Bee and Wasp Envenomation

Stings by Hymenoptera (honeybees, bumblebees, wasps, yellow jackets and hornets) cause local pain in nearly everyone and systemic allergic reactions in about 3% of adults and 1% of children. They kill more people in many regions than snakes and spiders combined.

Honeybee venom contains melittin, phospholipase A2, hyaluronidase and apamin. Wasp venom contains antigen 5 and phospholipase A1. A honeybee leaves its barbed stinger and venom sac in the skin, and the sac continues to pump venom for 20 to 60 seconds. Wasps and hornets can sting repeatedly.

Reaction patterns

• Normal local: pain, wheal and redness lasting hours
• Large local: swelling over 10 cm lasting over 24 hours, up to 7 to 10 days
• Anaphylaxis: usually within 30 minutes
• Toxic reaction after mass stings: over 50 stings, with a dose of about 20 stings/kg potentially lethal (500 or more in an adult)
• Delayed reactions: serum sickness and neuritis

Risk factors for severe reactions: mastocytosis and raised baseline tryptase, beta blockers, ACE inhibitors, cardiovascular disease and previous systemic reactions. Complications: anaphylactic shock, rhabdomyolysis, intravascular hemolysis, acute kidney injury, hepatic injury, myocardial infarction (Kounis syndrome) and eye injury.

• Immediate sharp burning pain with a central punctum, wheal and erythema
• Large local reactions: expanding swelling over 1 to 2 days, itch and sometimes lymphangitis
• Anaphylaxis: urticaria, angioedema, wheeze, stridor, vomiting, hypotension and collapse
• Mass envenomation: nausea, vomiting, diarrhea, headache, fever, hypotension, then dark urine, jaundice and oliguria at 24 to 72 hours
• Red flags: stings in the mouth or throat, airway swelling, hypotension, many stings, and dark urine

1. Clinical diagnosis from the sting and the time course.
2. Anaphylaxis: serum tryptase at 1 to 2 hours after onset and a baseline value later (a rise over 20% plus 2 ng/mL above baseline supports the diagnosis).
3. Mass stings: creatine kinase, creatinine, urea, electrolytes, LDH, bilirubin, liver tests, urine for myoglobin and hemoglobin, ECG and troponin.
4. Allergy testing at 4 to 6 weeks: venom-specific IgE, skin prick and intradermal tests, and baseline tryptase to detect mastocytosis.

Differentials: other insect bites, cellulitis, contact dermatitis, anaphylaxis of other cause.

1. Remove the stinger immediately by scraping or pulling. Speed matters more than technique. Wash, apply ice and elevate. Remove rings.
2. Local reactions: paracetamol 1 g orally every 6 hours, ibuprofen 400 mg orally every 8 hours with food for 2 to 3 days, cetirizine 10 mg orally daily, and hydrocortisone 1% cream twice daily.
3. Large local reactions: prednisolone 40 mg orally daily for 3 to 5 days (children 1 mg/kg), and cefalexin 500 mg orally every 6 hours for 5 to 7 days only if infection is evident.
4. Anaphylaxis:
   • Epinephrine 0.5 mg IM (0.5 mL of 1:1000) into the anterolateral thigh (children 0.01 mg/kg, maximum 0.5 mg), repeated every 5 minutes as needed.
   • IV crystalloid 20 mL/kg, oxygen, and salbutamol 5 mg nebulized for wheeze.
   • Chlorphenamine 10 mg IV slowly (children 0.2 mg/kg) and hydrocortisone 200 mg IV (children 4 mg/kg).
   • Refractory shock: epinephrine infusion 0.05 to 0.1 micrograms/kg/min. In patients on beta blockers, glucagon 1 to 5 mg IV over 5 minutes.
   • Observe for 6 to 12 hours (up to 24 hours for severe cases).
5. Mass envenomation: IV crystalloid at 200 to 300 mL/h to keep urine output over 1 mL/kg/h, transfusion for hemolysis, haemodialysis for kidney failure and monitoring for 72 hours.
6. Venom immunotherapy for patients with systemic reactions (and selected adults with skin-only reactions or raised tryptase): build-up then maintenance of 100 micrograms of venom every 4 weeks for 3 to 5 years. It is protective in about 90% for wasp venom and 75 to 85% for honeybee venom.
7. Adrenaline auto-injector: 0.3 mg IM for patients over 30 kg (0.15 mg for 15 to 30 kg), two devices, with training. Avoid beta blockers and ACE inhibitors where possible.

Counsel on avoiding perfumes and bright clothing, covering food and drink outdoors, and having nests removed by professionals.