1. 27
Allergy to Insect Stings
By SusanWaserman, MD, FRCP; and
Abdullah Aburiziza, MD, XXX
S
tinging insects which cause IgE-mediated reactions belong to the order
Hymenoptera. There are four families within that order, and including
ent Vespidae (yellow jackets, hornets and paper wasps), Apidae (bees), Halic-
pla cem tidae (sweatbees) and Formicidae (ants). Two families, the Vespidae and the
fo r
Ju s t Apidae are associated with most stinging insect allergy.
Hymenoptera venom anaphylaxis has been associated with about 40 deaths
per year in the U.S., yellow jackets the most common cause in North America.1
Asymptomatic venom sensitization is common in adults but transient, and
can disappear at a rate of 12% per year.2
Fatalities are less common in children than adults.3 Approximately one half
of fatal reactions occur in individuals with no previous history of allergic re-
actions to stings.4 Though patients with atopy have an increased risk of be-
coming sensitized, they do not seem to develop systemic reactions more
Dr. Waserman is an Associate frequently than non atopics.5
Professor of Medicine and the This article reviews the clinical features of stinging-insect allergy, as well as
Training Program Director for diagnosis and treatment, including avoidance, injectable epinephrine, and
Allergy and Clinical Immunology venom immunotherapy.
at McMaster University, Hamilton,
Ontario. Classification of Reactions
Reactions from insect stings are classified as local (normal or large local) or sys-
temic (allergic and non-allergic). Local reactions are limited to the area con-
tiguous with the sting site. Large local reactions are also contiguous but are
Dr. Aburiziza is an defined as being 10 cm in diameter or larger and lasting longer than 24 hours.6
xxxxxxxxxxxxxxxxxxxxxxxxxxxxx Frequently, these are misdiagnosed as cellulitis and treated with antibiotics.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxx Local reactions are not IgE-mediated, hence venom skin testing and im-
xxxxxxxxxxxxxxxxxxxxxxxxxxxxx munotherapy are not indicated, however large locals may be and should be
evaluated by an allergist.
Systemic allergic reactions occur at sites distant to the sting and affect 0.4%
to 0.8% of children and 3% of adults.1 These are IgE-mediated. Symptoms
range from mild (cutaneous manifestations) to severe, with symptoms such as
laryngeal edema, bronchospasm, and hypotension. Non-allergic systemic re-
actions are less common and are not IgE-mediated. These include nephrotic
syndrome, serum sickness, neurologic manifestations (Guillain Barre), rhab-
domyolysis, and hemolysis.7
Allergy&Asthma
2. 28 Allergy to Insect Stings
A positive skin or RAST (radioallergosorbent A positive skin or radioallergosorbent test
(RAST), a blood test which measures IgE to each of
test), a blood test which measures IgE to each the venoms, in conjunction with a systemic reac-
of the venoms, in conjunction with a systemic tion is diagnostic of venom allergy. In the weeks
after a sting reaction, some patients have negative
reaction is diagnostic of venom allergy.
skin tests attributable to a refractory period. They
should have repeat skin testing after four to six
Diagnosis weeks. Patients with a negative skin test and a his-
Recognition of anaphylaxis is often difficult, es- tory of anaphylaxis should have a RAST. If results
pecially with the first sting and if urticaria are ab- are still negative, skin tests should be repeated
sent. Vasovagal responses may be confused with after three to six months.8
anaphylaxis, however these are usually accompa-
nied by bradycardia and anaphylaxis with com- Treatment
pensatory tachycardia. An elevated serum Acute Therapy. Avoidance of stinging insects is
tryptase, a mast-cell-specific enzyme, provides ad- important. Patients are advised to destroy nests,
ditional evidence for anaphylaxis, but it is not wear shoes, avoid perfumes outdoors, cover
very sensitive. garbage receptacles and use insecticides. Treat-
Insect identification is also difficult, however ment of local reactions includes icing, elevation,
certain factors may be helpful. Honeybees leave a analgesics, and antihistamines.
stinger behind, whereas vespids do not. Yellow For acute systemic reactions, epinephrine
jackets tend to be aggressive, and will sting if un- 1:1,000 solution, given as 0.01 ml/kg (maximum
provoked. They are found around food and dose 0.3 ml/kg) is injected intramuscularly. All pa-
garbage cans. Since they nest in the ground peo- tients with insect-sting anaphylaxis should carry
ple are often stung while mowing the lawn. Hor- an epinephrine autoinjector, prescribed according
nets are also aggressive and are found in nests, to weight. A “junior” dose of 0.15 mg of epi-
trees and shrubs. nephrine is for patients weighing 15 kg to 30 kg
Skin testing to the five Hymenoptera standard- and the regular dose of 0.30 mg of epinephrine is
ized venoms is the standard method of diagnosis. for patients weighing greater than 30 kg. Patients
Skin-prick tests to venoms, if negative, are fol- should be taught to self inject if necessary after a
sting. The dose can be repeated in five to 10 min-
utes if symptoms persist and patients should be
Systemic allergic reactions occur at sites distant instructed to call 911. An antihistamine can be
to the sting and affect 0.4% to 0.8% of chil- given, but is second-line therapy, and its use
should not delay the administration of epineph-
dren and 3% of adults.1 rine. Corticosteroids have no proven benefit in
the acute period but may be useful in treating the
lowed by intradermal skin tests. Intradermal con- late-phase manifestations of anaphylaxis.
centrations start at 0.001 µg/ml to 0.01 µg/ml and Referral to an allergist is extremely important
increase 10 fold to a maximum of 1 µg/ml. Skin for diagnostic skin testing, patient education, and
tests are indicated when immunotherapy is being venom immunotherapy.
considered, namely for individuals who have had Immunotherapy. Venom-specific immunother-
a systemic allergic reaction. For children aged two apy is the treatment of choice for stinging-insect
to 16 years who have had only cutaneous reac- allergy. It is safe and highly effective for prevent-
tions, immunotherapy is not given since most ing future reactions. Immunotherapy is 97% to
(90%) will not experience more severe or progres- 100% effective in preventing systemic reac-
sive symptoms with their next sting (Table 1). tions,9whereas reactions in untreated individuals
Allergy&Asthma
3. 29
Table 1
Selection of Patients for Immunotherapy
Reaction to sting Result of skin test or RAST Venom
immunotherapy?
