Jellyfish belong to the zoological phylum Cnidaria (or Coelenterata), which are hollow-bodied animals often equipped with stinging cells. Phylum Cnidaria contains the class Scyphozoa (true jellyfish) and the class Hydrozoa (of which the bluebottle, or Portuguese man-o’-war, is a member). For the purposes of this article, the term "jellyfish" will be used generally to refer to venomous marine animals from both classes Scyphozoa and Hydrozoa.
Several kinds of jellyfish have tentacles armed with millions of microscopic stinging devices called nematocysts, which inject toxins to paralyse or kill prey and to defend the jellyfish from potential predators. Even an invisible portion of jellyfish tentacle can have thousands of nematocysts, which are triggered by touch and certain chemicals. As a nematocyst is triggered and shoots out, it can activate adjacent nematocysts as well.
When you accidentally brush against a tentacle while swimming, (or, less commonly, stand on one while walking on the beach), the resulting sting can be irritating or painful, and may even be dangerous. The severity of the sting depends both on the species of jellyfish and the number of stings you receive. The nematocysts are located at intervals along the tentacles, so the greater the length of tentacle that makes contact with your skin, the greater the number of stings received.
The potency of the toxin varies greatly among the different kinds of jellyfish. Some jellyfish, such as those from the sea nettle, inflict stings that are merely annoying while others, like the Australian sea wasp Chironex fleckeri can kill a man in three minutes. Fortunately, none of the South African species are this lethal.
Symptoms and signs of jellyfish stings
Jellyfish stings may result in the following symptoms and signs:
- Burning discomfort or pain in the region of contact with the tentacle.
- Raised red lesions (papules) or welts in lines consistent with contact with the tentacle.
- The raised red lesions may develop into fluid-filled lesions or blisters (vesicles), and may heal with scarring and increased skin pigmentation.
- Most stings cause localised lesions only. Occasionally, however, especially with extensive or repeated exposures, an allergic reaction produces systemic symptoms (reactions elsewhere in the body, not only in the region of the sting). Systemic reactions may include: widespread itching, shortness of breath, nausea, vomiting, headache, dizziness, muscle weakness and spasms, irregular heart rate (arrhythmias), excessive tearing and runny nose, painful breathing (pleuritic chest pain), joint pain, stumbling gait.
In some people, jellyfish venom can produce a life-threatening allergic reaction, called anaphylactic shock, which requires emergency treatment. In anaphylactic shock, the affected person releases a large amount of a substance called histamine in response to a toxin or a substance to which they are allergic. This results in swelling of the body tissues, constriction of the small airways in the lungs, collapse of the blood circulation, heart failure and sometimes death.
Treatment of jellyfish stings
Treatment consists of preventing further envenomation (stinging), pain relief and management of any complications.
If someone gets stung, take the following steps as quickly as possible:
- Rinse the affected area of skin with sea water to wash away adherent nematocysts, immediately before attempting to remove the tentacles. Tentacles that are disturbed may release additional nematocysts, causing further irritation. The nematocysts can continue to sting and deliver toxin, even if the jellyfish is dead or only a piece of tentacle is present. Do not rinse with fresh water because this can cause the nematocysts to swell and discharge. Also avoid household ammonia. Don't rub the area as this can also activate the nematocysts.
- While continuing to rinse, gently remove any adherent tentacles. Lift the tentacles off the skin - rubbing or dragging them off can cause further stinging. Protect your hands from getting stung by using gloves, tweezers, a stick or some other object to remove the tentacles. Remember not to rub your eyes if you've just handled the tentacles.
- The nematocysts can be deactivated with various common substances such as vinegar and meat tenderiser. The mild acid in vinegar (or dilute acetic acid 5-10%) "fixes" or deactivates the nematocysts so they will not be triggered and release toxin.
Meat tenderiser is another excellent source of relief from stings. It should be applied as a paste mixed with a little water to the affected area of skin. The meat tenderizer contains papain, an enzyme from papaya or pineapple that breaks down the proteins of the jellyfish toxin and destroys it. This should provide relief from the stinging within 15 minutes.
Alcohol (including methylated spirits or liquor) and even human urine are other substances that can be used to deactivate nematocysts.
Another method to remove any remaining nematocysts is to dust the affected area of skin with baking-powder (sodium bicarbonate) or talc. Powders help stabilise the nematocyst by drying the cells out. You can also try spraying the skin with shaving cream to coat the area. The nematocysts will stick to the cream, which you can then carefully scrape off with the dull edge of a butter knife.
- Pain from jellyfish stings can be treated with topical anaesthetics (applied at the site of the sting) such as lidocaine and benzocaine, which are sometimes found in sunburn preparations. A small percentage of people are allergic to these ingredients, however. Also try immersing the affected part in water as hot as can be tolerated for 30 minutes to aid destruction of the toxin, with a pinch of Epsom salts or table salt to prevent any nematocysts from being triggered. Some authorities claim that applying ice packs for about 10-15 minutes can provide relief.
Pain may sometimes be severe enough to warrant treatment with morphine in adults or pethidine in children.
- If you have received multiple stings but are not in anaphylactic shock, the non-prescription antihistamine Benadryl, taken orally, may reduce some of the body's reactions. Benadryl cream, aloe gel or witch hazel applied topically may also provide some relief from inflammation or itchiness, as will topical hydrocortisone cream.
Oral antihistamines and corticosteroids are used to treat more serious allergic reactions. Anaphylactic shock may also be treated with adrenaline, and artificial respiration.
Your doctor may administer intravenous calcium gluconate to relieve muscular cramps.
Secondary bacterial infection at the site of the sting may occur, especially if vesicles form, for which your doctor will prescribe antibiotics.
What is the outcome of jellyfish stings?
Most jellyfish stings resolve spontaneously or require only minor forms of treatment, and do not cause lasting damage. Systemic symptoms usually abate within a few hours. However, stings can occasionally be life-threatening, particularly for children and the elderly. Severe anaphylactic (allergic) reactions causing cardiovascular, respiratory and renal failure are rare but the risk intensifies with repeated exposures to the venom, especially in people who are atopic (prone to allergic responses).
Skin reactions may recur one to two weeks later and may require further local treatment.
Can jellyfish stings be prevented?
Lightweight protective clothing, such as a wetsuit or a layer of petroleum jelly spread on bare skin can help protect you against stings when swimming.
Before venturing into the water, check with other swimmers or lifeguards to find out if jellyfish are a problem in a particular area or season.
When to call the doctor
Seek medical attention if you have been stung by a jellyfish and:
- You begin to develop persistent muscle spasms
- Secondary bacterial infection develops
- You have difficulty breathing, or show any other signs that you may be going into anaphylactic shock. Seek emergency medical attention.
(Reviewed by Prof Don du Toit)