Mosquito Bite Reaction

Mosquito bite reactions are hypersensitivity responses to salivary proteins injected during feeding, ranging from small wheals to large local swelling (Skeeter syndrome). Two reaction patterns occur: an immediate wheal within minutes and a delayed papule at 12 to 24 hours.

• Largest reactions occur in young children, immunocompromised people, those newly exposed to local species and rarely in EBV associated hypersensitivity.
• Mosquitoes transmit malaria, dengue, chikungunya, yellow fever, Rift Valley fever, filariasis, West Nile virus and others, so fever after bites needs assessment.

Itchy red wheal with central punctum at exposed skin, resolving in hours, or an indurated papule lasting several days.

• Skeeter syndrome: large (over 5 cm) swelling, warmth, blistering, mimicking cellulitis, with low grade fever, hours after bites.
• Differential diagnosis: cellulitis, flea or bedbug bites, other insect bites, papular urticaria, contact dermatitis, angioedema, scabies, urticaria.
• Complications: secondary bacterial infection (impetigo, cellulitis), ulceration, post inflammatory pigmentation, sleep disruption, anaphylaxis (rare), and mosquito borne infection.

Clinical.

• Malaria rapid diagnostic test or smear for any fever after exposure in an endemic area; consider dengue, chikungunya and Rift Valley fever by PCR or serology based on epidemiology.
• Swab if infected; C reactive protein and full blood count to differentiate cellulitis from Skeeter syndrome.

Symptomatic relief, infection control and prevention.

• Supportive: cold compress for 10 minutes, avoid scratching, keep nails short, elevate swollen limb, reassure.
• Pharmacological: hydrocortisone 1 percent or mometasone 0.1 percent cream once or twice daily for 5 to 7 days; oral cetirizine 10 mg daily (children 2 to 5 years 2.5 mg twice daily, 6 to 11 years 5 mg daily); for Skeeter syndrome prednisolone 0.5 to 1 mg/kg daily for 3 days and cetirizine; flucloxacillin 500 mg four times daily for 7 days only for confirmed secondary infection. Anaphylaxis: adrenaline 0.5 mg IM (adults), 0.01 mg/kg (children).
• Procedures: none.
• Special groups: pregnancy, repellents with DEET 20 to 30 percent and picaridin are acceptable, cetirizine acceptable; infants under 2 months, no DEET, use nets and clothing; immunocompromised, early review.
• Red flags: fever, headache, joint pain, bleeding, jaundice, altered consciousness, rapidly spreading redness, airway swelling.
• Follow-up: review in 1 week for large reactions. Prevention: insecticide treated nets, long clothing, screens, repellents (DEET 20 to 50 percent, picaridin 20 percent) and removal of standing water.