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Jellyfish, Cnidaria Sting, Cnidaria, Cnidarian Venom, Nematocyst Sting, Portuguese Man-Of-War, Sea Nettle

  • See Also
  1. Marine Envenomation
  2. Neurotoxin
  3. Marine Injury
  • Background
  1. Invertebrates of phylum Cnidaria
    1. Inhabit shallow coastal waters
    2. Cnidaria includes (all have stinging nematocyst, anchor the skin and degranulate)
      1. Jellyfish
      2. Portuguese Man-Of-War
      3. Anemones
      4. Hydroids (fern-like fixed marine organism)
      5. Sea anemones
      6. Coral
        1. Responsible for more human cuts than Envenomation
        2. Often causes pruritic, red wheals at wound sites
        3. Remove debris and copiously irrigate with water
  2. Jellyfish (also called Sea Nettle) Anatomy
    1. Bell: Semi-transparent umbrella-shaped
      1. Varies in diameter from inches to 7 feet
    2. Tentacles
      1. As long as 100 feet in some cases
      2. Contain stinging namatocysts
  3. Portuguese Man-Of-War
    1. Bell: Purple air float (up to 12 cm in size)
      1. Float rides above surface of water
      2. Analogous to a sail, catching the wind to move
    2. Tentacles
      1. As with Jellyfish, contain nematocysts
      2. Tentacles may be several feet in length
  • Epidemiology
  1. Cnidaria responsible for most Marine Envenomations
  • Pathophysiology
  1. Nematocysts on tentacles responsible for stinging
  2. Nematocysts may sting even if tentacle detached
  • Symptoms (duration 2-3 days)
  1. Local burning pain
  2. Paresthesias
  3. Systemic symptoms occur in severe Envenomation
    1. Nausea or Vomiting
    2. Headache
    3. Myalgias
    4. Ataxia or Dizziness
  • Signs
  1. Local dermatitis
    1. Local erythema and edema
    2. Linear Papules
    3. Wheals
  2. Lesions resolve within hours
    1. Some lesions may necrose and Blister
  3. Severe systemic symptoms may occur
    1. Onset 5 minutes to hours after sting
    2. Observe for symptom rebound 6-8 hours after episode
  • Associated conditions
  1. Seabather's Eruption
    1. Pruritic dermatitis related to Cnidaria larvae
  • Management
  1. Avoid envenomated limb movement
  2. Rinse wounds wounds immediately with sea water (salt water, NOT fresh water)
  3. Apply 5% acetic acid or vinegar to area for 30 minutes
    1. Avoid Fresh water (will cause nematocyst discharge), Alcohol or urine
    2. Vinegar is contraindicated in Portuguese Man-Of-War stings (risk of venom release)
  4. Remove nematocysts and tentacles from skin
    1. Use credit card, shell or stick to scrape off
    2. Use gloves, or forceps
    3. Alternative method
      1. Apply shaving cream or Baking Soda slurry to area
      2. Use razor to scrape off nematocysts
    4. Do not rub or remove with towel
    5. Avoid compression
  5. After nematocysts and tentacles removal
    1. Shower in or soaking region in hot water for 20 minutes (inactivates venom)
  6. Other conservative measures
    1. Apply heat or cold to area
    2. Oral Analgesics and Antihistamines may relieve pain and Pruritus
    3. Avoid ineffective measures (meat tenderizer, ammonia, lemon)
    4. No data on Topical Corticosteroids
  • Course
  1. Symptom recurrence may happen within first month
  2. Fatalities are rare, but may occur if Anaphylaxis
  3. Stings with highest severity (most venomous)
    1. Australian Jellyfish
    2. Box Jellyfish (Hawaii)
      1. Antivenin (antivenom) is available and recommended
  • Prevention
  1. Wet suit use reduces risk of stings
  • References
  1. (2021) Presc Lett 28(7): 40
  2. Auerbach (2017) EM:Rap 17(10):6-7
  3. Habif (1996) Dermatology, p. 491
  4. Perkins (2004) Am Fam Physician 69(4): 885-90 [PubMed]