Stinging by jellyfish is caused by the simultaneous discharge of many thousands of microscopic stinging capsules called nematocysts. These are located on the surface of tentacles and in some species on the body of a jellyfish. Nematocysts contain coiled threads (tubules) loaded with venom. Upon contact, the nematocysts ‘discharge’ their tubules into the victim’s skin like mini harpoons. The more tentacles which make skin contact, the more venom is injected.
Stings cause immediate, sharp pain and an acute inflammatory skin reaction at the sting site consisting of redness, wheal and swelling which may progress to local skin destruction. Some stings cause rapid collapse. In Australia, life-threatening stings generally occur in tropical areas, with few in southern regions. Because of their smaller body size, children are at greater risk of the effects of envenomation.
Most stings are not serious and over-treatment of minor stings should be avoided. Wearing a full-body Lycra suit or equivalent provides good protection from stings.
Potentially fatal envenomation is caused by two jellyfish types in Australian Waters.
1. Box Jellyfish.
The Australian Box jellyfish, Chironex fleckeri, has a large (box-like) bell up to 20 x 30cm and multiple tentacles. It inhabits estuarine and onshore coastal waters. Contact with tentacles causes severe immediate pain and whip-like marks on the skin. A sting with several metres of tentacles can cause respiratory and cardiac arrest within a few minutes. Approximately 80 deaths have been recorded.
2. Jellyfish causing Irukandji syndrome
Approximately 10 small to medium-sized offshore and onshore jellyfish [including Carukia barnes and species of the Carybdea, Malo, Alatina, Gerongia and Morbakka genera] are known or suspected to produce an “Irukandji syndrome”. These jellyfish have only 4 tentacles and some are too small to be seen by the victim.
A minor sting on the skin with no tentacle visible, is followed in 5-40 minutes (typically 20-30) by severe generalised pain (often cramping in nature), nausea and vomiting, difficulty breathing, sweating, restlessness and a feeling of “impending doom”. Victims may develop heart failure, pulmonary oedema, and hypertensive stroke.
When a sting occurs, pieces of tentacles and non-discharged nematocysts may be left on the victim’s skin. In large or life-threatening stings, it is important to inhibit non-discharged nematocysts so that subsequent handling or treatment does not cause further envenomation.
Nematocysts from different species of jellyfish are either inhibited or stimulated to discharge by different substances used for first aid.
Vinegar (4-6% acetic acid) inhibits nematocyst discharge of Box jellyfish but does not provide pain relief from the venom already injected.
Although not proven to inhibit nematocyst discharge of all jellyfish causing Irukandji syndrome, its use is considered good first-aid practice.
Vinegar causes nematocyst discharge of some other jellyfish, including Bluebottle and is therefore recommended only for tropical areas where Box jellyfish and Irukandji stings occur.
Since it is usually difficult to recognise which species of jellyfish has caused a sting, management is based on the risk of serious stings in the known geographical distribution of dangerous species. Life- threatening stings primarily occur along the tropical coastline of Australia.
Tentacles on the skin
A variety of skin markings are associated with the stings of various jellyfish species and could include the following:
Symptoms and signs of severe stings
No one nationwide recommendation for first aid can be made because of the difference between jellyfish around Australia.
In most cases, first aiders are unlikely to be able to identify the specific jellyfish.
In the tropics, because of the risk that the victim has been stung by a potentially life-threatening jellyfish, your priority is to preserve life.
Outside the tropics, where huge numbers of non-life-threatening stings occur, the primary object is to relieve the victim’s pain by using heat or cold.
If pain persists or is generalised, if the sting area is large, or involves sensitive areas call an ambulance.