What Is the Worst a Jellyfish Could Do? Irukandji Syndrome

You may have heard that the Australian Box Jellyfish, Chironex fleckeri, has some of the most potent venom of any animal on the planet, powerful enough to kill an adult human in under two minutes. These animals can grow almost a foot-wide bell, and each animals has up to sixty tentacles, each up to three meters long. Only two meters of tentacles is needed to put the heart in a constant state of contraction, unable to pump blood to the rest of the body, in addition to intense pain that spreads throughout the body. There is no doubt about the awesome potency of C. fleckeri venom.

But let us imagine something just as frightening, perhaps even more frightening, that a jellyfish sting could do. Let’s imagine there is a jellyfish hardly a centimeter in bell-length, with four long, skinny tentacles that can reach almost a meter long. Nearly invisible because of its size and the almost-clear body, the initial sting feels may feel like nothing, a mild poke along exposed skin. But after five, ten, maybe forty minutes later, intense, severe lower back pain, abdominal pain, difficulty breathing, constant vomiting, intense cramps, an unnerving feeling of the skin, a sense of impending doom, and not infrequently, severe hypertension that could lead to heart failure or brain bleeding. A near guarantee of hospitalization, and symptoms that might last for days.  

Well, these animals are very much real. And yes, I said animals – there are several species that can cause the suite of symptoms listed above, known collectively as Irukandji Syndrome. This intense and violent reaction is caused by the sting of the small box jellies in the Family Carukiidae, the most well-known being Carukia barnesi, also called the Common Irukandji, as well as Malo kingi (Pseudo-Irukandji, see below) and other species of Malo, Gerongia rifkinae, and Keesingia gigas. Other box jellies like Morbakka speciesand Alatina alata are also reported to cause “Irukandji-like symptoms,” slightly milder but still painful stingers (Fenner 2006). Even some true jellyfish (scyphozoans) and hydrozoans have been reported to cause similar envenomation syndromes (Gershwin 2016; Tibballs et al 2012).  

Various kinds of Irukandji Jellyfish. Figure 1: Tibballs et al 2012

To really drive home the point, see what a “small bit of tentacle” on the wrist or across the lip will do in this clip from the Biopixel documentary “Killer Jellyfish:”

Or if you just want an audible retelling of what Irukandji Syndrome looks like, start at 16:05 of this podcast from Every Little Thing, which features Dr. Lisa-Anne Gershwin, who has worked with these dangerous animals first hand.

The strange set of symptoms was recognized by the 1940s, called “Type A stingings” by Dr. Ronald Southcott. Irukandji Syndrome was first coined in 1952 by Dr. Hugo Flecker (namesake for the deadly C. fleckeri), who named the syndrome after a local Indigenous Australian tribe near Cairns. The marine animal that caused the syndrome remained unknown until 1964. In his paper “Cause and effect in Irukandji stinging,” toxinologist Jack H. Barnes collected two undescribed box jellyfish near the site of a previous Irukandji Syndrome case. When he observed these animals, he thought the small size and translucent bodies were good candidates for causing Irukandji Syndrome, but instead of moving to animal models, he did something much less conventional (Tibballs et al 2012).

He moved directly to human trials. And the humans were: himself, his 9-year old son (N.B. in the paper), and a “robust young life-saver (C.R.)” that had captured one of the jellyfish specimens (Barnes 1964). After each were stung just under the upper arm, “effects were not long in coming.” Within twenty minutes, the patients were experiencing intense back pain as if it was “boring” into them, and then constant abdominal pains, both common symptoms associated with Irukandji Syndrome. On the drive to the hospital, all three started to have difficulty breathing, and the adults began a constant cycle of abdominal spasms and vomiting. All three survived the experiment, as it were, and recovered after twenty-four hours (Barnes 1964; Gussow 2005). In his honor, the unidentified box jellyfish was named Carukia barnesi, and remains one of the most well-known for causing Irukandji Syndrome. Beyond the Darwin Award winning experimentation on himself and others, Barnes made many additional contributions to the study of box jellyfish toxins, including that of the dangerous C. fleckeri. His life and research are reviewed by Pearn and Fenner in 2006.

You might think that this is only an issue in Australian waters, but species that cause Irukandji-like symptoms, such as Alatina alata, can be found across United States, including Hawaii and Florida. But there is a major concern for Australians – these jellyfish may be expanding their range, according to a recent uptick in hospitalizations. More evidence is certainly needed to see how fast and far (and if) these jellyfish are moving, especially because the ecology and lifecycle of these animals is still poorly understood, in addition to these animals being small and hard to observe during the day. It is difficult to know if these animals have expanded their range, if we have just gotten better at looking, or how future climate trends may play out over the next few stinging seasons.

