Allergic reactions are most frequently triggered by the stings of colony-building hymenopterans. They include bees, bumblebees, wasps, hornets and ants. In Europe, the Vespula genus is responsible for a large part of the allergic reactions. Unlike the wasps of the Dolichovespula genus, Vespula wasps are carnivores. As a result, they often come into contact with human populations – for example, people eating outdoors. In the US and South and Central America, fire ants are the cause of many of the reactions. European wood and garden ants only have a very small stinger, which is why their stings seldom lead to allergic reactions.
Insect stings can trigger local allergic reactions around the puncture site or reactions with symptoms that appear entirely elsewhere in the body, such as respiratory or circulatory problems. Doctors refer to this as a generalised or systemic reaction (see ‘Symptoms’ below). Researchers believe that 0.3 to 7.5% of the European population suffers from systemic allergic reactions to insect stings, depending on the region and occupation. Since the risk increases with the frequency of the stings, beekeepers are among those most often affected. According to data from the Anaphylaxis Registry, insect stings are one of the main triggers of anaphylactic shock in adults. Experts assume a prevalence of between 0.8 and 5% in Germany for systemic reactions. There are currently no precise figures for local reactions. Research has shown that local reactions occur more frequently than generalised reactions.
Insect Venom Allergy in Childhood and Adulthood
There are no precise figures on the prevalence in childhood. However, we do know that children under twelve have a lower risk than adults of recurring generalised reactions. Adults 40 years of age and over with other conditions such as cardiovascular disease or asthma have an increased risk of experiencing severe allergic reactions to insect stings. Patients who have already had a severe reaction to insect stings should speak to their doctor about the possibility of immunotherapy (see ‘Therapy’ below).
Allergic reactions to insect venoms are triggered by proteins in the venom. Twelve bee venom allergens, six wasp venom allergens, two bumblebee venom allergens and two hornet venom allergens have been identified so far. While bee stings occur mostly in the spring and summer, wasps are active in summer and autumn. Both species are frequently in contact with people – for example, on picnics or in flowering meadows. Hornet and bumblebee stings occur less frequently.
Risk factors for severe allergic reactions to insect venom:
- Increasing age (older than 40 years of age)
- Cardiovascular disease
- Allergic asthma
- Mastocytosis (a disease in which the body produces too many mast cells)
- A severe allergic reaction to an insect sting in the past
Insect stings can trigger the following reactions:
- Normal local reactions with no allergic immune response, with swelling to less than 10 cm in diameter. This swelling usually subsides within a few hours, while the itching at the puncture site can continue for several days
- Severe local allergic reactions with swelling to less than 10 cm in diameter. These reactions last longer than 24 hours, in some cases up to a week
- Severe systemic allergic reactions with nausea, vomiting, diarrhoea and, in rare cases, circulatory collapse
Non-allergic individuals can also experience severe reactions if they are stung by 50 to 100 insects at once (10 to 50 in children). With this many stings, a dangerous amount of venom enters the body, which can cause damage to the kidneys and liver. Stings in the facial area – the lips, for example – are more dangerous than stings on the legs or arms.
Diagnosis begins with a discussion during which the doctor asks the patient about the exact circumstances of the sting, any hereditary predisposition to allergies, and details about the reaction. It is important for the next phase of therapy to determine which insect triggered the allergic reaction and how high the risk is of (additional) severe reactions. The doctor therefore performs a skin and/or blood test in order to confirm whether the patient has been sensitised, i.e. whether he or she has developed specific antibodies following a previous sting. The results of these tests do not provide evidence of an allergy, but they reveal important information about allergic events in the body.
In patients with a high risk of anaphylaxis, skin tests are usually performed in hospital in order to minimise the risk of severe reactions to the test. A sting challenge test – the specific provocation of an insect sting – is only conducted on patients who have already successfully completed immunotherapy (for at least three to five years). It is carried out under strictly controlled conditions and only under medical supervision.
Specific immunotherapy (SIT) is available for patients with a severe insect venom allergy. Immunotherapy treats not only the symptoms but also the actual cause of the allergy (more information on allergy therapy here). If the immune system is stimulated with the insect venom allergen for a period of at least three to five years, 95% of people with a wasp venom allergy do not experience any reaction or only a very weak reaction when stung again. For people with a bee venom allergy, 80% of those treated have full protection; the remaining 20% generally have milder reactions than before. This protection does not last a lifetime in all patients. People at very high risk should therefore consider lifelong immunotherapy.
People at high risk of anaphylaxis must always carry an emergency kit with them containing an adrenaline auto-injector, a corticosteroid (in liquid or tablet form) and an antihistamine (in liquid or tablet form).
Prof. Dr. med. Dr. h.c. T. Zuberbier
Last changes made: July 2016