Insect bites and stings

Definition

Insect bites and stings are injuries caused by the penetration of the skin by an insect's mouthparts or stinger, often accompanied by the injection of saliva, venom, or other substances. These reactions can range from mild local irritation to severe systemic allergic responses.

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Common Causative Insects

• Biting insects: Mosquitoes, fleas, lice, bedbugs, horseflies, blackflies

• Stinging insects: Bees, wasps, hornets, yellow jackets, ants

• Other arthropods: Mites, ticks, certain spiders and scorpions (though these are arachnids, not insects)

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Pathophysiology

Bites: Insects pierce the skin to obtain blood or feed on skin debris. Saliva contains anticoagulants, vasodilators, and enzymes that trigger local inflammatory responses.

Stings: Stingers inject venom, which may contain toxins, enzymes, and other proteins that cause local pain, swelling, and, in allergic individuals, systemic hypersensitivity reactions.

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Clinical Features

Local Reaction

• Redness, swelling, warmth, and pain or itching at the site

• Papules or urticaria (hives)

• Possible blistering or small necrotic areas in severe cases

Large Local Reaction

• Swelling extending beyond the sting site, sometimes involving an entire limb

• Usually peaks at 24–48 hours and resolves over 5–10 days

Systemic Allergic Reaction (Anaphylaxis)

• Generalized urticaria

• Angioedema

• Respiratory compromise (wheezing, throat tightness, laryngeal edema)

• Hypotension, dizziness, syncope

• Requires emergency management

Toxic Reactions

• Occur after multiple stings (e.g., bee swarm)

• Manifest as nausea, vomiting, diarrhea, headache, confusion, seizures, or organ failure due to systemic venom load

Infective Complications

• Secondary bacterial infection (e.g., cellulitis, impetigo) due to scratching or poor wound care

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Diagnosis

Diagnosis is clinical, based on:

• History of exposure

• Visible insect or stinger

• Characteristic skin lesions

• Timing of symptom onset

Investigations are generally unnecessary unless systemic symptoms suggest anaphylaxis or another medical emergency.

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Management

General First Aid

1. Remove the insect or stinger promptly (for bees, scrape rather than squeeze to avoid injecting more venom).

2. Clean the area with soap and water.

3. Apply a cold compress to reduce swelling and pain (10–15 minutes at a time).

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Local Reactions

Topical Treatments

• Hydrocortisone 1% cream: Apply thinly to affected area 2–3 times daily for up to 7 days.

• Calamine lotion or pramoxine-containing preparations: For itch relief.

• Topical antihistamines (e.g., diphenhydramine cream) can be used short-term, though risk of sensitization exists.

Oral Antihistamines

• Cetirizine 10 mg orally once daily

• Loratadine 10 mg orally once daily

• Chlorphenamine 4 mg orally every 4–6 hours (sedating; adjust in elderly)

Analgesics

• Paracetamol 500–1000 mg orally every 4–6 hours (max 4 g/day)

• Ibuprofen 200–400 mg orally every 6–8 hours (max 1200 mg/day OTC; higher under supervision)

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Large Local Reactions

• Oral corticosteroids may be considered if swelling is severe and functionally limiting:

  • Prednisolone 20–40 mg orally once daily for 3–5 days, then discontinue

• Continue antihistamines and analgesia as above

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Systemic Allergic Reactions (Anaphylaxis) – Medical Emergency

Immediate actions:

• Call emergency services

• Administer adrenaline (epinephrine) intramuscularly into the anterolateral thigh:

  • Adults: 0.3–0.5 mg (0.3–0.5 mL of 1:1000 solution)

  • Children: 0.01 mg/kg (max 0.3 mg per dose)

  • Repeat every 5–15 minutes as needed

• Position patient supine with legs elevated unless breathing is difficult

• Administer high-flow oxygen

• Establish IV access for fluids if hypotensive

Adjunctive treatments (do not delay adrenaline):

• Antihistamines (e.g., chlorphenamine 10 mg IV/IM in adults)

• Corticosteroids (e.g., hydrocortisone 200 mg IV in adults) to reduce biphasic reactions

• Bronchodilators (e.g., salbutamol nebulizer) for persistent bronchospasm

Patients with anaphylaxis should be monitored for at least 4–6 hours after symptom resolution, longer if risk factors for recurrence exist.

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Secondary Infection

If cellulitis develops:

• Flucloxacillin 500 mg orally every 6 hours for 5–7 days (first-line for skin infection in non-penicillin-allergic patients)

• Alternatives for penicillin allergy: Clarithromycin 500 mg orally twice daily for 5–7 days or Doxycycline 100 mg orally twice daily for 5–7 days (if appropriate for age and pregnancy status)

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Prevention

• Wear protective clothing in insect-prone areas

• Use insect repellents containing DEET, picaridin, or oil of lemon eucalyptus

• Avoid scented cosmetics or perfumes outdoors in high-risk environments

• Keep food and drinks covered outdoors

• Remove nests or hives from residential areas using professional pest control

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Special Considerations

• Individuals with a history of systemic allergic reactions to stings should be referred for allergy assessment and may require venom immunotherapy.

• Patients at risk of anaphylaxis should carry an adrenaline auto-injector (e.g., EpiPen 0.3 mg for adults, 0.15 mg for children) and receive training in its use.

• Children often have less severe reactions to stings compared to adults, but management principles remain similar.