On average, about 40 people a year are hospitalized in the Northern Territory of Australia from these stingers (according to NT.gov.au), but between 2001-2002, over 100 people presented with Irukandji Syndrome (Tibballs et al 2012). This was also the period of time when the only two official deaths from Irukandji Syndrome were reported, caused by brain hemorrhages from resulting toxin-induced hypertension (summarized in Crew 2013). The first documented fatality was Richard Jordan, a British tourist that may have suffered additional complications because of recent open-heart surgery. No nematocytes, or stinging cells, were recovered from Jordan, but they were from Robert King, a Nestlé researcher from Ohio. King had been in good health before being stung, yet still passed away after being hospitalized on his trip to Australia. Jellyfish use nematocytes to deliver their venom cocktails, but nematocytes can also be used to identify a species; each species has a distinct set of nematocyte types and sizes. The leftover nematocytes on King were examined by Dr. Gershwin, who matched the stinging cells to an undescribed specimen she found in 1999. Published in the journal Zootaxa, she formally described the culprit box jellyfish as Malo kingi, in honor of King’s death (Gershwin 2007).

Interestingly, Barnes had also come across specimens of M. kingi in his own studies, calling it the “Pseudo-Irukandji” because it looked so similar to the Common Irukandji but caused a slightly milder sting. However, this was baed on jellyfish held in captivity prior to Barnes’s trials, so they may have fired numerous nematocytes prior to experiments, weakening their sting. Furthermore, Dr. Gershwin noted that the specimens used in his experiments were quite small, suggesting they may not have been fully grown. Previous studies on C. barnesi and C. fleckeri indicate that as the medusa (jellyfish-stage) ages, it switches diets, and consequentially the venom and nematocyte types and/or distribution adjust to newer, larger prey items like fish (Underwood and Seymour 2007; McCloudin and Seymour 2012). Dr. Gershwin herself said that she has been stung by immature individuals of M. kingi (without gonads or halo-like rings) and suffered no systematic, Irukandji-like effects, though her hands “blistered badly and several layers of skin completely peeled about one week after the sting event” (Crew 2013). If you are saying to yourself, that still seems pretty bad for a JUVENILE animal sting to cause something close to second-degree burns, I am right here with you.

Carukia barnesi, the Common Irukandji. From Wikipedia Commons, CC BY-SA 3.0.

So, what is the venom doing to the human body? Why do we have such a severe reaction? The truth is, it’s quite difficult to determine how exactly these venoms work at a chemical level because you need a fair amount of starting material (i.e. crude venom) to work with. The major difficulty in studying venoms in these animals is their small size, as well as being challenging to collect or maintain in culture (issues I have encountered in my own research on other jellyfish species). That being said, there are several in vivo and in vitro studies on the venom of C. barnesi, which showed the venom contains a sodium channel activator that can cause the release of catecholamines (Winkel et al 2005), which may induce the observed “catecholamine storm” and hypertension observed in a patient reported by Tibballs et al (2001), and later patients as well. This excess catecholamine release can also cause the observed sweating, vomiting, and anxiety (“sense of impending doom”) associated with Irukandji Syndrome. Hypertension was also observed in studies on the cardiovascular effects of C. barnesi venom in rats (Ramasamy et al 2005). These all validate the medical effects of being stung by these animals, but there are still so many questions about how their venoms (and other bits of stinging cells components) cause such physiological chaos in the human body.  

As someone studying jellyfish venom, I am really interested in how the venom of a box jellyfish evolved to result in something strong enough to cause Irukandji Syndrome. What are the ecological roles these toxins play, not only in the medusa but throughout the life cycle? And what about predators, are any components of these venoms used mainly for defensive and those may be what is attacking out bodies in such a strong way? Why does this combination of venom go so horribly wrong when people are envenomated? Box jellyfish catch fish, so their venoms are likely already specialized for vertebrates, which is true of most jellyfish that are able to hurt people. But as Dr. Gershwin points out, it does not make ecological sense for the venom to act several minutes after the initial sting on prey, since the goal it to immobilize and kill quickly. These animals are active hunters, and use the bead-like clumps of stinging cells on their tentacles to attract fish. Fish are quickly immobilized and the tentacles retract to bring the fishy meal to the jellyfish’s “mouth.” Dr. Gershwin noted her own tests on these jellies suggest that fish are not impacted in the same ways that people are, and the reaction humans have could be a random (and highly unfortunate) flip of the coin. Think about it, a venom that acts several minutes after being stung and causes intense pain and spasms does not sound optimal for capturing a fast-moving prey item and immediately trying to digest it. Perhaps it is just a matter of size of the prey (we are much larger than fish), or perhaps the venom is specialized enough that the fish’s heart stops almost immediately after being stung. It is clear that there is still plenty of work to be done on the medical and biological side of these dangerous gelatinous animals.

So, to summarize:

  • There are several stealth jellyfish all over the world that can easily send you to the hospital with unimaginable pain, vomiting, sweating, anxiety, trouble breathing, and possibly hypertension.
  • The discovery of this “Irukandji Syndrome” is based on, I would say, slightly rash experimentation on humans by the discoverer, his son, and a local life guard.
  • We have basic knowledge on how some of these toxins work in the human body, but still relatively poor compared to other venomous animals
  • We still do not have a good grasp on the ecology of these animals and how their venoms are used to capture prey.

For a great review on Irukandji Syndrome, see Tibballs et al 2012.

Cover Image: CC BY-SA 3.0. Wikipedia Commons (https://commons.wikimedia.org/wiki/File:Irukandjijellyfishsize.png)


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