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  • Arthropods are defined by an exoskeleton, segmented body, and jointed appendages. Arthropods causing local and systemic reactions associated with their bites: Arachnida, Chilopoda, Diplopoda, and Insecta.

  • Cutaneous reactions to arthropod bites are inflammatory and/or allergic reactions.

  • Characterized by an intensely pruritic eruption at the bite sites, whether immediately or minutes to hours to days after the bite, persisting for days to weeks, manifested by solitary or grouped: Urticarial papules; papulovesicles; bullae. Persons are often unaware of having been bitten.

  • Systemic symptoms may occur, ranging from mild to severe, with death occurring from anaphylactic shock.

  • Arthropods are vectors of many systemic infections.


Four of nine classes of arthropods cause local or systemic reactions.

  1. Arachnida (four pairs of legs): Mites, ticks, spiders, and scorpions.

    1. Acarina. (mites and ticks) Sarcoptes scabiei (scabies). Demodex folliculorum and D. brevis (demodicidosis). Environmental mites. Ticks (Fig. 28-1) that feed on humans and are vectors for disease include blacklegged or Ixodes tick, Amblyomma americanum (lone star) tick, and Dermacentor (American dog or Wood) tick.

    2. Araneae. (spiders) Loxosceles reclusa or brown recluse spider. Latrodectus or black widow spiders. Tegenaria or hobo spiders cause necrotic arachnidism in the Pacific Northwest of United States. Tarantula: Mild inflammatory response to bite and to shed hairs.

    3. Scorpionida. Venom contains a neurotoxin that can cause severe local and systemic reactions.

  2. Chilopoda or centipedes.

  3. Diplopoda or millipedes.

  4. Insecta (three pairs of legs).

    1. Anoplura. Phthirius pubis or crab lice. Pediculus capitis or head lice. Pediculus corporis or body lice.

    2. Coleoptera. Beetles. Blister beetles contain the chemical cantharidin, which produces a blister when the beetle is crushed on the skin.

    3. Diptera. Mosquitoes, black flies (bites produce local reactions as well as black fly fever with fever, headache, nausea, generalized lymphadenitis), midges (punkies, no-see-ums, sand flies), Tabanidae (horseflies, deerflies, clegs, breeze flies, greenheads, mango flies); botflies, Callitroga americana, Dermatobia hominis, Phlebotomid sand flies, and tsetse flies.

    4. Hemiptera. Bedbugs and kissing bugs.

    5. Hymenoptera. Ants, bees, wasps, and hornets.

    6. Lepidoptera. Caterpillars, butterflies, and moths.

    7. Siphonaptera. Fleas, chigoe, or sand flea.

Figure 28-1

Comparison of blacklegged, lone star, and dog ticks Blacklegged or Ixodes nymphal ticks transmit Borrelia burgdorferi (Lyme disease) and other infections. Lone star ticks or Amblyomma americanum is the vector for anaplasmosis, tularemia, and Southern tick-associated rash illness. Dog or wood ticks, Dermacentor variabilis, transmit Rocky Mountain spotted fever and tularemia.


  • Lyme borreliosis, tularemia, and bubonic plague.

  • Scrub typhus, endemic (murine) typhus, spotted fever groups, and Q fever.

  • Human granulocytic anaplasmosis.

  • Tick-borne meningoencephalitis.

  • Leishmaniasis and trypanosomiasis (sleeping sickness or Chagas disease).

  • Malaria and babesiosis.

  • Filariasis, onchocerciasis (river blindness), and loiasis.


ERYTHEMATOUS MACULES Occur at bite sites and are usually ...

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