ALLERGIC REACTIONS TO INSECT STINGS

ALLERGIC REACTIONS TO INSECT STINGS

  1. 1
    Current Diagnosis
    • Determine the insect involved by recording circumstances of sting event.
    • Determine the type of reaction: usual (expected), large local, or systemic (anaphylaxis).
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  2. 2
    Current Therapy
    • Treatment for usual reactions
      • H1-antihistamines, analgesics, cold compresses
      • Discussion of avoidance measures
    • Treatment of large local reactions
      • H1-antihistamines, analgesics, cold compresses
      • Discussion of avoidance measures and possible prescription of epinephrine autoinjectors (e.g., Auvi-Q, EpiPen)
    • Treatment of systemic reactions
      • Epinephrine
      • Supplemental therapy, including antihistamines, β-adrenergics, oxygen, intravenous fluids, and perhaps vasopressors
      • Patients on β-blockers may require glucagon (e.g., Glucagon Emergency Kit, GlucaGen HypoKit)
      • Discussion of avoidance measures, medical alert accessories, prescription for epinephrine autoinjectors
      • Referral to allergist-immunologist to evaluate for specific IgE and possible institution of immunotherapy

    Most stinging insects belong to the order Hymenoptera. They include species of bees (genus Apis, including honey bees and bumblebees), wasps (genus Polistes), yellow jackets (genus Vespula), hornets (genus Dolichovespula), and fire ants (genus Solenopsis).

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  3. 3
    Diagnosis

    There are two important historical points to ascertain when seeing a patient with an allergic reaction to a stinging insect. The first is the type of insect that caused the sting. The physician may not rely on the patient’s identification. Clues about the type of insect can be obtained from the circumstances of the sting.

    Bees are herbivores and not aggressive. Stings from these insects often occur in fields with flowering plants when a barefoot patient steps or accidently sits on them. Bees have a barbed stinger and attached venom sac, which may be left in place after a sting. These should be removed immediately with a scraping motion; any pinching of the sac may inject additional venom.

    Yellow jackets are aggressive scavengers and are found wherever food is left in the open. Stings from these insects usually occur in picnic areas or around open garbage containers. Like bees, yellow jackets occasionally leave a stinger in place, so this historical feature is not definitive. Wasps usually are not aggressive, except in defense of their nests. However, they tend to build these nests under the eaves and overhangs of our homes, and people stung by wasps are usually entering or exiting their homes.

    Hornets are not as aggressive, except in defense of their nest.

    Because the nests are built in trees, stings by these insects are rarer.

    Fire ants are very aggressive in defense of their nests, which are low mounds built above ground with extensive tunnels beneath the surface. In endemic areas (mostly the southeastern United States), they swarm and attack as a group when disturbed. Patients stung by fire ants are usually outdoors and accidently stand in a mound or disturb a mound while working or playing in their yard or garden.

    Fire ant workers do not fly. They bite only to get a grip and then sting from the abdomen and inject a toxic alkaloid venom. Because they attack as a group, they are usually seen and clearly identified by the patient. The size of the fire ants means their venom is injected less deeply than that of other hymenoptera, which leads to the usual development of a pseudopustule about 24 hours after a sting. These pseudopustules contain necrotic cellular material but are sterile because fire ant venom has antibiotic properties that can kill bacteria and fungi. The pseudopustules should be left alone; opening and draining them only increases the risk of secondary infection.

    The second historical point is the type of reaction by the patient to the sting. The active venom components produce immediate swelling, redness, and tenderness with fairly intense pain at the site of the sting that slowly resolves over several hours. Sometimes, the immediate reaction progresses, and swelling (>10 cm) continues for 1 to 2 days and extends across several contiguous joints away from the site of the sting. This large local reaction may take 5 to 10 days to fully resolve, and it may be difficult to differentiate this from a secondary infection. Large local reactions peak in 1 to 2 days and then slowly recede, whereas secondary infections continue to get worse. Large local reactions do not cause systemic fever or lymphangitis, which should be treated with antibiotics if they occur.

