Box Jellyfish (Chironex fleckeri)

The most dangerous jellyfish in Australian waters, found in far northern Australia (northern QLD, NT, northern WA). Most stings are minor, but death can occur with several metres of tentacle contact in adults (just over 1 m in children) — death occurs within 20–30 minutes from cardiovascular collapse, so basic life support takes priority over any other first aid.

Clinical features

• Severe local pain
• Erythematous, wheal-like linear stings following tentacle contact
• Rarely, superficial necrosis
• Severe envenoming: significant hypotension within 20–30 minutes, progressing to cardiac arrest without basic life support

Treatment

• Remove tentacles (by hand or washing with seawater).
• Apply vinegar liberally to the sting site and surrounding skin — this prevents further nematocyst discharge (it does not relieve pain, which needs separate analgesia).
• Ice packs and analgesia (parenteral opioids often required) for pain.
• CPR immediately if cardiovascular collapse occurs — this is the single most critical intervention, more important than antivenom.

Hospital treatment:

• IV analgesia (fentanyl/morphine)
• IV box jellyfish antivenom, considered in cardiovascular collapse not responding to standard advanced life support
• Cardiac monitoring, troponin/ECHO if cardiac injury is suspected

From Marine envenomations, Berling & Isbister, Australian Family Physician 44(1-2), 2015 (reprinted).