Box jellyfish envenomation — DTM&H MCQ

Correct answer: E — Box jellyfish (Chironex fleckeri)

The correct answer is E, Box jellyfish (Chironex fleckeri). This species is found in the calm coastal waters of tropical Queensland and causes the most severe cnidarian envenomation known, characterised by excruciating pain, whip-like linear wheals from tentacle contact, and rapid cardiovascular collapse due to cardiotoxic, haemolytic and dermatonecrotic venom components. The venom acts within minutes on the myocardium and vasculature, and untreated systemic envenoming can cause death within 20 minutes, which fits the described rapid deterioration. Management is vinegar irrigation to inactivate undischarged nematocysts, cardiopulmonary support, and specific CSL box jellyfish antivenom in confirmed severe cases. This clinical picture (severe local pain plus immediate systemic collapse) is the classic teaching vignette for Chironex fleckeri in tropical medicine exams. Why the other options are wrong: A. Portuguese man-of-war (Physalia): causes painful linear stings but these are typically self-limiting with localised urticarial wheals and rarely progress to cardiovascular collapse, as its venom lacks the potent cardiotoxic action of Chironex. D. Blue-ringed octopus: envenomation causes painless or minimally painful bite marks with neurotoxic (tetrodotoxin) descending paralysis and respiratory failure, not linear wheals or cardiovascular collapse. C. Cone snail: delivers a harpoon-like radular tooth sting causing localised pain and neuromuscular paralysis from conotoxins, not the linear whip-like wheal pattern of tentacle contact. B. Irukandji jellyfish: produces Irukandji syndrome with delayed (20 to 30 minutes) onset of severe systemic pain, sweating, and later cardiac dysfunction or pulmonary oedema, but typically minimal or no visible skin marks and no immediate collapse. Key point: Immediate severe pain with linear tentacle wheals and rapid cardiovascular collapse after a tropical Australian sea swim points to Chironex fleckeri, whereas delayed systemic symptoms without marked skin findings suggest Irukandji syndrome.

Reference: LITFL (Life in the Fast Lane) Toxicology Library, Box Jellyfish (Chironex fleckeri): clinical features and management, https://litfl.com/box-jellyfish-chironex-fleckeri/