    The reaction of most concern is anaphylaxis. Unfortunately, many of the symptoms are similar to those of anxiety, which also may occur in a concerned patient: feelings of impending doom, a rapid heartbeat, shortness of breath, and nausea. Other symptoms that should not be seen in anxiety include a metallic taste, pruritus, and abdominal or uterine cramping. Signs of anaphylaxis include flushing, urticaria, angioedema, vomiting, diarrhea, bronchospasm, hypotension, and shock. Diagnosis of anaphylaxis requires involvement of 2 organ systems out of cutaneous, pulmonary, gastrointestinal or cardiovascular or a drop in blood pressure after a known allergen exposure. Involvement of the upper airway and cardiopulmonary systems is associated with death, and hymenoptera stings are the cause of about 40 deaths per year in the United States. Documentation of the type of reaction is essential for future risk assessment and determination of whether prophylactic therapy should be offered.

    The risk for a systemic reaction after hymenoptera sting in the general population is estimated to be 3% to 5%. In patients who have a documented large local reaction to an insect sting or a generalized cutaneous reaction (hives angioedema without other organ system involvement), the risk of systemic reactions increases slightly to about 10%. Patients suffering large local reactions or generalized cutaneous reactions, may be referred to a specialist for specific IgE testing. For patients who have suffered anaphylaxis, the risk of systemic reactions after a sting is 50% to 60%. If a patient has suffered an anaphylactic event after a hymenoptera sting and has specific IgE to that hymenoptera as determined by in vivo (skin testing) or in vitro methods and is then placed on immunotherapy for that insect, the risk of systemic reaction after another sting is only 2% to 3%.

    Immunotherapy entails the use of specific venom products for each species, with the exception of fire ants. Because of the difficulty in extracting venom from fire ants, the only commercially available product for fire ants is the whole-body extract. Although whole-body extract is not effective therapy for other hymenoptera, it has been shown to be effective for fire ants.

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  4. 4
    Treatment

    Immediate therapy for insect stings depends on the type of reaction. For the expected short-duration local reaction, treatment includes cold compresses; antihistamines, such as diphenhydramine (Benadryl 25– 50 mg for adults; 1 mg/kg [up to 50 mg] for children) or cetirizine (Zyrtec 10 mg for adults and children older than 6 years; 5 mg for children younger than 6 years); and analgesics, such as acetaminophen (Tylenol) or ibuprofen (Motrin). Avoidance of future stings may be discussed with the patient. Recommendations include the following:

    • Remove wasps’ nests from around the home, especially near doorways.
    • Avoid areas near open garbage.
    • Do not leave open food or drinks during outdoor eating.
    • Wear shoes, socks, and work gloves when working in the yard or garden.

    Large local reactions may be treated as described for short-duration local reactions, with the addition of a short course (5–7 days) of oral steroids (e.g., Medrol dose pack), especially if there is significant morbidity associated with the site of the reaction. For instance, if a hand or foot is involved, a patient may not be able to write, work, or walk for up to a week. Avoidance measures should be discussed.

    Epinephrine auto-injectors (e.g., EpiPen, EpiPen Jr, Adrenaclick, Auvi-Q) may be given, depending on the patient’s anxiety about future stings. Epinephrine auto-injectors are simple devices with instructions clearly printed on them, but mistakes in usage do occur. The most common include “bouncing” the injector off the leg, which ejects the epinephrine onto the leg instead of delivering it intramuscularly, and putting the thumb over the end of the injector, which if the injector is reversed leads to no delivery of epinephrine and thumb trauma. The auto-injector Auvi-Q provides audible instructions to the user. Demonstration pens and videos of proper technique may be obtained from the manufacturers (e.g., Amedra, Mylan, Sanofi).

