Cnidaria Envenomation Clinical Presentation

Updated: Mar 16, 2022
  • Author: Spencer Greene, MD, MS, FACEP, FACMT, FAAEM; Chief Editor: Joe Alcock, MD, MS  more...
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Three different mechanisms are responsible for toxicity from Cnidaria envenomations: immediate toxicity, immediate allergic reaction, and delayed allergic response.

When evaluating a patient with a suspected envenomation, it is essential to obtain the following information: (1) time of envenomation; (2) location of the incident; (3) description of the animal; (4) onset, progression, and quality of signs and symptoms; and (5) what treatments have thus far been attempted.

The severity of the envenomation is determined by a variety of factors, including (1) size, age, species, and overall health of the animal; (2) the size, age, and underlying health of the patient; (3) the surface area of the involved skin; and (4) the duration of contact.

Though not applicable to known envenomations, it is always wise to consider envenomation in the differential diagnosis of unexplained drowning and near-drowning.


Physical Examination

Pain and dermatologic abnormalities are the most obvious, and often the only, signs and symptoms of a Cnidarian envenomation. Erythema develops rapidly after envenomation, followed by edema and purple-brown vesicular lesions, often found in a whiplike pattern. Most lesions last for minutes to hours, but some may hemorrhage or progress to full-thickness necrosis over the next 1-2 weeks.

Seabather's eruption, or "sea lice", is characterized by small, intensely pruritic urticarial lesions confined to covered areas of the body. It develops when the larvae of several species of thimble jellyfish become trapped and maintain prolonged contact with the victim's skin. The lesions may last for up to 2 weeks but have no permanent consequences

Ocular abnormalities such as conjunctivitis, chemosis, corneal ulcerations, and lid edema have been observed following envenomations.

Findings indicative of systemic envenoming include pulmonary edema, variable blood pressure, tachycardia, weakness, headache, nausea, vomiting, muscle spasm, fever, pallor, syncope, respiratory distress, paresthesias, acute renal failure, hemolysis, myocardial infarction, and cardiopulmonary arrest. [18, 19] These are most likely to occur following envenomation from C. fleckeri or P. physalis. Oftentimes, the local findings are minimal.

Uncommon complications following Cnidaria envenomation include Guillain-Barre syndrome, [20] mononeuropathy, [21] and takotsubo cardiomyopathy. [22]