USMLE

Rickettsia rickettsii

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Bacteria - Gram Negative
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Rickettsia rickettsii 

  • Characteristics
    • Gram negative
    • Obligate intracellular
  • Transmission
    • Vector is tick
      • Specifically by ticks of the Dermacentor family
      • Seen after exposure to infected dogs or outdoors settings
    • Occurs primarily in the South Atlantic states, especially North Carolina
      • Cases occur in western US, but is rarer
      • Contrast w/ Lyme disease caused by Borelia burgdorferi, a tick-mediated disease which occurs in Northeastern US
  • Presentation: Rocky Mountain spotted fever
    • Classic triad of headache, fever, rash
    • Rash spreads inwards (centripetally)
      • Starts at wrists and ankles (including palms and soles), moves to trunk
      • Palm + soles rash is also seen in secondary syphilis and Coxsackievirus A infection
      • Contrast w/ typhus (Rickettsia typhi + prowazekii), which present with rash that spares the palms and soles
  • Treatment
    • Doxycycline
      • Caution during pregnancy; alternative is chloramphenicol