Cnidaria Envenomation
- Author: G Patrick Daubert, MD; Chief Editor: Scott H Plantz, MD, FAAEM more...
Background
Cnidaria (formerly Coelenterata) are in the phylum of aquatic invertebrates responsible for more envenomations than any other marine phylum. Close to 9000 species of Cnidaria are known, of which approximately 100 are toxic to humans. These animals have a gastrovascular cavity with a single opening used in digestion and circulation. Another characteristic feature is the presence of stinging cells or nematocysts.
Human envenomations occur from all 4 classes in this phylum: (1) Hydrozoa (Portuguese man-of-war and fire coral), (2) Scyphozoa (true jellyfish), (3) Cubozoa (box jellyfish), and (4) Anthozoa (soft corals and sea anemones) (shown in the image below).
Cnidaria and jellyfish envenomations. Close-up photograph of a sea anemone demonstrating one of several tentacle types observed among different species. Photo courtesy of Scott A. Gallagher, MD. Of the many toxic species, 3 species or conditions deserve attention because they are life-threatening or extremely common: the box jellyfish Chironex fleckeri, the carybdeid Carukia barnesi (Irukandji syndrome), and the bluebottle or Portuguese man-of-war.
Pathophysiology
The toxin of Cnidaria is located in cnidocytes, which are stinging cells composed of organelles called nematocysts. Nematocysts are present on the outer surfaces of tentacles or near the mouth (this is shown in the image below).
Cnidaria and jellyfish envenomations. Close-up photograph of sea anemone demonstrating tentacles surrounding the central mouth structure. Contact with tentacles results in discharge of nematocysts. Photo courtesy of Scott A. Gallagher, MD. Nematocysts are contained within the cnidoblast or the outer capsule. On the external surface of the cnidoblast is the cnidocil (trigger point), which can be triggered by mechanical or chemical stimuli or may have remote and local control. At the base of the cnidocil is a hollow, coiled, sharp, threaded tube containing venom. The threaded tubes have denticles, which give the uncoiling thread cutting power like a drill. Extruded threads may reach up to 1 mm in length, a distance that is sufficient to penetrate the dermis of human skin. It is currently believed that the explosive release of the thread is caused by a sudden release of springlike tensions stored in the collagenous structural compartment. This is likely due to the sudden removal of bound calcium ions, resulting in a sudden increase in osmotic pressure in the capsular fluid.
The venom of many species is complex and largely unknown. The majority of toxins contain a complex mixture of polypeptides and proteins including (1) catecholamines, (2) histamine, (3) hyaluronidase, (4) fibrinolysins, (5) kinins, (6) phospholipases, and (7) various hemolytic, cardiotoxic, and dermatonecrotic toxins.
Hydrozoa class
The Hydrozoa class contains Physalia species (ie, Portuguese man-of-war or bluebottle) and hydroid corals. Portuguese man-of-war is not a true jellyfish but rather a siphonophore colony of hydrozoans with 4 different groups of animals. The result is a free-swimming organism with tentacles hanging from a gas-filled float, which acts as a sail, allowing wind-assisted travel. At least 2 Physalia species are of importance: (1) the larger Physalia physalis, which is found in the Atlantic Ocean from Nova Scotia to the Caribbean Sea; and (2) the smaller Physalia utriculus, which is found in the Pacific and Indian Oceans. Tentacles may reach up to 100 ft in length and contain up to a million nematocysts.
Detached tentacles on the beach are hazardous because they are capable of releasing venom for several weeks. Physalia species are one of the most commonly encountered marine envenomations in the United States and South Pacific. At least 3 confirmed deaths are attributed to P physalis.
Fire corals (Millepora) are typically encountered off the Florida coast and in the Caribbean and produce minimal toxicity, predominantly local pain.
Hydroid corals are sessile creatures that can attach to rocks, coral, seaweed, or pilings. A typical reaction is a mild stinging sensation with occasional development of burning pain and lymphadenopathy.
