Nematocysts

Background

• Jellyfish; box jellyfish is most deadly
• Most toxic: Australia and other Indo-Pacific waters

Mechanism

Nematocyst stages of discharge

• Physical contact or osmotic gradient causes discharge of nematocysts
• A spring loaded venom delivery system
• Once opened, a nematocyst releases all of its contained venom

Clinical Features

• Isolated stinging
• Severe
  • Respiratory paralysis
  • Cardiovascular collapse
  • Limb paralysis
  • Death

Irukandji syndrome

• Myalgias, back, chest,
• Abdominal pain
• Nausea and vomiting
• Diaphoresis
• Hypertension
• Tachycardia
• Myocardial injury
• Pulmonary edema

Differential Diagnosis

Marine toxins, envenomations, and bites

• Toxins
  • Ciguatera
  • Scombroid
  • Tetrodotoxin (e.g. pufferfish)
  • Shellfish poisoning
    • Amnesic shellfish poisoning
    • Diarrheal shellfish poisoning
    • Neurotoxic shellfish poisoning
    • Paralytic shellfish poisoning
• Stingers
  • Stingray injury
• Venomous fish
  • Cone shell
  • Lionfish
  • Sea urchins
  • Crown-of-Thorns Starfish
  • Stonefish
  • Other: Catfish, zebrafish, scorpion fish
• Nematocysts
  • Coral reef
  • Fire coral
  • Jellyfish (Cnidaria)
    • Box jellyfish
      • Irukandji syndrome
    • Sea wasp
  • Portuguese man-of-war
  • Sea anemones
  • Seabather's eruption
• Phylum porifera (sponges)
• Bites
  • Alligator and crocodile attacks
  • Octopus bite
  • Shark bite
• Infections
  • Vibrio species in saltwater
  • Aeromonas species in freshwater

Evaluation

• Generally a clinical diagnosis

Management

• Remove tentacles and nematocysts
• Hot salt water immersion (inactivates heat labile toxins)
• Consider topical lidocaine
• Consider oral or parenteral analgesia for severe pain
• Acetic Acid may inhibit or trigger nematocyst discharge and thereby increase or decrease pain depending on species (can use fruit juice or other flavored sodas if vinegar not available)
• Symptomatic treatment for Irukandji syndrome
• Antivenom is available for severe box-jellyfish sting

Avoid

• Urine, ethanol, ammonia
• Fresh or tap water (causes nematocyst discharge via the osmotic gradient)

See Also

• Marine toxins and envenomations

References

1. Ward NT, Darracq MA, Tomaszewski C, et al. Evidence based treatment of jellyfish stings in North America and Hawaii. Ann Emerg Med. 2012;60(4):339-414.
2. Cegolon L, Heymann WC, Lange JH, et al. Jellyfish stings and their management: a review. Mar Drugs. 2013;11(2): 523-50