Jellyfish Envenomation

Jellyfish stings are caused by nematocysts, stinging capsules that discharge on contact and inject venom.

Species groups

• Box jellyfish (Cubozoa): Chironex fleckeri and related species in the Indo-Pacific, and Irukandji species such as Carukia barnesi
• Hydrozoa: Portuguese man o' war (Physalia)
• Scyphozoa: Cyanea, Chrysaora, Pelagia and Rhopilema

Stings number in the millions each year, and most are minor.

The box jellyfish Chironex can kill in 2 to 20 minutes through cardiac arrest, since venom causes cardiotoxicity, vasoconstriction and pulmonary hypertension. Irukandji syndrome follows a minor sting with a delay of 5 to 120 minutes (usually 20 to 40) and produces a catecholamine surge with severe hypertension, pulmonary edema, myocardial depression resembling stress cardiomyopathy, and intracranial hemorrhage in some. The Portuguese man o' war causes intense pain with long linear welts.

Complications: cardiac arrest, pulmonary edema, intracranial hemorrhage, skin necrosis, scarring, pigmentation, and delayed hypersensitivity rashes appearing 1 to 4 weeks after the sting.

• Immediate burning and stinging, with whip-like or ladder-pattern red welts that match tentacle prints, and blisters
• Box jellyfish: severe pain and rapid collapse with cardiorespiratory arrest
• Irukandji syndrome: severe low back and abdominal pain, limb and muscle cramps, sweating, anxiety with a sense of doom, vomiting, hypertension, tachycardia and dyspnea
• Man o' war: intense radiating pain, welts, nausea and sometimes lymphangitis
• Red flags: collapse in the water, chest pain, dyspnea, a systolic blood pressure over 200 mmHg, and sting with delayed severe pain

1. Clinical diagnosis from the sting pattern, the setting and the time course.
2. ECG, troponin, and echocardiography (reduced ejection fraction in Irukandji syndrome).
3. Chest radiograph for pulmonary edema.
4. Blood pressure monitoring, electrolytes, glucose, creatine kinase and blood gases.

Differentials: other marine stings, allergic urticaria, contact dermatitis, anaphylaxis, myocardial infarction.

1. First aid for box jellyfish and Irukandji stings: flood the area with vinegar (4 to 6% acetic acid) for at least 30 seconds to stop further discharge, then remove tentacles with gloved fingers or forceps. Do not rub, and do not use fresh water, alcohol or urine.
2. Other jellyfish, including the man o' war: rinse with seawater and remove tentacles. Vinegar is not advised since it can trigger discharge. Then hot water immersion at 45 degrees Celsius for 20 minutes.
3. Collapse after a box jellyfish sting: immediate cardiopulmonary resuscitation, 100% oxygen and vinegar to the skin.
4. Antivenom for severe Chironex envenomation: 1 ampoule (20,000 units) IV diluted in 100 mL over 5 to 10 minutes, repeated up to 3 ampoules, or 3 ampoules IM if IV access is not possible.
5. Irukandji syndrome:
   • Analgesia with fentanyl 0.5 to 1 microgram/kg IV (adults 25 to 50 micrograms) titrated every 5 minutes, or morphine 0.05 to 0.1 mg/kg IV.
   • Magnesium sulfate 10 mmol (2.5 g) IV bolus then 5 mmol (1.25 g) an hour by infusion for 6 to 12 hours (evidence is limited).
   • Severe hypertension: glyceryl trinitrate 10 to 200 micrograms/min IV or phentolamine 1 to 5 mg IV. Avoid beta blockers, which worsen pulmonary edema.
   • Pulmonary edema and cardiac failure: continuous positive airway pressure, and dobutamine 5 to 20 micrograms/kg/min IV.
   • Ondansetron 4 mg IV for vomiting.
   • Observe for at least 6 hours, with ECG and troponin before discharge.
6. Local care: paracetamol 1 g orally every 6 hours, lidocaine 4% gel, and hydrocortisone 1% cream twice daily for 5 to 7 days for persistent rash and delayed hypersensitivity. Tetanus toxoid 0.5 mL IM if not immunized.
7. Infection: antibiotics only if clinically infected.

Prevention: stinger suits, protective nets and seasonal swimming restrictions, and vinegar stations on affected beaches. Counsel on pigment changes and scarring.