Wasp Venom Allergy

Wasp venom allergy is an IgE-mediated allergy to the venom of vespids: wasps (Vespula), yellow jackets, hornets (Vespa) and paper wasps (Polistes). It is the commonest venom allergy in many regions, and stings often occur in late summer.

Pathophysiology. Major allergens are antigen 5 (Ves v 5), phospholipase A1 (Ves v 1) and hyaluronidase (Ves v 2). Cross-reactivity between Vespula species and hornets is high, and with Polistes it is variable.

Wasps can sting repeatedly because the stinger is not barbed. They are attracted to sweet food, drinks and rubbish.

Mastocytosis and raised baseline tryptase carry a high risk of severe, even fatal, reactions after wasp stings.

• Large local swelling, pain and redness
• Generalised urticaria, flushing and angio oedema
• Wheeze, stridor, hypotension and collapse
• Vomiting and abdominal cramps
• Reaction within minutes, often during outdoor meals
• Repeated stings in a single event, in some

• History: insect, circumstances, time to onset, and features. Identification of the insect is often poor, so tests are needed.
• Skin prick and intradermal test with wasp (Vespula), hornet and honeybee venom, and specific IgE to wasp venom and Ves v 5 and Ves v 1: Ves v 5 positivity indicates wasp sensitisation. Double positivity with honeybee venom may be caused by cross-reactive carbohydrates, so component testing and basophil activation testing help to find the true cause.
• Baseline tryptase: raised values suggest mast cell disease.

Differential diagnosis.

• Honeybee or bumblebee venom allergy
• Large local reaction without systemic risk
• Idiopathic anaphylaxis
• Systemic mastocytosis
• Toxic reaction to multiple stings
• Cellulitis at the sting site

• Immediate care after a sting: cool the site, and give an oral antihistamine for local symptoms: cetirizine 10 mg in adults (children 1 to 5 years 2.5 mg twice daily; 6 to 11 years 5 mg twice daily). Large local reactions may need oral prednisolone 40 mg daily for 3 days in adults.
• Anaphylaxis: adrenaline 0.5 mg intramuscularly (children 0.01 mg/kg, maximum 0.5 mg) into the anterolateral thigh, repeated after 5 minutes if no improvement, plus oxygen and intravenous fluids, and observation for at least 6 hours.
• Adrenaline auto injector: 150 microgram for 7.5 to 25 kg, 300 microgram for 25 to 50 kg, 500 microgram for over 50 kg, with a written action plan and training.
• Wasp venom immunotherapy for systemic reactions beyond skin signs and a positive test: build up then maintenance of 100 microgram of venom every 4 weeks (200 microgram if reactions continue), for 3 to 5 years, and lifelong for patients with mastocytosis or a very severe reaction. It protects more than 95% of patients.
• Sting avoidance: cover food and drink outdoors, check cans before drinking, avoid perfume, wear shoes, and have nests removed professionally.
• Review drugs: beta blockers and angiotensin converting enzyme inhibitors.

Special groups.

• Patients with mastocytosis or high baseline tryptase: lifelong therapy, and a cautious build up in hospital.
• Children: the risk of future systemic reaction is lower if reactions are confined to skin, so immunotherapy is not always needed.

Monitoring. Review every 6 months during build up and yearly in maintenance. Check auto injector dose and expiry. Baseline tryptase yearly.

Referral and escalation. Refer to allergy for any systemic reaction to a wasp or hornet sting. Emergency for anaphylaxis.