    The primary treatment of anaphylaxis is epinephrine (1:1000 concentration), with 0.3 to 0.5 mL given intramuscularly in adults or 1.1  mL/kg in children (less than 30 kg) every 5 to 15 minutes as needed. The patient should be placed in a recumbent position with the feet elevated. Supplemental therapy includes antihistamines (i.e., H1- receptor antagonists); H2-blockers (e.g., ranitidine [Zantac1] 150 mg PO) for cutaneous signs and symptoms; β-adrenergics (e.g., albuterol [Proventil, AccuNeb]) administered by metered-dose inhaler or nebulizer for bronchoconstriction; oxygen for hypoxia; intravenous fluids and possibly vasopressors for hypotension; and intubation for compromise of the upper airway.

    In patients who have suffered prior anaphylaxis physicians must avoid the tendency to treat the initial cutaneous-only symptoms with antihistamines alone, because cutaneous signs and symptoms often develop rapidly into life-threatening events. When a patient has a prior history of anaphylaxis to insect stings, the appropriate therapy is epinephrine even if the initial presenting symptoms are cutaneous only. Most anaphylaxis responds quickly to a single dose of epinephrine, although up to 30% of anaphylaxis cases require two or more doses. Because anaphylaxis may be prolonged and last hours and epinephrine has a short duration of action (1 hour), patients should be observed for 4 to 6 hours after the last epinephrine dose.

    They should remain symptom free during that time before being released from the clinic or emergency department. In 3% to 20% of patients, a biphasic reaction occurs with recurrence of signs and symptoms 4–6 hours (range, 1–72 hours) after the initial reaction. For patients with prolonged or severe reactions, which are more often associated with a recurrence, overnight admission for observation should be considered.

    Oral (prednisone 1 mg/kg up to 50 mg daily) or intravenous (methylprednisolone [Solu-Medrol] 1–2 mg/kg every 6 hours) steroids are sometimes given to minimize recurrences. Many patients are on β- blocking agents, which may make patients suffering anaphylaxis refractory to treatment with epinephrine. In this case, glucagon (e.g., GlucaGen HypoKit, Glucagon Emergency Kit1) at a dose of 1 to 5 mg (20–30 µg/kg [maximum 1 mg] in children)3 may be tried intravenously over 5 minutes, followed by infusions (5–15 µg/min)3 titrated to clinical response. Patients who have suffered anaphylaxis must be given instructions on avoidance of future stings, epinephrine pen autoinjectors (EpiPen), and information on medical alert accessories (e.g., necklaces, bracelets). They should also be referred to an allergist-immunologist to evaluate them for the presence of specific IgE, counseling, and consideration of immunotherapy, which may significantly reduce their future risk.

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  5. 5
    References

    Freeman T.M. Hypersensitivity to hymenoptera stings. N Engl J Med. 2004;351:1978–1984.

    Freeman T.M., Hylander R.D., Ortiz A.A., Martin M.F. Imported fire ant immunotherapy: Effectiveness of whole body extracts. J Allergy Clin Immunol. 1992;90:210–215.

    Golden D.B.K., Demain J., Freeman T., et al. Stinging insect hypersensitivity: A practice parameter update 2016. Ann Allergy Asthma Immunol. 2017;118:28–54.

    Hunt K.J., Valentine M.D., Sobotka A.K., et al. A controlled trial of immunotherapy in insect hypersensitivity. N Engl J Med.

    1978;299:157–161.

    Sampson H.A., Munoz-Furlong A., Campbell R.L., et al. Second symposium on the definition and management of anaphylaxis: Summary report—Second National Institute of

    Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium. J Allergy Clin Immunol. 2006;117:391– 397.

    Schuberth K.C., Lichtenstein L.M., Kagey-Sobotka A., et al.

    Epidemiologic study of insect allergy in children. II. Effects of accidental stings in allergic children. J Pediatr. 1983;102:361– 365.

    1  Not FDA approved for this  indication.

    3  Exceeds dosage recommended by the  manufacturer.

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