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  • A 24-year-old man presents to his primary care physician for a rash. He had been hiking in Tennessee during a retreat at his new job last week. He reports that he pulled a tick off of himself, though he did not think much of it at the time. Since then, he has had fevers and headaches daily. A few days after the onset of fever, he developed a rash that started on his wrists and ankles and now has spread to his chest. On physical exam, there are small blanching erythematous macules on his chest and petechiae on his extremities. His palms and soles are spared. He is started on empiric antibiotics. (Rocky Mountain spotted fever)
  • Classification
    • Rickettsia
      • spotted fever group (tick-borne)
        • Rickettsia rickettsii (Rocky Mountain spotted fever)
          • most common
        • Rickettsia conorii (Mediterranean spotted fever)
        • Rickettsia akari (Rickettsialpox)
        • Rickettsia africae (African tick bite fever)
      • typhus group
        • Rickettsia prowazekii (louse-borne epidemic typhus)
        • Rickettsia typhi (flea-borne murine typhus)
    • Orientia
      • scrub typhus group
        • Orientia tsutsugumushi (mite-borne)
          • formerly Rickettsia tsutsugamushi
    • obligate intracellular gram-negative bacteria
    • transmission via blood-feeding arthropod vectors
      • ticks, lice, and flea
  • Epidemiology
    • incidence depends on geographic distribution of the vector
    • North America (R. rickettsii and R. akari)
    • Europe (R. conorii)
    • Asia (R. conorii and O. tsutsugamushi)
    • Africa (R. africae and R. conorii)
    • South America (R. prowazekii)
    • worldwide (R. typhi)
  • Pathogenesis
    • the bacteria is transmitted into the human body via arthropod saliva when bitten
    • vascular endothelial cells are targeted by the bacteria
    • replication can cause local hemorrhage
  • Prognosis
    • most resolve with treatment
    • epidemic typhus (R. prowazekii) may recur (Brill-Zinsser disease)
    • Rocky Mountain spotted fever (R. rickettsii) has highest mortality
  • Symptoms
    • fever
    • rash
    • headache
  • Physical exam
Rickettsial Diseases
Clinical Manifestations of Rickettsial Diseases
Disease Vector Rash Eschar Regional Lymphadenopathy
Rocky Mountain spotted fever (R. rickettsii)
  • Tick
  • Macular
  • Petechial
  • Purpuric
  • Spreads centripetally (extremities to trunk)
  • No
  • No
Mediterranean spotted fever (R. conorii)
  • Tick
  • Macular
  • Papular
  • Purpuric
  • Yes
  •  No
Rickettsialpox (R. akari)
  •  Mite
  • Vascular
  • Papular
  • On trunk and extremities
  • Yes
  •  Yes
African tick bite fever (R. africae)
  •  Tick
  • Vesicular
  • Maculopapular
  • Yes, multiple
  •  Yes
Epidemic tyhpus (R. prowazekii)
  •  Louse
  • Macular
  • Papular
  • Petechial
  • Spreads centrifugally (trunk to extremities)
  • No
  • No
Murine typhus (R. typhi)
  •  Flea
  • Macular
  • Papular
  • Petechial
  • Spreads centrifugally
  • No
  •  No
Scrub typhus (O. tsutsugamushi)
  •  Mite
  • Macular
  • Pale
  •  Yes
  • Yes
  • Labs
    • detection of immunoglobulin G (IgG) is confirmatory
    • Weil-Felix test
      • serum cross-reacts with proteus antigens
    • may have thrombocytopenia and elevated liver function tests
  • Skin biopsy
    • visualization of infecting organism on tissue
  • Making the diagnosis
    • most cases are clinically diagnosed and confirmed with laboratory evaluation
  • Q fever
    • distinguishing factors
      • also an intracellular gram-negative bacteria
      • manifests as fever and pneumonia or endocarditis
      • does not manifest with rash
  • Management approach
    • empiric treatment is started as soon as possible
  • Medical
    • doxycycline
      • indication
        • first-line therapy
    • chloramphenicol
      • indication
        • contraindications to doxycycline
  • Neurologic sequelae
  • Peripheral gangrene
  • Reactive arthritis
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