Jellyfish Envenomation

By Nicholas Ward, MD, Michael Darracq, MD, and Binh Ly, MD

Introduction

Jellyfish (Scyphozoa) are delicate soft-bodied animals in the phylum Cnidaria. While they are found in virtually coastal water zones worldwide, jellyfish populations fluctuate greatly is association with ocean climate and perhaps other factors related to human interactions with the oceans. A 2012 publication in the journal Hydrobiologia suggests that jellyfish populations off the coast of California are on the rise. Despite their abundance globally, jellyfish are infrequently studied for their toxic effects on humans.

How do jellyfish cause toxicity in humans?

Jellyfish are highly variable in size and have stinging structures called nematocysts attached to thin tentacles that trail behind the bell atop the organism. Nematocysts are harpoon-like structures that are tightly coiled within venom sacs and deployed upon contact with other organisms including marine-life and humans. In general, jellyfish venom is a complex mixture of enzymes, inflammatory mediators, polypeptides, neurotransmitters among other components. Jellyfish stings are not typically medical emergencies, but can be very painful. Anaphylactoid reactions characterized by bronchospasms and cardiovascular collapse have been reported but rare. Although the most serious envenomations occur in the waters of the Indo-Pacific region, North American and European waters also provide a habitat for jellyfish and stings are reported regularly. In August 2007, lifeguards in San Diego estimated 200 jellyfish stings citywide per day.

How are jellyfish envenomations treated?

Many folk remedies include vinegar, meat tenderizer, and hot water has been suggested. Some even advocate urinating on the envenomation site.

Currently recommended treatments for stings involve two distinct yet ideally simultaneous strategies. One is to reverse the pain and tissue damage from the venom itself. The second is to prevent further discharge of venom-laden nematocysts to allow their eventual removal intact. Some therapies might be successful at the former but fail or worsen effects with regard to the latter.

There is not a lot of research available on the treatment of jellyfish stings with most conducted in Australia. Currently, the American Heart Association and American Red Cross recommend vinegar or baking soda slurry, followed by heat or ice. These recommendations, however, are based mainly on studies of jellyfish species not commonly found in North American waters. Several reports have recently suggested some of these treatments, including vinegar, may in fact worsen a sting. Vinegar is no longer a first-line recommended therapy in Australia as a result of this controversy.

Probably the most important thing to do following a jellyfish sting is to first remove the tentacles and nematocysts (stinging cells on the tentacles) from the skin. Jellyfish leave behind nematocysts that should be scraped off as soon as possible, since they have the potential to still discharge remaining venom. One option is to carefully remove the nematocysts with the edge of a credit card or something similar with care to avoid crushing the sac containing nematocyst and venom. Caution should also be exercised to avoid touching tentacles with a bare hand.

A review of 19 in vitro, animal, and clinical studies conducted by Ward and colleagues in 2012 suggests after removing the remaining nematocysts the best options for treatment, may be hot water or topical lidocaine. The mechanism of action of hot water is not well understood but may be related to reducing venom activity. Local anesthetics block sodium channels and thereby the excitability of sensory neurons. The application of local anesthetics would be expected to reduce the local sensation of pain. Lidocaine treatment may result in immediate relief or at least a reduction in the stinging sensation caused by envenomations from Chiropsalmus quadrumanus and Chrysaora quinquecirrha. Benzocaine dissolved in ethanol may provide some relief from jellyfish stings but may take 10 minutes or longer to do so.

Lidocaine cream or hot water may not be readily available when a jellyfish strikes. In this situation, removing the venom sacs from the skin and washing the area with saltwater may be the best option available.

Common remedies with alcohol, acids, and urea (urine), however, were found to precipitate nematocyst discharge or not result in pain improvement following envenomation from several species of jellyfish common to North America and Hawaii, including the sea nettle (C. quinquecirrha), Atlantic Ocean Portuguese man-o’-war (P. physalis), hydroid (L. philippinus), and mauve stinger (C. capillata).

There are significant discrepancies in effective remedies for different species contributing to the confusion about what therapies to suggest. Specifically, there have been mixed results with vinegar. Although formerly considered effective, in laboratory experiments vinegar caused discharge of nematocysts from the larger man-of-war species (P. physalis) but mixed results in the smaller species (considered to have less severe stings). In North America, Portuguese man-of-wars are found primarily off the coast of Florida and in the Gulf of Mexico. However, with stings from most species native to North America and Hawaii, vinegar may actually worsen pain or cause any remaining venom sacs to discharge.

Questions

1. Where are jellyfish found?
2. What are the symptoms and signs of jellyfish envenomation?
3. What are the two main objectives in treating jellyfish envenomations?
4. True or false – vinegar may be harmful when used to treat evenomation from species found on the coast of California.
5. Based on the currently available literature, what interventions may be recommended for the treatment of jellyfish envenomations?

Answers

1. Jellyfish are found in coastal waters worldwide.
2. PAIN is the main symptom but bronchospasms, hypotension, and shock may result from reactions.
3. Reverse toxic effects of venom and preventing further envenomation resulting from discharge of intact nematocysts in contact with the victim are the two main objectives in treating jellyfish stings.
4. True.
5. Hot water and topical anesthetic such as lidocaine are the interventions supported by the currently medical literature.

Conclusion

Additional research is necessary to clarify the optimum treatment for jellyfish stings in North America. With the current research available, the best options are lidocaine or hot water. In the absence of these interventions, removing tentacles with saltwater is recommended. Vinegar cannot be routinely recommended for species common along the coast of California but may be indicated with exposures in Florida and the Gulf of Mexico.