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Key Features

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  • Allergic reactions to insects include

    • Symptoms of respiratory allergy as a result of inhalation of particulate matter of insect origin

    • Local cutaneous reactions to insect bites

    • Anaphylactic reactions to stings

  • Insect bites or stings

    • Can cause local or systemic reactions ranging from mild to fatal responses in susceptible persons

    • Frequency increases in the summer months and with outdoor exposure

  • Local cutaneous reactions include urticaria as well as papulovesicular eruptions and lesions that resemble delayed hypersensitivity reactions

  • Papular urticaria is almost always the result of insect bites, especially of mosquitoes, fleas, and bedbugs

  • Toxic systemic reactions consisting of gastrointestinal symptoms, headache, vertigo, syncope, convulsions, or fever can occur following multiple stings

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Clinical Findings

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  • Mild systemic reactions include

    • Itching

    • Flushing

    • Urticaria

  • Severe systemic reactions may include

    • Dyspnea, wheezing, chest tightness

    • Hoarseness, fullness in the throat

    • Hypotension

    • Loss of consciousness

    • Incontinence

    • Nausea, vomiting, and abdominal pain

  • Delayed systemic reactions occur from 2 hours to 3 weeks following the sting and include

    • Serum sickness

    • Peripheral neuritis

    • Allergic vasculitis

    • Coagulation defects

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Diagnosis

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  • Skin testing is indicated for children with systemic reactions to insect stings

  • Importantly, venom skin tests can be negative in patients with systemic allergic reactions, especially in the first few weeks after a sting, and the tests may need to be repeated

  • A positive skin test denotes prior sensitization but does not predict whether a reaction will occur with the patient's next sting nor does it differentiate between local and systemic reactions

  • Children who have had an allergic reaction commonly have positive skin tests for more than one venom

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Treatment

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  • For cutaneous reactions caused by biting insects

    • Cold compresses

    • Antipruritics (including antihistamines)

    • Potent topical corticosteroids (occasionally)

  • For stings

    • Carefully remove the stinger, if present, by flicking it away from the wound; avoid grasping in order to prevent further envenomation

    • Apply ice, elevate the affected extremity, and administer oral antihistamines, NSAIDs, and potent topical corticosteroids for local reactions

    • Topical application of monosodium glutamate, baking soda, or vinegar compresses is of questionable efficacy

  • For large local reactions, in which swelling extends beyond two joints or an extremity, a short course of oral corticosteroids may be required

  • Venom immunotherapy indicated for patients who experience severe systemic reactions and have a positive skin test

  • See also Anaphylaxis

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Outcomes

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Complications
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  • Secondary infection can complicate allergic reactions to insect bites or stings

  • Late sequelae to stinging insects

    • Serum sickness

    • Nephrotic syndrome

    • Vasculitis

    • Neuritis

    • Encephalopathy

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Prognosis
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  • Children generally have milder reactions than adults after insect stings, and fatal reactions are extremely rare

  • Patients aged 3–16 years with reactions limited to the skin, such as urticaria and angioedema, appear to be at low risk for more severe reactions with subsequent stings

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References

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Cox  L  et ...

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