Jellyfish Stings

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By Stuart M. Caplen, M.D.

Jellyfish are free-swimming marine animals found in waters all over the world. They have stinging tentacles used to capture prey, and some species can deliver a painful sting to humans. It is estimated there are approximately 150 million jellyfish stings a year, typically near coastal beaches.[1]

Taxonomy [1]

Jellyfish come from the class Scyphozoa or true jellyfish which includes Cyaneidae and Pelegiidae. Other jellyfish-like members of the Cnidarians phylum have venomous tentacles but taxonomically are not considered true jellyfish. These include Staurozoa or stalked jellyfish, Cubozoa or box jellyfish, Hydrozoa of which the Physalia physalis or Portuguese man-of-war (PMOW) is a member. The PMOW and the Physalia utriculus (Bluebottle) are classified as siphonophores or animals made up of a colony of organisms working together. Both of the Physalia species have gas filled bladders that float above the water.[2] For linguistic simplicity jellyfish and jellyfish-like organisms will be referred to as jellyfish in this article.

From: Cegolon et al.

How Jellyfish Sting and Adverse Effects of Envenomation

Some jellyfish have a jellylike substance surrounding internal structures, others have a gas bladder or an umbrella-shaped bell. The tentacles are of varying size, ranging from a few millimeters to over 40 meters in length depending on the species. One type of cell in the tentacle is called the nematocyst which is a capsule containing a tightly coiled filament immersed in venom. Tentacles can contain thousands of nematocysts. Jellyfish venom discharge is triggered by mechanical stimuli, such as rubbing against a person or fish. These stimuli lead to the uncoiling of the filament, which can penetrate tissue, and cause the nematocyst to discharge venom into or onto whatever has caused the activation. Nematocysts can function even when separated from the jellyfish or if the jellyfish is dead.[1]

The most common adverse effect of jellyfish stings is a skin reaction. The toxin carried in the tentacles can produce linear, urticarial, painful, or erythematous lesions initially. Stings can also be inconspicuous marks with red flaring, goosebumps, wheals, or just sweating at the site.[3] Later on, the injured areas can become vesicular, hemorrhagic, or even necrotic.[4] The tentacles can become adherent to the skin and potentially cause more venom to be released, even if the jellyfish body is no longer attached. The wounds eventually scab over and may leave permanent scars. Delayed eczematous skin reactions have also been observed in victims days to months after exposure.[4]

Conjunctivitis, iritis and corneal ulcerations may occur with ocular stings.[4]

Seabather's eruption is a pruritic dermatitis due to jellyfish larvae that get inside a swimsuit and can cause repeated symptoms if the swimsuit is worn again without proper washing.[4]

Box Jellyfish Linear Lesions

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Stuart M. Caplen, MD, FACEP, MSM

Dr. Caplen is a retired emergency medicine physician and former emergency department medical director, who also has a Master of Science in Management degree, and green belt certification in Lean/Six Sigma.

Editor’s note: When I was twelve years old I remember very clearly the stings of the PMOW. Although I do not remember exactly my treatment. I do remember the lifeguard debating between vinegar and cream. I may have received both! Rich Strongwater, M.D.


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