Last updated 28, March 2013
The term “jellyfish” describes an enormous number of marine animals belonging to the phylum Cnidaria. The phylum includes hydroids, medusae, anemones, polyps and corals, all capable of inflicting a varied array of stings and injuries.
Cnidarians contain cnidocytes, a specialized cell capable of injecting venom through microscopic barbs. Stings occur when the victim comes into direct contact with the creature’s tentacles or appendages, which may carry millions of these microscopic stinging cells. The animal and its tentacles are typically quite friable, and broken-off tentacle fragments in the surf or washed up on the beach can retain their toxicity and stinging capacity even if they appear dried out and withered.
The severity of these stings can range from a painless almost imperceptive numbness, to burning skin reactions with mild to moderate blistering. Severe life-threatening reactions are characterized by excruciating pain, nausea, vomiting, shortness of breath, muscle spasms, low blood pressure, dysrhythmias and cardiovascular failure.
While most species pose little threat, some envenomations are quite serious and potentially life-threatening. The essential factors that influence symptom severity include venom potency, victim size, and the extent of body surface area in direct contact with stinging cells.
Box Jellyfish (Cubozoans)
Box jellyfish belong to the Class Cubozoa (cube-shaped medusae), a large subgroup of Cnidarians. Though not all cubozoans are dangerous to humans, some species like Chironex fleckeri (aka Sea Wasp), Chironex yamaguchii, Chiropsalmus quadrigatus and Chiropsalmus quadrumanus (aka. the Four-handed jellyfish) are considered among the most venomous of all creatures on earth and are responsible for more human fatalities than any other marine organism. According to health authorities in Queensland, Australia, where the highest number of cases are recorded, box jellyfish have been responsible for at least 64 well-documented deaths in Australian waters since 18835. Rapid toxin absorption impacts the cardiovascular system and can lead to death from cardiac arrest in as little as three minutes — scarcely enough time for rescue response. The mechanism of action apparently involves massive potassium release from red blood cells leading to deadly dysrhythmias and cardiovascular collapse. Some recent studies involving zinc gluconate seem to be promising, but so far prevention is the key measure when visiting the Indo-Pacific seas, the endemic region for the vast majority of venomous species6.
Portuguese Man-of-War(Physalia spp.)
While the species of Physalia are commonly considered jellyfish, these free floating cnidarians are not true jellyfish. These cnidarians are more closely related to hydroids and fire coral than to the Box jellyfish and other common medusae. A single specimen of Portuguese Man-of-War (PMOW) is not actually a single animal but a colony that consists of at least four different polyps. One of these polyps, the marissa or sail (a gas-filled bladder meant to catch wind currents), gives them their peculiar and unmistakable appearance. The gas bladder, known as pnematophore, is filled with atmospheric gases, and may contain up to 90 percent carbon dioxide (CO2). There are two species for this genus: the larger Atlantic(Physalia physalis;aka Portuguese Man-of-War) and its smaller IndoPacific relative (Physalia utriculus;aka Bluebottle). The Atlantic species is found from south Brazil through the Gulf of Mexico and all along the eastern United States, with sightings as far north as Nova Scotia. Further east, they are found around South Africa and as far north as the Mediterranean and Scotland. While the Pacific specie is typically found in Australia, the Indian Ocean and New Zealand, they have also been reported in the Hawaiian Islands.
Because of their propensity to cause systemic symptoms, Cubozoans and Physalia species are considered among the most dangerous cnidarians.
The use of lightweight dive skins provides adequate mechanical protection against jellyfish stings.
NOTE: Jellyfish stings may trigger severe allergic reactions. First aid providers should remain watchful and prepared to treat severe allergic reactions if they occur.
NOTE: Nematocysts are mechanically activated. For this reason, medical texts and first aid manuals often recommend against rubbing or manipulation of the stung area as this may stimulate additional nematocyst firings. Despite the truth underlying this common advice, those conscious and able, will likely rub the stung site vigorously and almost reflexively before first aid is deployed. This simple action may be useful in the moment, as it can result in tentacle removal. Once out of the water, first aid can be initiated.
First-aid treatment remains the same for all organisms, although some species may require additional interventions. Be aware that first aid treatment protocols may vary somewhat in different parts of the world. (See below regarding Portuguese man-of-war). The following describes a general first-aid approach for all cnidarian species:
Inactivation. Irrigate the area with generous amounts of household vinegar (4 to 6 percent acetic acid solution). This does not reverse the effects of venom or control pain, but may help to prevent further discharge of unfired nematocysts.
Removal. Visible tentacles or filaments should be carefully removed with the aid of fine tweezers or protective barriers. Gloves, dive skins, women’s stockings or other thin material can provide enough protection to prevent envenomation of rescuers during tentacle removal. Though not recommended, the highly keratinized surface of the hands and fingers is generally thick enough to prevent venom absorption. If tentacles or filaments are handled, the rescuer’s hand (and any barrier material used) must be assumed to contain unfired nematocysts. To avoid inadvertent contact, exposed surfaces, skin and barrier materials should be treated with vinegar and hot water before touching anything or anybody else.
Washout. After liberal use of household white vinegar and removal of any visible tentacles, filaments or debris, wash the area with seawater or saline solution. Avoid rubbing and avoid the use of fresh water as these can stimulate nematocyst discharge.
Symptomatic treatment. Treatment usually consists of painkillers, anti-inflammatory medications and topical anesthetics.
Temperature. May help reduce pain. Immerse the affected area in hot water (113 °F / 45 °C) for 30 to 90 minutes (repeat as necessary). Local application of cold (if a hot water or hot pack are not available) can also provide pain reduction. Reports indicate that the application of heat may provide more effective pain relief than the use of cold, but cold packs should not be refused or avoided on this basis.
Test the water yourself prior to exposing it to the injured person. Envenomations may alter pain tolerance and in some cases may enable exposure to water hot enough to scald.
Heat vs. Thermolysis
The application of (or cold) can be an effective way to reduce pain associated with marine life envenomations and other injuries.
Thermolysis(thermo: heat,lysis: to break down)
Thermolysis refers to the application of high heat (113F/45C) as a way to break down proteinaceous (protein containing) toxins in an attempt to reduce their impact. Though this may sound like a desirable technique, it has some downsides that worth considering. Of primary imporimportance is the fact that heat will not discriminate between the proteins in toxins and those in normal tissue. As such, thermolysis carries a high risk of causing thermal burns. In addition to tissue injury, there are two additional factors that impact the potential effectiveness of this technique.
Use of topical steroids and antihistamines may be useful to reduce local swelling and possible allergic reactions.
NOTE: Regarding First Aid for Portuguese Man-of-War The American Heart Association (AHA) recommends vinegar as an effective measure to prevent unfired nematocysts from discharging for all cnidarian species2. However, in the case of Physalia utriculus (Bluebottle) the Australian Resuscitation Council (ARC) recommends against the use of vinegar for this species due to evidence, which suggests that vinegar causes nematocyst discharge. The ARC guidelines state that in many cases it may be difficult to identify the jellyfish that caused the sting, so initial management should be geared towards likely organisms based on geographic location, and unless clearly Bluebottle, vinegar is recommended3. Based on ARC guidelines, stings from Bluebottle should be treated as above with tentacle removal and thorough washing with seawater or saline, followed by immersion in hot water (as above) or use of ice packs3.
The slight discrepancy between first aid procedures for envenomation with Physalia species may cause some to delay treatment. The most recent 2010 AHA guidelines are based on the best available experimental evidence and their scientific panel recommends the use of vinegar in all cases of jellyfish stings2. If these recommendations change or undergo refinement, updates to this text will occur.