The two groups of jellyfish most dangerous to humans have historically been in the Indian and Pacific (Indo-Pacific) oceans, but are now increasingly being reported in the Caribbean and South American coasts. They are the Box jellyfish
(Chironex fleckeri and other Chironex genus species
), and Irukandji jellyfish (Carukai barnesi and Malo genus species among others
) whose stings can cause severe systemic effects and death. The Portuguese Man-of-War or Blue Bottle jellyfish (Physalia physalis) are typically found in the Gulf Stream of Northern Atlantic Ocean and in tropical regions of Indio-Pacific oceans. Blue Bottle jellyfish are actually not a true jellyfish but a colonial hydrozoan. They can deliver an extremely painful sting with systemic effects, but rarely cause death. With increasing ocean temperatures and frequent tropical storms occurring in the U.S. East Coast
and Gulf Coast
there are now frequent annual sightings of Portuguese Man-of-War, and even reported far north in Halifax, Canada during the summer months. Due to the morbidity and mortality associated these three species, most research has focused on treating their stings.
Depending on species, a sting can range from minor skin irritation to excruciating severe pain that may include systemic symptoms including anaphylaxis, cardiorespiratory shock, rapid paralysis and neurogenic shock. The Indo-Pacific Box jellyfish (Chironex fleckeri
) is considered to be the most lethal jellyfish worldwide and can cause death within minutes. It is estimated that approximately 100 people die per year (majority in the Philippines) from venom so potent that a single jellyfish contains enough to kill >60 people (Note: Antivenom exists, though its efficacy is controversial). There are additional less lethal Box jellyfish that can be found in Atlantic, Caribbean and Pacific waters, and can also deliver a dangerous and painful sting.
A second group of tiny box jellyfish species collectively known as Irukandji jellyfish (approximately 20 species discovered thus far including Carukai barnesi, Malo, and Carybdea species
) are also getting increased notoriety due to life threatening stings that cause Irukandji Syndrome. Named after the Irukandji Indigenous Peoples of Northeastern Australia in which the syndrome was first observed, these potent stings cause massive catecholamine release and present with life threatening hypertension, severe back and abdominal pain, chest pain, vomiting, tachycardia, cardiopulmonary collapse, and death.
Jellyfish tentacles have stinging cells known as cnidocytes that contain penetrating venom organelles known as nematocysts. Each capsule-like nematocyst houses a hollow coiled barbed tubule that is deployed in a dart like manner to inject venom into the victim when triggered. They can be triggered by direct pressure or via chemoreceptor activation. There are potentially hundred thousand or more nematocysts lining the tentacle (based on length), each containing its own tiny trigger and venom apparatus. See an excellent video
presentation for all age groups showing a jellyfish sting animation, along with a microscopic slow-motion video of nematocysts injecting venom. Understanding the mechanism of jellyfish envenomation is important as it drives the rationale behind up-to-date medical management recommendations.
The morbidity and mortality related to jellyfish stings has motivated clinical researchers to seek solutions. Research has concentrated primarily on 1) development of improved antivenom, 2) development of topical sting preventatives, and 3) development of more effective first aid treatment algorithms for post sting management. Here we will concentrate on up-to-date evidence based first aid treatment, as antivenom and topical sting preventatives are still controversial areas in need further research. Past treatment recommendations caused much confusion, (e.g., to pee or not to pee; use of ice versus heat application; and to either rub, scrape, shave or pluck). See Table 1 below for a wide range of historic recommendations to manage jellyfish stings, many of which are now known to worsen stings. See Table 2 for common jellyfish myths.