Learning Objective
By the end of this section, students should be able to identify common seafood toxins, their mechanisms of action, characteristic clinical presentations, and appropriate treatments, which are high-yield for USMLE Step 1 toxicology.
Ingested Seafood Toxins
Toxins from seafood can cause illness by histamine release, Na⁺ channel blockade, or Na⁺ channel activation, leading to neurologic, gastrointestinal, and cardiovascular symptoms.
| Toxin | Source | Mechanism of Action | Symptoms / Presentation | Treatment |
|---|---|---|---|---|
| Histamine (Scombroid poisoning) | Spoiled dark-meat fish: tuna, mahi-mahi, mackerel, bonito | Bacterial histidine decarboxylase converts histidine → histamine | Mimics anaphylaxis: oral burning, facial flushing, erythema, urticaria, pruritus; may progress to bronchospasm, angioedema, hypotension | Antihistamines; Albuterol ± epinephrine if bronchospasm |
| Tetrodotoxin | Pufferfish | Binds voltage-gated Na⁺ channels, preventing depolarization | Nausea, diarrhea, paresthesias, weakness, dizziness, loss of reflexes | Supportive care |
| Ciguatoxin | Reef fish: barracuda, snapper, moray eel | Opens Na⁺ channels, causing depolarization | GI: nausea, vomiting, diarrhea; Neuro: perioral numbness, hot-cold sensation reversal; Cardiac: bradycardia, heart block, hypotension | Supportive care |
USMLE Step 1 Pearls
- Scombroid poisoning mimics an allergic reaction; treat with antihistamines.
- Tetrodotoxin → Na⁺ channel blocker → flaccid paralysis; supportive only.
- Ciguatoxin → Na⁺ channel opener → neurologic symptoms like hot-cold reversal; supportive only.
- Neither tetrodotoxin nor ciguatoxin responds to antitoxins.