Scyphozoa class
The Scyphozoa class contains true jellyfish. In the United States, true jellyfish are the most common Cnidaria species to cause envenomation. Sea nettles Chrysaora species and Cyanea species are located along the Atlantic coast, with a high concentration near the Chesapeake Bay. Envenomations caused by organisms in the class Scyphozoa are less severe than those caused by Portuguese man-of-war.
Cubozoa class
The Cubozoa class contains the most toxic marine organisms, box jellyfish (Chironex fleckeri) and sea wasp (Chiropsalmus quadrigatus). The box jellyfish is the most dangerous jellyfish known with at least 67 deaths attributed to its envenoming. They are known to move into shallow waters in pursue of prey, thereby invading popular swimming areas. It is the only jellyfish with an antivenom. These animals are found in northern Australia and have not been reported in North American waters.
Carukia barnesi is also in this class and produces Irukandji syndrome. The mechanism of Irukandji syndrome is not known. Although only C barnesi is conclusively known to cause this condition, a number of other jellyfish are also likely responsible. The venom of C barnesi contains a sodium channel modulator that is linked to increased catecholamine release, which explains the early hyperadrenergic state demonstrated by these patients. The mechanism for cardiac dysfunction is yet to be elucidated as to whether it is the result of a myotoxin, due to excessive catecholamines, or both.
Anthozoa class
Anthozoa class contains sea anemones and corals. Most Anthozoa organisms are sessile creatures, and anemones found within the United States tidal zones have minimal toxicity. The sea anemone Phyllodiscus semoni (night or wasp-sea anemone) located in the Western Pacific Ocean is reported to cause fulminant dermatitis and acute renal failure in humans.
Corals
Corals are important components of living reefs. Risk of infection from a coral cut is of greater concern than the toxic effects of the coral.
Epidemiology
Frequency
United States
Jellyfish envenomations occur in coastal areas of the United States, with highest frequency during summer. Envenomations by Physalia species are the most common jellyfish encounter prompting evaluation in the emergency department. Cases of seabather's eruption occur in clusters along the East Coast and Caribbean.
International
An estimated 40,000-50,000 marine envenomations occur annually. Approximately 10,000 Cnidaria envenomations occur each summer off of the east coast of Australia, the vast majority of which are due to Physalia species. Each season, the Royal Darwin Hospital in Australia treats more than 40 patients with jellyfish encounters. A prospective evaluation of envenomings from that hospital over a 12-month period from 1999-2000 revealed that 70% resulted from the box jellyfish.[1] The remaining 30% mostly involved other Cubozoa species. This study may suggest that box jellyfish envenomings are common but also suggests the severity of the encounters. Many beaches in Australia have large amounts of vinegar placed in prominent positions along swimming beaches in jellyfish-endemic areas. This likely reduces the amount of emergency department visits for mild-to-moderate encounters.
Mortality/Morbidity
Fatal envenomations due to box jellyfish occur in tropical waters of northern Australia. Fatalities have occurred rapidly, within 60 seconds, from this species. At least 67 deaths have been attributed to the box jellyfish.
At least 3 deaths have occurred due to Physalia species since 1989 in the United States.
In addition, a 4-year-old boy died within 40 minutes from an apparent envenoming by the jellyfish Chiropsalmus quadrigatus in the Gulf of Mexico.[2]
Most patients who develop Irukandji syndrome recover within 1-2 days, but 2 deaths were reported in Queensland, Australia, in 2002.
Patients have reported delayed hypersensitivity reactions as well as hypopigmented and hyperpigmented areas in the regions of the original tentacles.
Race
No scientific data substantiate any differences in Cnidaria envenomation that are attributable to race.
Sex
No scientific data substantiate any differences in Cnidaria envenomation that are attributable to gender.
Age
Although not well studied, a large number of pediatric cases are reported in the literature, likely due to the shallow water swimming. The smaller body mass and thinner skin may make infants and children more susceptible to jellyfish envenomations.
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