Marine Envenomation

Marine envenomation by vertebrates and non-cnidarian invertebrates includes stingrays, venomous catfish and weeverfish, cone snails, the blue-ringed octopus, sea urchins and sea snakes. Most injuries occur in shallow water and on beaches. Venoms are mostly heat-labile proteins, so hot water immersion relieves pain in many of them. Wounds are often contaminated with marine bacteria, including Vibrio, Aeromonas, Staphylococcus, Streptococcus and, weeks later, Mycobacterium marinum.

Syndromes

• Stingray: a barbed spine produces a jagged laceration, venom pain and retained spine fragments. Penetration of the chest or abdomen can be fatal.
• Cone snail: conotoxins block neuromuscular transmission and cause paralysis. Mortality is about 25% without ventilation.
• Blue-ringed octopus: tetrodotoxin causes paralysis within minutes with preserved consciousness.
• Sea urchin: spines break off in the skin and joints and cause granulomas.
• Sea snake: myotoxic, neurotoxic and nephrotoxic venom, with a painless bite and symptoms after 30 minutes to 3 hours.

Complications: respiratory failure, rhabdomyolysis, hyperkalemia, acute kidney injury, coagulopathy, wound infection, retained foreign body, osteomyelitis and chronic granulomas.

• Stingray: immediate severe pain out of proportion to the wound, bleeding, swelling, ischemic wound edges, nausea, vomiting, syncope and hypotension
• Cone snail: stinging pain, local numbness, then perioral tingling, weakness, paralysis and respiratory failure
• Blue-ringed octopus: a painless bite, then numbness, paralysis and respiratory arrest within 10 minutes
• Sea urchin: puncture wounds, bluish discoloration from the dye, pain, and joint swelling if spines enter the capsule
• Sea snake: muscle pain and stiffness, trismus, ptosis, dark urine, hyperkalemia and respiratory weakness
• Red flags: chest or abdominal penetration, weakness, respiratory difficulty, dark urine and a deep wound over a joint

1. History and examination of the wound and neurological function.
2. Radiographs: retained spines in stingray and urchin injuries. Ultrasound for non-opaque fragments.
3. Sea snake bites: 20-minute whole blood clotting test, coagulation studies, creatine kinase, potassium, creatinine and urine myoglobin.
4. ECG, blood gases and vital capacity when weakness develops.
5. Wound cultures if infected, and acid-fast culture for chronic nodules.

Differentials: jellyfish sting, stonefish envenomation, other penetrating marine injury, fracture, tetrodotoxin poisoning, neurotoxic snakebite.

1. Immediate care: remove the patient from the water, control bleeding with direct pressure, and irrigate with saline.
2. Hot water immersion at 45 degrees Celsius (test on an unaffected limb) for 30 to 90 minutes for stingray, urchin, scorpionfish and catfish injuries.
3. Pressure immobilization bandage and rest for cone snail, blue-ringed octopus and sea snake bites.
4. Analgesia: paracetamol 1 g orally every 6 hours, morphine 0.05 to 0.1 mg/kg IV titrated, and lidocaine 1% infiltration without epinephrine (maximum 4.5 mg/kg) or regional block.
5. Wound care: explore under anesthesia, remove foreign material, debride and leave the wound open for delayed closure. Tetanus toxoid 0.5 mL IM if not immunized.
6. Antibiotics for deep or contaminated wounds: doxycycline 100 mg orally twice daily with ciprofloxacin 500 mg orally twice daily for 5 to 7 days (children under 8 years, co-trimoxazole 4 mg/kg of trimethoprim twice daily).
7. Sea snake bites: sea snake antivenom 1000 units IV over 30 minutes, repeated after 1 to 2 hours if features persist (up to 3 ampoules), with IV crystalloid to keep urine output over 1 mL/kg/h. Hyperkalemia: calcium gluconate 10% 10 to 20 mL IV and insulin 10 units IV with 50 mL of 50% dextrose. Haemodialysis for kidney failure.
8. Cone snail and blue-ringed octopus: no antivenom. Intubate and ventilate until paralysis resolves (4 to 12 hours for the octopus, up to 24 hours for cone snails), with sedation since the patient is conscious.
9. Sea urchin: remove spines, soak in hot water, and remove spines near joints surgically. Granulomas: intralesional triamcinolone 10 mg/mL, 0.1 mL a lesion, or excision.
10. Delayed infection with Mycobacterium marinum: clarithromycin 500 mg orally twice daily with ethambutol 15 mg/kg daily for 3 to 6 months.

Prevention: shuffle the feet in shallow water, wear footwear, and never handle shells or small octopuses. Follow-up at 1 week and 6 weeks.