Insect Venom Allergy: A Short Review

Author: V. Dimov, M.D., Fellow, Creighton University Division of Allergy & Immunology
Reviewer: S. Randhawa, M.D., Fellow, LSU (Shreveport) Department of Allergy & Immunology

There are over 50 reported deaths per year due to insect stings in the U.S. The most common stinging insects are bees and wasps. They can cause severe allergic reactions including anaphylaxis and anaphylactic shock. Reactions to wasp stings are more common than those to bees.


Figure 1. Mind map of insect venom allergy.

Classification

Bee and wasp venoms are different. Both contain hyaluronidase but differ in the content of other allergens. Patients allergic to wasp are rarely allergic to bee.

Sensitization

People are rarely stung by wasps -- once every 10-15 years. Sensitization to wasp venom can occur after a single sting. In contrast, allergy to bee venom occurs after frequent stings by bees. Consequently, most people allergic to bees are beekeepers or neighbors of beekeepers.

IgE antibodies to Hymenoptera venom are present in 20-30% of adults who had an insect sting in the previous 2-3 years.

Reaction to Wasp	Reaction to Bee
More common	Rarer
After a single sting	After many stings
Typical narrow waist and little hair	Hairy "fuzzy" bee

Table 1. Comparison of allergic reactions to wasp and bee venom.


Figure 2. A yellow jacket wasp with a typical narrow waist (left) and a honey bee with a fat hairy "fuzzy" body (right). Image source: Wikipedia 1, 2, GNU Free Documentation License.

Honeybees only sting once -- when they sting, their stinger comes out and they die. Wasps can sting multiple times, they can be aggressive and chase their victims. Other stinging insects are hornets and fire ants.

Clinical features

Normal reaction: pain, erythema, a small area of edema (less than to 1 cm diameter).

Allergic reactions can be:
- local
- generalized

Local reactions

Edema can affect a hand/foot or even an entire limb, it can lead to blistering. Symptoms begin within 15 to 30 minutes and arise distant from the site of sting. Not dangerous unless it affects the airway.

Large local reactions are usually late-phase IgE-mediated, with large severe swelling (8-10 inches in diameter) developing over 24 to 48 hours and resolving in 2-7 days.

Generalized (systemic) reactions

Systemic allergic reactions occur in 1% of children and 3% of adults. Children generally have a more benign course after insect stings because they usually have only cutaneous systemic reactions. Remember:

C
Children
Cutaneous only

A
Adults
Airway
Anaphylaxis

Systemic reactions often start with erythema and pruritus, followed by urticaria and facial or generalized angiooedema.

Patients often feel extremely ill, as if they are going to die ("a sense of impending doom"). SOB can occur due to laryngeal edema or bronchospasm. In severe reactions, hypotension leads to lightheadedness and loss of consciousness. Less common features: abdominal pain, incontinence, chest pain, blurry vision.

The onset of generalized reactions is usually within 10 minutes of a sting.

Diagnosis

- History
- Venom-specific IgE antibodies

Many patients say the sting was from a bee when it is was from an wasp. Vast majority of patients (except beekeepers) will be wasp allergic.

History should be confirmed by demonstrating specific IgE against wasp or bee venom. This is done first by skin test (prick or intradermal) and/or second by blood test (RAST).

Skin tests are positive in 65-80% of patients with a history of systemic allergic reactions to insect stings. RAST is less sensitive than venom skin tests and can lead to false positives.

Remember:
Allergy = clinical reactivity
Sensitization = specific IgE antibodies, can occur without clinical reactivity (allergy)

Patients are rarely allergic to both bee and wasp venom.

Acute management

Drugs: EASI

Epinephrine IM
Antihistamines PO, IM
Steroids PO, IM, IV
Inhaled b2-agonists, if wheezing

Treatment of choice is epinephrine with a 1:1,000 (1 mg per mL) aqueous solution. Adult dose is 0.3 mL, children dose is 0.01 mg per kg (maximum: 0.3 mL, i.e. one adult dose). Dose can be repeated every 10-15 minutes, up to 2-3 times but in practice repeat administration is generally avoided since high doses of epinephrine can induce arrhythmias.

Patients taking beta blockers can be relatively resistant to epinephrine effect.

Further management

- Desensitization (immunotherapy)
- Self medication with EpiPen

Desensitization (immunotherapy)

Immunotherapy causes a switch from the abnormal Th2 cytokine response to a Th1 response.

Venom immunotherapy has a 98% efficacy but carries a 10% risk systemic allergic reaction and can cause anaphylaxis.

Initial course of weekly injections over 3 months (12 weeks), reaching the highest dose of 100 mcg (equivalent to two stings). Then, maintenance injections of 100 mcg monthly for 5 years. Patients are observed for 30-60 minutes after each injection.

The maintenance dose is 100 mcg for each venom to which the patient has a positive skin test. Mixed vespid venoms (total dose of 300 mcg) are most commonly used.

It is easier to remember that patients come to the office once a week for 12 weeks for their injections. At the end of the 12 weeks, they have been desensitized to the bee stings. Then, they come once a month, for a minimum of five years. Some high-risk patients should be treated indefinitely.

The incidence of systemic reactions with insect venom immunotherapy (10-15%) is similar to inhalant allergen immunotherapy. Less than 50% of reactions require epinephrine injection.

Up to 50% of patients experience large local reactions. Such local reactions are not associated with an increased risk of systemic reactions to subsequent injections.

Self medication

- Oral antihistamines to take as soon as patient is stung
- Syringes preloaded with epinephrine (EpiPen TM)

Epinephrine auto-injector comes in 2 forms: EpiPen, 0.3 mg and EpiPen Jr., 0.15 mg.

EpiPen delivers epinephrine within seconds to minutes and "buys" the victim 20 minutes to get to the nearest emergency room. Some patients will have delayed reactions to the insect venom and this is the reason why they still have to go to the ER to be observed for 3-6 hours.

EpiPens expire every 18 months and it is recommended to have 2 of them handy.

References

Clinical review: ABC of allergies, Venom allergy. Pamela W Ewan. BMJ 1998;316:1365-1368.
Stinging Insect Allergy. David B. K. Golden. American Family Physician, June 15, 2003.
Patient information. Tips to Remember: Stinging insect allergy. AAAAI.org.
Anaphylaxis to stings and bites. Robert J Heddle. MJA 2006; 185 (5): 290.

Related reading

'Tongue Drops' Cut Bee Sting Allergy. WebMD, 03/2008.
Fire Ant Stings. Consultant, Vol. 46, No. 13, November 2006.

Videos


Bee Sting Allergies Explained by Robert M. Overholt, M.D.

Published: 08/24/2007
Updated: 04/09/2009