several states in USA

    • At least 31 people sick in Oregon

  • Outbreak was attributed to an algal bloom along the coast

  • Such high levels of the toxin have not been detected in Oregon in decades.

AUTHORED BY: JANINE CORLEY, MS4

FACULTY EDITING BY: LAUREN PORTER, DO

ToxLauren McCaffertyTOX, toxicology, toxicity, shellfish, poisoning