Child
Systemic, non-life-threatening,
immediate, generalized urticaria,
angiodema, erythema, pruritus + or − No
Systemic, life-threatening, possible
cutaneous symptoms, but also
respiratory symptoms (laryngeal edema
or bronchospasm) or cardiovascular
symptoms (hypotension, shock) + Yes
Adult
Systemic + Yes
Systemic − No
Child/Adult
Large local (> 2 inches, > 24 hour
duration) + or − No
Normal (< 2 inches, < 24 hour
duration) + or − No
is as high as 60%. temic reaction. About 3% to 12% of patients
The venoms used for immunotherapy are the have treatment-induced systemic reactions that
same as those used for skin testing (honeybee, yel- generally are mild and occur in the early phases of
low jacket, yellow hornet, white-faced hornet, immunotherapy. If a systemic reaction occurs,
wasp, and fire ant, if applicable). The routine reg- one half of the dose is given the next week. This
imen begins with an injection of 0.01 µg and ad- approach, however, is individualized to the pa-
vances weekly to 100 µg (equivalent to two
stings). The maintenance dose of 100 µg is given
Avoidance of stinging insects is important.
every four weeks for a year, and then every six to
eight weeks. Venom selection is based mainly on Patients are advised to destroy nests, wear shoes,
skin-test results, clinical history and a pattern of avoid perfumes outdoors, cover garbage
venom cross-reactivity. One recommendation is
that immunotherapy includes all venoms giving a
receptacles and use insecticides.
positive skin test. However there is allergenic
cross-reactivity of the four vespid venoms, hence tient. Pretreatment with antihistamines were
most patients with multiple sensitivities can be found to be effective in reducing immunother-
protected by immunotherapy with yellow jacket apy reactions. Large local reactions occur in
venom alone.10 25% of children and 50% of adults, usually at
Venom immunotherapy is well tolerated. Most higher doses. Although troublesome, they do
patients receive their injections in an allergist’s of- not predict an increased risk of future systemic
fice until the maintenance dose is reached. Pa- reactions to treatment.
tients should remain for 30 minutes after each No long-term side effects have been associated
injection in a setting equipped to handle a sys- with venom immunotherapy thus far. It is safe
Allergy&Asthma
4. 30 Allergy to Insect Stings
Referral to an allergist is extremely important for leisure activities, medications, and coexistent dis-
eases should be considered); the conversion to a
diagnostic skin testing, patient education, and negative skin test is one criterion for stopping
venom immunotherapy. venom immunotherapy. For most patients, it is
time-based and discontinued after five years, after
which protection is long-lasting in most, even if
during pregnancy, with no increased risk of mis- the skin test remains positive. For those who had
carriage or congenital anomalies, and it does not a severe initial allergic reaction, a decision to con-
result in allergic sensitization in the child. tinue for longer or indefinitely may be made.
Recommendations regarding discontinuation
of venom immunotherapy include the following Conclusion
from the American Academy of Allergy Asthma Venom allergy is one of the most common causes
and Immunology: The decision to stop should be of anaphylaxis. All patients with a systemic aller-
made after thorough discussion by the physician gic reaction should be evaluated by an allergist for
and patient (patient variables such as vocation, consideration of immunotherapy.
References: study of the natural history of large local reactions after Hy-
1. Golden DB, Marsh DG, Kagey-Sobotka A, et al. Epidemiology of menoptera stings in children. J Pediatr 1984; 104:664–8.
Insect Allergy. JAMA 1989; 262: 240-4. 7. Light WC, Reisman RE, Shimizu M, et al. Unusual reactions fol-
2. Golden D, Marsh D, Freidhoff L, et al. Natural history of Hy- lowing insect stings: clinical features and immunologic analysis. J
menoptera venom sensitivity in adults. J Allergy Clin Immunol Allergy Clin Immunol 1977; 59:391–7.
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3. Deaths from each cause by 5-year age groups, race, and sex: test-negative patients. J Allergy Clin Immunol 1980; 67:400.
United States, 1980–1999. Hyattsville (MD): National Center 9. Hunt KJ, Valentine MD, Sobotka AK, et al. A controlled trial of
for Health Statistics. immunotherapy in insect hypersensitivity. N Engl J Med 1978;
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United States. J Allergy Clin Immunol 1973; 52:259–64. 10. Reisman RE, Livingston A. Venom immunotherapy: 10 years of
5. Birnbaum J,Vervloet D, Charpin D. Atopy and systemic reactions to experience with administration of single venoms and 50 micro-
hymenoptera stings. Allergy Proc 1994; 15(2):49-52. grams maintenance dose. J Allergy Clin Immunol 1992; 89:1189–
6. Graft DF, Schuberth KC, Kagey-Sobotka A, et al. A prospective 95.
Allergy&Asthma