During the summer months insects of the order Hymenoptera which include the Yellow Jacket Wasps (Vespula germanica), HoneyBee (Apis mellifera) and Paper wasp (Polistes annularis) may sting unsuspecting people.
by Dr. Adrian Morris
If allergic to the stinging insect’s venom, these people might develop an allergic reaction, which may range from mild to life threatening. Reactions to subsequent stings range from being the same in 43%, reduced intensity in 45% and more severe in only 12%. In fact a many people (50% adults and 80% children) with mild reactions will lose their insect venom allergy over time. On average four Bee or Wasp sting anaphylaxis deaths are reported per year in the UK and the average age being 50 years (BSACI). Bee venom allergic reactions run a greater risk of life-threatening anaphylaxis than do wasp venom allergic reactions. Remember that you are statistically more likely to die from being murdered, or killed in a Road Traffic Accident rushing to hospital than from the actual sting itself. Fire Ant allergy and anaphylaxis occurs in the USA but not in the UK.
The most allergy provoking protein in a wasp sting venom is an enzyme called Phospholipase A1 and Hyaluronidase, whilst Hyaluronidase and an enzyme called Acid Phosphatase are the major allergy provoking components of Bee venom. Sensitisation to insect venom can occur after a single sting. Other enzymes in insect venom called hyaluronidases may result in occasional cross-reaction allergy, but the vast majority of people are allergic to either wasp or bee but not both.
Wasps and Bees are social insects and rarely attack people, but tend to sting if disturbed. In the UK, the vast majority of insect sting allergic reactions are due to wasps. Bee sting allergy tends to occur in high-risk groups such as beekeepers, gardeners and farmers. Once stung the identifying feature of a bee sting is the stinger left behind in the skin, a wasp does not do this. The female honeybee carries the stinger and dies shortly after discharging a sting.
Diagnosis of Wasp and Bee Venom Allergy
We usually test for Wasp and Bee venom allergy using the ImmunoCAP RAST blood test that measures specific Venom IgE antibodies in the blood. The test has certain drawbacks in that it is difficult to predict severity of future reactions from the blood test. High levels of venom specific IgE ( Honey bee ImmunoCAP i1 or Wasp venom ImmunoCAP i3) do not necessarily predict a severe reaction. For potential wasp or bee sting venom anaphylaxis there are newer more specific IgE component allergen tests that are predictive of a significant clinical reaction. For wasp venom this is Ves v 5 (ImmunoCAP i209) and for bee venom allergy, the specific IgE antibody is Api m1 (ImmunoCAP i208) and these are good markers for a serious venom allergic reactions or even anaphylaxis. Both these tests are also useful for identifying people who will benefit from sting desensitisation by injection immunotherapy. Occasionally venom allergic people have negative RAST tests – possibly due to their reacting to another protein component of the venom or the test being done too soon after the sting (we therefore recommend that the test is done 6 weeks after a sting to make sure the IgE antibody levels have returned to normal). Skin Prick Tests and Intraderma testing are more accurate for the diagnosis of clinical insect venom allergy, but do carry a small risk of inducing a severe allergic reaction as traces of the venom are applied to the skin during testing. 10% of patients who experience wasp anaphylaxis will have negative allergy tests – possibly due to the IgE being tissue bound or there being a non-IgE mechanism. Hence a negative allergy test does not absolutely exclude sting anaphylaxis. Patients with severe insect venom reactions should also have a baseline blood test for Tryptase (an enzyme released by Mast cells during anaphylaxis but also present in a rare condition called Systemic Mastocytosis).
We do get asked to test children and adults for bee and wasp venom allergy when they have never been stung before. One can only develop a venom allergy after a sting (sensitising dose). The reaction to a subsequent sting may suggest an allergy has developed and at this point allergy testing would be appropriate.
Features of sting allergy
Normally some pain redness and swelling accompanies a sting, this is not an allergy but rather a local toxic reaction to the venom. This non-allergic reaction develops over a period of a few hours with no adverse consequences and settles over a day or two.
An insect venom allergic individual will have a more immediate and severe reaction. This may range from a mild reaction with redness and swelling spanning two joints, intense itching and pain all occurring within minutes of the sting. More severe reactions include generalised swelling and itching (scalp, palms & soles of feet), urticaria and angioedema, faintness, sweating, a pounding headache, stomach cramps and vomiting, a feeling of “impending doom”, a tight chest or choking sensation with swelling of the throat and in extreme cases, anaphylactic shock with death ensuing.
This may develop within 10 minutes of a sting, so early intervention is essential. There is no predicting whether future stings will result in more or less severe allergic reactions or anaphylaxis. However, if a long time has lapsed since last stung, the reaction is likely to be less severe.
