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Mosquito Bite: What Happens and Why It Itches?

Bite Mechanics

Female mosquito probes with fascicle (6 stylets: 2 maxillae, 2 mandibles, labrum, hypopharynx). Saliva injected via hypopharynx contains:

  • Anticoagulants: Apyrase (ADPase), anophelin — prevent platelet aggregation/clotting.
  • Vasodilators: Sialokinin, prostaglandins — increase blood flow.
  • Immunomodulators: D7 proteins, SG6 — suppress host hemostasis/inflammation.

Why It Itches

Salivary proteins are foreign antigens → IgE-mediated (immediate) and T-cell-mediated (delayed) hypersensitivity → mast cell degranulation → histamine, leukotrienes, cytokines → sensory nerve activation (itch) + vasodilation (wheal) + edema (flare).

Disease Transmission

Pathogens ingested in blood meal replicate in mosquito gut → migrate to salivary glands → injected in next bite.

  • Anopheles: Malaria (Plasmodium)
  • Aedes aegypti/albopictus: Dengue, Zika, chikungunya, yellow fever
  • Culex: West Nile, Japanese encephalitis

Symptom Relief

  • Wash with soap/water
  • Cold compress / ice pack
  • Topical: calamine, hydrocortisone 1%, pramoxine, menthol
  • Oral: cetirizine, loratadine, fexofenadine (2nd gen — less sedation)
  • Avoid scratching → prevents impetigo, scarring

Prevention

  • EPA-registered repellents: DEET 20–30%, Picaridin 20%, IR3535, Oil of Lemon Eucalyptus (PMD)
  • Permethrin-treated clothing
  • Eliminate standing water
  • Window screens, bed nets

When to Seek Care

Signs of infection (spreading redness, warmth, pus), systemic symptoms (fever, headache, myalgia, rash) after travel to endemic areas, anaphylaxis (rare).

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