Excerpt from Jellyfish Stings

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Background

With more than 10,000 species in the sea, jellyfish are responsible for the most common human envenomations. More than 100 species are toxic to humans, and contact with toxic jellyfish causes a wide range of conditions, from cutaneous rashes to cardiovascular and respiratory collapse.

Jellyfish are categorized into 4 classes as follows:

• Hydrozoa (Portuguese man-of-war)
• Scyphozoa (true jellyfish; most common)
• Cubozoa (box jellyfish; most toxic)
• Anthozoa (sea anemones and corals)

Jellyfish have a single gastrovascular cavity opening, which is used for digestion and circulation, and a set of tentacles. The tentacles are covered with batteries of specialized stinging cells termed nematocytes. Each nematocyte contains a stinging apparatus known as the nematocyst. This stinging apparatus basically consists of a poison sac with an attached sharp hollow tube armed with barbs.

Detached tentacles found on the beach pose a hazard to humans because they remain capable of envenomation for several weeks.

Pathophysiology

The stinging process of the nematocyte resembles a jack-in-the-box mechanism. Specifically, mechanical and chemical stimulation of the sensory hairs (ie, cnidocil) surrounding the pressurized nematocyte results in a calcium-mediated bioelectric signal that causes an opening of its lid, allowing the ejection of the nematocyst into the prey to express the venom. This pressurized process has a high internal hydrostatic pressure of 150 atm that causes the ejection to occur within 3 milliseconds, with an acceleration power of 40,000g and a force of penetration of 20-33 kPa. In addition, the nematocyst is capable of penetrating up to a depth of 0.9 mm. This depth deposits the toxin into the microvasculature of the dermal tissue to be absorbed into the systemic circulation and anchors the tentacles to the prey. Finally, the nematocyte must be replaced because it cannot regenerate the ejected nematocyst. This replacement is done via differentiation of the pluripotent cells.

Nematocysts

The nematocysts' size and arrangement on jellyfish tentacles differ from species to species, much like a fingerprint. This architectural arrangement of warts, ridges, spirals, and terminal swelling may be reflected in the skin pattern left via the sting and helps identify the species involved in the envenomation.

Toxin

Microscopically, nematocysts appear structurally similar from one species to another, but the venom differs in composition. For example, because the box jellyfish feeds on fish larger than its own body, it requires potent venom for rapid paralysis. While the amount of toxin expressed by a single nematocyst is minute, several thousand nematocysts discharging at once have a significant effect.

Functionally, the toxin causes sodium and calcium ion transport abnormalities, disrupts cellular membranes, releases inflammatory mediators, and acts as a direct toxin on the myocardium, nervous tissue, hepatic tissue, and kidneys.

Specifically, the toxin may contain catecholamines, vasoactive amines (eg, histamine, serotonin), kinins, collagenases, hyaluronidases, proteases, phospholipases, fibrinolysins, dermatoneurotoxins, cardiotoxins, neurotoxins, nephrotoxins, myotoxins, and antigenic proteins. The protein component of the toxin tends to be heat labile, nondialyzable, and is degradable by proteolytic agents.

Reaction to venom

Immediate acute reactions to the venom tend to be toxic rather than allergic. Since pain occurs immediately after exposure, venom injection into different mammals induces similar clinical results, and victims can be stung repeatedly without differences in symptoms. The more rapidly the venom gets into the bloodstream, the higher the venom concentration in blood and the more rapid the onset of systemic symptoms. Delayed reactions to jellyfish stings are related immunologically, as evidenced by persistent immunoglobulin G (IgG) levels, prolonged T-cell response, and cross-reactivity among various jellyfish venom antigens.

Frequency

United States

Jellyfish stings occur most commonly during the summer along coastal regions. As the coastal population grows and more tourists come to the beaches, the frequency of jellyfish sting is likely to increase. One investigator reported 500,000 annual envenomations in the Chesapeake Bay area and 200,000 annually along the Florida coast.

International

Jellyfish stings occur in tropical oceans, especially between latitudes 30° south to 45° north, because of a high natural concentration of coelenterates. This is especially true of the east coast of Australia during the warm summer months between November and May.

Mortality/Morbidity

Jellyfish stings usually are mild, except those caused by species in the South Pacific, such as the box jellyfish or Portuguese man-of-war. Exact mortality and morbidity is not known because of underreporting and the lack of an international jellyfish sting registry. However, a recent epidemiology study of 118 cases of jellyfish stings from the Texas gulf coast showed 0.8% had no effect, 80.5% had minor effects, and 18.6% had moderate effects.

• Box jellyfish venom has a median lethal dose of 40 mcg/kg, which makes it the most potent marine toxin. The venom may kill a person weighing 70 kg within 3 minutes and is responsible for a mortality rate of 20%. Box jellyfish venom has caused 72 deaths secondary to respiratory paralysis, neuromuscular paralysis drowning, and cardiovascular collapse.
• The sting of the Portuguese man-of-war is more painful than a common jellyfish sting. It has been described as feeling like being struck by a lightning bolt, and some victims dread it more than a shark bite. This sting has been responsible for 2 reported deaths.
• The Arctic jellyfish is the largest, with tentacles reaching 200 ft, allowing the jellyfish to sweep an area slightly larger than a basketball court.

Race

No racial predilection exists. Any differences in individual reactions to jellyfish are a reflection of immune status rather than race.

Sex

• Men are more likely to be stung than women because they are more likely to participate in water activities such as surfing, sailing, saltwater fishing, and scuba diving.
• Lower body weight makes women more susceptible than men to the same amount of jellyfish venom.

Age

• Children are most susceptible to the effects of toxins because of their large surface area–to–volume ratio and lower body weight.
• Older adults are more susceptible than younger adults because of their decreased physiologic reserves and concurrent debilitation.

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