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 and envenomations

• Toxins
  • Scombroid
  • Ciguatera
  • Neurotoxic shellfish poisoning
  • Paralytic shellfish poisoning
  • Tetrodotoxin (e.g. pufferfish)
• Stingers
  • Stingray injury
• Venomous fish (catfish, zebrafish, scorpion fish, stonefish)
  • Lionfish
  • Sea urchins
  • Cone shells
• Nematocysts
  • Jellyfish (Cnidaria)
    • Box jellyfish
  • Portuguese man-of-war
  • Coral reef
  • Fire Corals
  • Sea anemones
  • Sea wasps
• Bites
  • Octopus

Evaluation

• Generally a clinical diagnosis

Management

• Remove tentacles and nematocysts
• Hot 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
• 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

Authors

Ross Donaldson, Michael O'Brien, MD