Mild reactions require no more than a double dose of oral antihistamine such as 8mg Chlorpheniramine (Piriton) in older children and adults. More severe and generalised reactions in adults require immediate intra-muscular antihistamine administration (Chlorpheniramine 10mg), use of a B agonist asthma inhaler (Salbutamol) and oral corticosteroids (Prednisilone 30mg). Severe reactions with shock and respiratory difficulties require immediate intra-muscular adrenaline (1:1000) 0.5ml administration in adults (Epipen, Emerade and Jext pen), as well as intra-muscular Chlorpheniramine 10mg and intra-muscular Hydrocortisone 200mg.
Adult patients find using a pre-loaded adrenaline syringe (Jext, Emerade or Epipen 300ug) very convenient in emergencies. They should have the dose repeated after 5 minutes if there is no satisfactory response. In children under 5 years of age, we give 0.1 to 0.3 ml of adrenaline (1:1000) depending on age and an Jext or Epipen Junior conveniently dispenses 150ug of adrenaline per dose. The patient should still immediately be taken to A&E after the adrenaline administration, for further assessment and monitoring. Measurement of Tryptase in the blood will also confirm that an allergic reaction has taken place.
Wasp and Bee avoidance measures
People who are known to be allergic to wasps and bees should try wherever possible to avoid being stung and stay away from areas frequented by bees and wasps. If a wasp or bee approaches, remain calm and still, do not try to swat the insect as this may frighten it. If it lands on you, gently blow it off your skin. Certain people seem to attract bees and wasps and we suspect that they secrete a chemical Pheromone in the skin, which heightens the insect’s agitation.
Insects are drawn to flower fragrances and bright colours with dark backgrounds. Therefore white clothing is safest for insect allergic people to wear. Avoid perfumes, uncovered cold drinks, fruit juices, sugary foods outdoors as these attract insects. Wasps also tend to creep into soda cans and other beverages. Never walk on grass barefoot and avoid orchards in blossom. Carefully shake out clothing left on the ground. Avoid mowing lawns, trimming hedges or pruning trees. Keep dustbins and food well covered. Bees and wasps tend to frequent clover fields, picnic areas and soiled dustbins in particular. If one comes across a bee hive or wasps nest in the garden, do not disturb it. Rather seek help in having it removed. A few Cloves stuck into an Orange, which is placed on the picnic table tend to discourage bees and wasps from causing a nuisance at picnics.
If stung by a bee, immediately scratch or flick off the barbed stinger (don’t squeeze more venom into the skin). Apply ice or a cold compress to the sting, in a mild reaction a freshly cut onion will soothe the skin if applied to the sting area for 20 minutes. Life threatening reactions are more likely to occur in highly allergic individuals, elderly people with pre-existing cardiac or respiratory diseases or in multiple stings. Stings to the face, neck and scalp or more likely to trigger anaphylaxis. Do not exercise or have a hot bath after a sting as this may increase the venom distribution.
Patients prone to severe reactions should carry emergency medication on them and this includes an Epipen, Emerade or Jext Adrenaline injector, Antihistamine medication and Prednisilone. We usually recommend the patient have 2 Epipens, one at home and the other in the workplace or school. All wasp and bee allergic people should have a Medic Alert bracelet carrying details of their allergy.
Venom Desensitisation Immunotherapy (VIT) is a highly successful means of treating people with severe generalised venom allergic reactions. Venom immunotherapy is 95% effective in reversing and “curing” wasp venom allergy and 80% effective for bee venom allergy. This is particularly useful for Beekeepers, Horticulturists, Gardeners and Farmers who find it difficult to avoid stinging insects. Children are less likely to have as severe allergic reactions as adults, and have a better prognosis. Venom Immunotherapy should therefore only be considered in children who have had severe sting-induced systemic allergic reactions (anaphylaxis). VIT must not be undertaken in the abscence of demonstable venom-specific IgE. These injections are carried out at weekly intervals during the initial treatment phase and then monthly for a further 3 years during the maintenance phase (BSACI Guidelines). By the end of the treatment, the patient is able to tolerate 100ug of venom, the equivalent of two bee or wasp stings, with no adverse reaction. Results are excellent, but Immunotherapy does run the risk of inducing an allergic reaction. The ALK Abello Wasp and Bee venom vaccines are extremely safe to use. Injection Immunotherapy should only be performed in specialist hospital-based clinics with readily available resuscitation equipment and the patient should be observed for one hour after each injection.
Reference: Krishna MT, Ewan PW, Diwakar L, Durham S, Frew AJ, Leech SC and Nasser SM. Diagnosis and management of hymenoptera venom allergy:British Society for Allergy and Clinical Immunology (BSACI) guidelines. Clinical and Experimental Allergy 2011:41;1201-1220