Insect Allergy

Key Features

• 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

Clinical Findings

• 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

Diagnosis

• 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

Treatment

• 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

Outcomes

Complications

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

• Late sequelae to stinging insects

  • Serum sickness

  • Nephrotic syndrome

  • Vasculitis

  • Neuritis

  • Encephalopathy

Prognosis

• 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

References