Common marine envenomations


Jellyfish stings Jellyfish stings are very common off both warm and cold water coasts and are the most common marine envenomation encountered in medical practice. The organisms float in seawater, with tentacles that dangle beneath a gelatinous bell. The tentacles often break free, and contact with a free tentacle is common. Cells called nematocysts along the tentacles inject venom on contact, usually causing immediate pain and subsequent linear erythematous urticaria-like lesions. Lesions may progress to purpura and even skin necrosis. There is great variation in the severity of symptoms, depending on the species encountered, the severity of the envenomation, and individual factors such as delayed hypersensitivity reaction after repeat exposure.


Most jellyfish stings off the United States coasts are minor, with stinging followed by rash. Envenomation by the Portuguese man-of-war is more painful and can cause systemic symptoms, such as abdominal pain and hypotension, in addition to localized symptoms.



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Treatment of jellyfish stings primarily consists of gently cleaning the area to remove nematocysts while trying to limit further venom injection. This is best accomplished in seawater because fresh water can cause the nematocysts to fire. Gently scraping the involved area with a smooth edge can also remove nematocysts.4

Many treatments have been proposed and used for jellyfish stings, including urine, alcohol, baking soda, ammonia, window cleaners, papain-based meat tenderizers, and others. Evidence is lacking for most of these, and many can actually trigger embedded nematocysts, worsening the envenomation. Acetic acid, or household vinegar, is used for box jellyfish stings (Chironex fleckeri), which occur in waters off Australia and cause significant morbidity and mortality. There is an antivenin for box jellyfish stings in Australia.


Heat has been shown to reduce pain from the stings of some species and is more effective than cold. The venom of many sea animals is heat labile. Treatment, after removal of the retained stinging cells, consists of immersing the affected body part into very warm, but not scalding, water. Tetanus prophylaxis should be updated if needed; appropriate wound care to prevent infection should be provided. Oral antihistamines may be helpful in treating pruritis. In some cases of persistent or recurrent urticaria, an oral steroid taper may be provided.4

The condition known as seabather’s eruption is caused by jellyfish larva and occurs on East Coast and Gulf beaches and in the Caribbean. The larvae get caught under bathing clothes, causing firing of nematocysts and resulting in a pruritic rash in the pattern of the bathing suit. This rash is treated with oral antihistamines, and low to medium potency topical corticosteroids. When severe and persistent, it may require an oral steroid taper.


Envenomation by the Portuguese man-of-war can cause abdominal pain and hypotension, in addition to localized symptoms.