Cnidaria include the following:
Corals
Sea anemones
Jellyfish (including sea nettles)
Hydroids (eg, Portuguese man-of-war)
Cnidaria are responsible for more envenomations than any other marine animal. However, of the 9000 species, only about 100 are toxic to humans. The multiple, highly developed stinging units (nematocysts) on cnidaria tentacles can penetrate human skin; one tentacle may fire thousands of nematocysts into the skin on contact.
Symptoms and Signs of Cnidaria Stings
Lesions vary with the type of cnidaria. Usually, lesions initially appear as small, linear, papular eruptions that develop rapidly in one or several discontinuous lines, at times surrounded by a raised erythematous zone. Pain is immediate and may be severe; itching is common. The papules may vesiculate and proceed to pustulation, hemorrhage, and desquamation. Systemic manifestations include weakness, nausea, headache, muscle pain and spasms, lacrimation and nasal discharge, increased perspiration, changes in pulse rate, and pleuritic chest pain. Uncommonly, fatal injuries have been inflicted by the Portuguese man-of-war in North American waters and by members of the Cubomedusae order, particularly the box jellyfish (sea wasp, Chironex fleckeri), in Indo-Pacific waters.
Treatment of Cnidaria Stings
Removal of tentacles
Symptomatic treatment
Various rinses to treat pain and deactivate nematocysts, depending on the specific animal
Cnidaria sting treatment includes removal of adherent tentacles with a forceps (preferably) or fingers (double-gloved if possible) and liberal rinsing to remove invisible stinging cells. The type of rinse varies by the stinging organism:
For jellyfish stings sustained in nontropical waters and for coral stings, seawater rinse can be used.
For jellyfish stings sustained in tropical waters, vinegar rinse followed by seawater rinse can be used. Fresh water should not be used because it can activate undischarged nematocysts.
For box jellyfish stings, vinegar inhibits nematocyst firing and is used as the initial rinse if available, followed by seawater rinse. Fresh water should not be used because it can activate undischarged nematocysts.
For Portuguese man-of-war stings, saltwater rinse can be used. Vinegar should not be used because it can activate undischarged nematocysts.
C. fleckeri but not for the stings of North American species.
Photo courtesy of Robert S. Porter, MD.
Tetanus prophylaxis should be given (see table Tetanus Prophylaxis in Routine Wound Management).
Seabather’s eruption
Seabather’s eruption is a stinging, pruritic, maculopapular rash that affects swimmers in some Atlantic locales (eg, Florida, Caribbean, Long Island). It is caused by hypersensitivity to stings from the larvae of the sea anemone (eg, Edwardsiella lineate) or the thimble jellyfish (Linuche unguiculata
