MARINE VENOMOUS CREATURES
The sea is host to a wide variety of venomous creatures which sting or bite, and are a special threat to swimmers and divers. Marine envenomations have risen sharply in incidence over the last few decades owing to an increase in popularity of recreational diving and other water related sports.
Approximately 225 species of marine fish are known to be venomous. These include the stingray, scorpionfish, lion- or zebra-fish, stonefish, weeverfish, toadfish, stargazer, and certain catfish, sharks, ratfish, and surgeonfish. The most common marine envenomations are caused by fish belonging to family Scorpaenidae of class Osteichthyes and order Perciformes. Venomous fish produce envenomation by means of their spines, fins, or caudal stings.
In most cases, the stung victim experiences severe burning pain and swelling within seconds of the sting. Systemic symp-toms include nausea, vomiting, hypotension, and rarely cardiac arrhythmias. Stings from a stingray can result in severe lacera-tions with tendency to necrosis. There is intense pain, associated with paraesthesias, nausea, vomiting, abdominal pain, cardiac arrhythmias, and convulsions. Limb paralysis may be seen with severe envenomations.
Treatment involves the following measures:
· Soaking the affected limb in hot water (110° to 115° F).
· Paracetamol, salicyclates, non-steroidal anti-inflammatory drugs, or opiate analgesic for pain, depending on the severity.
· Tetanus prophylaxis.
· Wound care.
· Supportive measures.
· There are two important phyla of venomous marine inverte-brates: Coelenterata and Echinodermata. Less common inver-tebrates which cause envenomation include molluscs such as cone shells and octopuses.
Coelenterates account for most of the reported cases of marine envenomations around the world, and comprise more than 9,000 species of which approximately 100 belonging to Cnidaria are venomous. The Cnidaria are subdivided into 3 classes: Hydrozoa, Schiphozoa, and Anthozoa:
Portuguese man-o’-war (Physalia sps).
Jellyfish (“box jelly”, “fire medusa”) (Chironex fleckeri)
Most of the Cnidaria possess stinging structures called nema-tocysts or cnidocytes, which are poisonous dart-like structures, tightly coiled and enclosed within venom sacs. Following external contact, they are expelled from the sacs, injecting venom as they penetrate the flesh of their prey. The venom is a complex mixture of serotonin, histamine, bradykinin, haemolysin, pros-taglandins, hyaluronidase, phosphodiesterases, fi brinolysin, RNAase, DNAase, adenosine triphosphatase, alkaline and acid proteases, as well as alkaline and acid phosphatases.
Envenomation usually results in local burning pain with erythematous or violaceous lesions, and regional lymphad-enopathy. Erythema nodosum, arthralgias, and anaphylactoid reactions have also been reported. Delayed hypersensitivity reactions may occur, consisting of a pruritic erythematous maculopapular rash appearing at the initial tentacle contact points, usually in 7 to 14 days after envenomation. The reac-tions spontaneously resolve in some patients, while others recover following treatment with oral antihistamines and topical corticosteroids.
The box jellyfish, fire medusa, or sea wasp (Chironexfleckeri) (Fig 12.54) is the most venomous of all stinging marinecreatures. It has a transparent box- like bell with four pedalia (feet). Each pedalia may have up to 15 tentacles attached. Because of its transparency, the box jellyfish is virtually invis-ible under natural conditions, including clear, sunlit seawater. When fully grown, the bell of Chironex fleckeri may measure up to 30 centimetres in diameter, weigh up to 6 kilograms, and the total length of its tentacles may be greater than 60 metres. Chironex fleckeri is predominantly found in northern Australian waters. Each box jellyfish carries enough venom to kill several adults. Features include profound muscle spasm, hypotension, acute respiratory distress, respiratory paralysis, cyanosis, haemolysis, arrhythmias, and cardiac arrest. Severe parasympathetic dysfunction (abdominal distension, urinary retention, dry eyes) is common. Death can occur in less than a minute. A few cases have been reported from India also. Neuromuscular paralysis leading to respiratory arrest may occur following Chironex fleckeri stings. The sting of a chirodropid is characteristic for leaving a “cross-hatched” or “frosted-ladder” tentacle imprint on the skin, as well as multiple wheals. The skin may become blackened, and permanent scarring may result.
· Anaphylaxis to jellyfish sting must be treated by main-taining airway and cardiovascular status. Adrenaline is administered in the usual way. Verapamil may be useful for arrhythmias. Antihistamines with or without inhaled beta agonists, and corticosteroids may be required. Topical corticosteroids and oral antihistamines are indicated in delayed hypersensitivity reactions.
· Remove any adhering tentacles carefully without too much tactile pressure which may cause additional nematocyst discharge. Do not rub the affected area.
· Inactivate unexploded nematocysts by topical application of any of the following solutions for at least half an hour:
o Vinegar (3 to 5% acetic acid). Altering pH below 6 inactivates the venom.
o A slurry (50% w/u) of sodium bicarbonate or baking soda. Altering pH above 8 dissolves tentacles.
o Aluminium subacetate 10 to 20% (Burow’s solution). The aluminium ion denatures protein constituents of venom. Adding 5% detergent enhances efficacy.
o Meat tenderiser (papain). It causes denaturation of protein constituents, but is not as effective as aluminium subacetate.
· Apply dry baking soda, flour, sand, or shaving soap to the affected area.
· Scrape off remaining nematocysts from the wound with a knife.
· Wash the area with seawater: Bathe the affected part liberally with seawater. Do not use fresh or hot water, or alcohol. Fresh water/alcohol may discharge nematocysts and therefore should be avoided.
· Apply a steroid cream or lotion (e.g. triamcinolone 0.1%). If the lesion ulcerates, clean daily with Burow’s solution and cover with dry dressings.
· Administer tetanus prophylaxis.
· For pain: Apply ice-packs for initial pain relief combined with IV or IM analgesics, if necessary (1 mg/kg of pethi-dine up to 50 mg, or morphine, 0.1 mg/kg up to 5 mg; can be repeated).
· Painful muscle spasms may be relieved by calcium gluco-nate 10% IV.
· For hypotension: Infuse 10 to 20 ml/kg of isotonic fluid and place in Trendelenburg position. If hypotension persists, administer dopamine or noradrenaline. Institute central venous pressure monitoring to guide further fluid therapy.
· For box jellyfish envenomation, specific antivenom is available (Commonwealth Serum Laboratories, Melbourne, Australia). It should be given in life-threatening stings, or severe stings where the pain is not controlled by other methods. The antivenom should preferably be given within 4 to 6 hours.