Updated: 10/29/2017


Review Topic
  • A 9-year-old boy in Alabama presents with a pruritic red rash on his ankles and legs. He is currently on summer vacation and often rides his bike outdoors. He often plays in the fields and rarely applies anti-bug spray. He has had this rash for a few days now and reports that it is very itchy. Physical exam reveals multiple pink papulovesicles with surrounding erythema. Some lesions have overlying excoriations from scratching. He is given an oral antihistamine and told that this would resolve in time.
  • Clinical definition
    • pruritic skin reaction caused by 6-legged larvae of the trombiculid mite
  • Epidemiology
    • demographics
      • found in the southern United States
    • risk factors
      • exposure to grassy areas where mites are present
        • damp low-growing shrubs or tall grass or weeds
  • Etiology
    • infestation of the larval form of the mite Trombicula alfreddugesi
  • Pathogenesis
    • larvae can inject a proteolytic enzyme into the skin, which will cause a stylostome formation and itchiness
    • chiggers will remain attached to the stylostome for a few days
  • Associated conditions
    • scrub typhus if chiggers carry Rickettsia
      • more common in Asia
  • Prognosis
    • will self-resolve within 2 weeks
  • Symptoms
    • pruritus
  • Physical exam
    • bright red or pale rash with macules, papules, or papulovesicles
    • lesions typically occur ankles, back of the knees, or areas next to elastic bands of clothes (waistband or bra band)
      • if it occurs on the penis, the patient may have summer penile syndrome, where male children present with seasonal penile swelling and itching from chigger bites
  • Making the diagnosis
    • most cases are clinically diagnosed
  • Other bug bites (such as mosquito)
  • Contact dermatitis
  • Conservative
    • supportive care
      • indication
        • for all patients
      • modalities
        • ice or cold compress
        • topical antipruritics such as menthol or camphor
  • Medical
    • oral antihistamines
      • indication
        • if pruritus is not managed with a conservative approach
  • Secondary bacterial infection from scratching

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