Allergic reactions to stinging insects are becoming more common. The number of hospitalisations and deaths from wasp, bee and hornet stings is rising.
What causes them?
An initial sting by a wasp or honeybee causes a person to become sensitised. It may take up to six weeks for someone to become fully reactive. This means their first sting may have no ill effects, but subsequent stings are likely to cause an allergic reaction.
An enzyme in sting venom provokes the allergic reaction. Wasps can inflict multiple stings, while a bee leaves its stinger in the skin and dies immediately.
What are the symptoms?
Most stings induce localised pain and swelling due to a toxic non-allergic reaction from the venom. The victim then recovers with no special treatment.
Mild allergic sting reactions present with redness and pain over a large area of skin. More generalised reactions with swelling, urticaria (hives) and redness spanning two joints may also occur.
In more severe reactions, there may be whole-body hives and swelling, with breathing difficulties, a 'feeling of dread' and generalised anaphylaxis with low blood pressure and shock.
Venom allergic reactions usually occur within ten minutes of the sting
Venom allergic reactions usually occur within ten minutes of the sting. Life-threatening reactions may occur in highly allergic individuals, older people and those with heart and respiratory diseases, especially if someone experiences multiple stings.
Stings on the face and neck may react worse than stings on a finger or toe. Bee keepers and gardeners are high-risk groups for bee sting anaphylaxis.
The longer the time between stings, the less likely it is a severe reaction will occur. Young children are more likely than adults to outgrow insect sting allergies.
What's the treatment?
Mild reactions require no more than antihistamine medication. More severe reactions and anaphylaxis require resuscitation with adrenaline by injection, antihistamines, steroids and intravenous fluids.
All wasp and bee allergic people should wear a MedicAlert bracelet and carry an adrenaline auto-injector.
Never exercise or take a hot bath after a sting as this may accentuate the reaction.
If someone you're with is stung and has an anaphylactic reaction, immediately call for help. If trained in resuscitation, maintain their airway and circulation and inject adrenaline, if available, into the thigh muscle.
How are they diagnosed?
Skin-prick testing using venom extracts, and specific venom RAST blood tests can be used to diagnose allergy to wasp and bee venom.
Unfortunately, these tests aren't as accurate as those for inhalant allergies. About ten per cent of people with a history of venom anaphylaxis have negative blood and skin tests.
Can venom allergies be prevented?
In summer, avoid areas frequented by wasps, particularly picnic sites, bins and areas where food is consumed outdoors. Don't drink sugary drinks outdoors and beware of wasps crawling into soft drink cans.
Never walk barefoot on grass in summer and don't wear bright clothes, which attract wasps.
If a bee or wasp approaches, don't panic or swat at the insect. Wait quietly for it to go away or walk away slowly.
Insect allergic people release a pheromone chemical odour from their skin, which seems to attract wasps and bees, so they tend to get stung repeatedly.
Wasp and bee venom desensitisation immunotherapy by injection is available and highly effective.
The injections are given over a five-year period and usually lead to complete resolution of the allergy with long-term protection. It should only be undertaken in specialist allergy clinics, as severe reactions are possible.