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  • Arthropod bites and stings:
    • Cause a wide spectrum of reactions
    • Transmit local and systemic infections
  • Superficial infestations:
    • Epidermal: Pediculosis, scabies, tungiasis
    • Dermal: Larva migrans, myiasis

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  • Terrestrial arthropods that bite/sting humans: arachnids, centipedes, millipedes, insects.
  • Cutaneous reactions to arthropod bites (CRAB) are inflammatory and/or allergic reactions.
  • Characterized by an intensely pruritic eruption at the bite sites immediately to minutes to hours to days after the bite, persisting for days to weeks, manifested by solitary or grouped:
    • Urticarial papules
    • Papulovesicles
    • Bullae
  • Patients are often unaware of having been bitten.
  • In some cases, systemic symptoms may occur, ranging from mild to severe, with death occurring from anaphylactic shock.
  • Arthropods are vectors of many systemic infections.

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Epidemiology

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Season

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Summer in temperate climates.

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Etiology

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5 of 9 classes of arthropods cause local and systemic reactions associated with their bites: Arachnida, Chilopoda, Diplopoda, Crustacea, Insecta.

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Arthropods that Bite, Sting, or Infest

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  • Arachnida (four pairs of legs): mites, ticks, spiders, scorpions
    • Acarina
      • Mites: Sarcoptes scabiei causes scabies; Demodex folliculorum, human hair follicle mite; many others including food, fowl, grain, straw, harvest, animal, and house dust mites.
      • Ticks
    • Araneae: spiders
    • Scorpionida
  • Chilopoda and Diplopoda: centipedes, millipedes
  • Insecta (three pairs of legs)
    • Anoplura: lice (Phthirius and Pediculus)
    • Coleoptera: beetles
    • Diptera: mosquitoes, black flies, midges (punkies, no seeums, sand flies), Tabandae (horseflies, deerflies, clegs, breeze flies, greenheads, mango flies); botflies, Callitroga americana, Dermatobia hominis, phlebotomid sand flies, tsetse flies
    • Hemiptera: bedbugs, kissing bugs
    • Hymenoptera: ants, bees, wasps, hornets
    • Lepidoptera: caterpillars, butterflies, moths
    • Siphonaptera: fleas, chigoe or sand flea

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Arthropod-Borne Infections

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  • Lyme borreliosis, tularemia, bubonic plague.
  • Scrub typhus, endemic (murine) typhus, spotted fever groups, Q fever
  • Human granulocytic anaplasmosis,
  • Tick-borne meningoencephalitis
  • Leishmaniasis, trypanosomiasis (sleeping sickness, Chagas disease).
  • Malaria, babesiosis.
  • Filariasis, onchocerciasis (river blindness), loiasis

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Geographic Distribution

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Worldwide.

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Pathogenesis

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Mites

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  • Produce pruritus and/or allergic reactions through salivary proteins deposited during feeding.
  • Harvest mites (chiggers) may present as intense pruritus on the ankles, legs, belt line; mites usually fall off after feeding or may be scratched off.
  • In nonsensitized individuals, 1- to 2-mm pruritic papules are seen.
  • In sensitized individuals, CRAB may be papular urticaria, vesiculation, or granulomatous reaction with fever and lymphadenopathy.

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Ticks (Acarina)

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Reactions include foreign body reactions, reactions to salivary secretions, reactions to injected toxins, and hypersensitivity reactions. Tick paralysis is caused by a toxin secreted in the saliva of the tick.

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Spiders (Araneae)

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  • Loxosceles reclusa: Brown recluse spider bite causes reactions ranging from mild urticaria to full-thickness necrosis (loxoscelism).
  • Latrodectus: “Widow” spiders inject a venom that contains a neurotoxin (α-latrotoxin) producing reactions at the bite site ...

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