Updated: 5/24/2020

Rickettsial Diseases

Review Topic
  • A 30-year-old woman presents to the emergency room for a rash. She had been traveling and hiking in southern Europe. She does not recall having any tick bites but admits that it may be possible as she had many bug bites on her legs, though she attributed these to mosquitoes. She started having fevers 2 days ago along with a severe headache and developed a rash today. On physical exam, she has a maculopapular rash on her trunk as well as multiple eschars surrounding a bug bite on her left calf. She is started on doxycycline. (Mediterranean 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 the 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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