Jellyfish Envenomation: Summer Toxicities

Yet, until very recently, understanding of jellyfish sting toxicity has remained limited. Upon contact, jellyfish stinging cells discharge complex venoms, through thousands of barbed tubules, into the skin resulting in painful and, potentially, lethal envenomations. Jellyfish venoms are composed of potent proteinaceous porins (cellular membrane pore-forming toxins), neurotoxic peptides, bioactive lipids and other small molecules whilst the tubules contain ancient collagens and chitins. In subsequent years, numerous clinical observations and experiments have established that the toxins of numerous jellyfish species provoke a variety of immunological responses.

Mechanism of Singing

The word “jellyfish” refers to the free-floating medusal gelatinous lifecycle stage of members of the phylum Cnidaria. A defining feature of this ancient phylum is the cnidae, a remarkably specialized, explosive organelle elaborated by the Golgi apparatus and comprised of a collagen-walled capsule containing a rapidly eversible penetrant or non- penetrant tubule. Specialised cnidae producing penetrant “stinging cells” termed nematoblasts, each synthesise a singular nematocyst containing a micron-diameter eversible spine-laden tubule of approximately 200 to 800 micron length allowing the deposition of capsular contents or “venom” for the purposes of defence and capture of prey.

Upon physical contact, the capsules of the nematocysts (“spring-loaded syringes”) fire a barbed arrow-like tubule within 700 ns of physical contact at high velocity (18.6 m/sec) and acceleration (5.4 × 106 g) creating a pressure of 7.7 GPa at the site of impact. Upon contact with human skin or other surface (e.g., cornea), thousands of tubules transporting toxins are deposited per square centimetre of the epidermis and dermis. The combined physical impalement by barbed tubules and deposition of potent venom toxins quickly immobilize and kill prey. In humans, toxins cause local and systemic injury and may also provoke immunological responses. The length of the penetrant tubules of some species renders possible the direct deposition of venom toxin into pierced capillaries thus explaining the rapid onset of toxicity in humans. In addition to envenomation, stings embed spine-laden tubules which are composed of ancient mini-collagens, glycoproteins and polysaccharides. These substances may trigger in addition antigenic, allergenic and innate immune responses.

Cutaneous toxic and immune responses to stinging

The deposition of the complex mixture of nematocyst constituents, venom, carried by jellyfish tubules probably sets off a complicated system of cellular and cytokine interactions analogous to that described on entry of pathogens or allergens into human skin.

Although keratinocytes are the front line protective defence against physical incursion into the skin, they also have another role which is to release thymic stromal lymphopoietin which activates T-cells to produce cytokines, known to be prominent in allergic dermatitis. Dendritic cells, a heterogeneous population of lympho- myeloid origin critical to the initiation of immune responses, capture and present antigens to T-cells or migrate to regional lymph nodes evoking immune or delayed hypersensitivity allergic reactions. Mast cells are potent drivers of inflammation, releasing biogenic amines such as histamine and other substances including platelet activating factor, prostaglandins, leukotrienes, proteases and cytokines into their tissue environment when stimulated.

Although the medusal floats are clearly visible, tentacles trail many metres unseen beneath the surface and represent a threat to unwary swimmers, and their nematocysts can still discharge if handled out of water. The stings of these species, which resemble a “string of beads”, cause sharp pain which may extend beyond the site of the immediate lesion. The pain usually subsides quickly and the sting fades within hours to days. Occasionally however, the wound may blister and a systemic illness consisting of headache, vomiting, abdominal pain and diarrhoea is provoked. Some evidence exists that stings by this jellyfish may provoke immediate and delayed hypersensitivity responses: rapid collapse and immediate hypersensitivity. The few deaths following stings in Atlantic waters have been attributed to cardiovascular toxicity.

Bather’s Eruption in Florida, Bahamas and Western Caribbean

This pruritic papulopustular dermatosis has occurred among bathers in waters in the Bahamas, the Western Caribbean or off southern Florida. The affliction is often confined to areas of skin which had been covered by clothing. The agent responsible is any of the three free-swimming or larval stages (ephyrae, medusae, planulae) of the minute “thimble jellyfish” Linuche unguiculata.

Contact with the creature is not painful but a prickling or stinging sensation may be experienced while the victim is in the water followed later by severe itching. This toxic component of the illness is followed by an immunological component consisting of an urticarial eruption and a distressing dermatitis which may last many days to several weeks. There is no specific treatment for seabather’s eruption. Local antipruritic agents and analgesic agents afford relief but opinions differ concerning the efficacy of topical and systemic steroids and antihistamines are opined not useful.

Summer Take Home Message

When deposited in the skin of sting victims, these complex venoms some components of which are cytolytic proteins, cause local pain, skin lesions and distal effects in many human organ systems although rarely fatal. Some venom components are also antigenic and may trigger an acute hypersensitivity immune response from which acute toxic responses are difficult to differentiate. Delayed hypersensitivity responses may also be promoted and these manifested in the skin as persistent, recurrent, vesicular or pruritic dermatitis for which newer agents such as the topical immunomodulators may be beneficial. The numerous other illnesses following jellyfish stings may be either toxin or immune-based, or both. Jellyfish stings also deposit in the skin foreign structural biopolymers including chitin and mini-collagens that we speculate may contribute to the resultant host immune response.


Each Jellyfish envenomation can cause local but also systemic effects. Therefore it remains important to take each incident serious. Local treatment consists of calming down the allergic symptoms such as urticaria, pruritus, itching, swelling and prevention of surinfection by flushing the wound with sea water solution and avoid additional sun light and beach activities that day. Additional skin lesions may appear such as blisters. The patients should be checked for any systemic illness such as headache, vomiting, abdominal pain or diarrhoea.

In tropical areas there is certainly a higher risk for envenomation with severe life threatening symptoms which need immediate medical intervention. In case of a cardiac arrest, the use of extracorporeal life support combined with good quality cardiopulmonary resuscitation may offer the only realistic hope of a full recovery of an envenomated victim.

Therefore, it remains important to check all warning signs when going to a beach and only swim in protected zones with surveillance. Swimming covered by clothing does not always protect as ‘thimble jellyfish’ can be easily trapped in or beneath clothing.