Rocky mountain spotted fever

Background

  • Most frequent rickettsial disease reported in the US.
  • Caused by Rickettsia rickettsii
    • Obligate intracellular, gram negative bacteria
    • Predilection for vascular endothelial cells
  • Spread by ticks
    • American Dog Tick (Dermacentor variabilis) Most common vector
    • Rocky Mountain Wood Tick (Dermacentor andersoni)
    • Brown Dog Tick (Rhipicephalus sanquineus)
    • Cayenne Tick (Amblyomma cajennense)
  • Seasonal distribution with most infections occurring in the summer months
  • Widely distributed in the US
    • States with the highest incidence are Oklahoma, Nebraska, Arkansas, Tennessee and North Carolina
  • Overall incidence is increasing while mortality is falling

Clinical Features

  • Symptoms generally begin 2-14 days after inoculation from an infected tick

Early symptoms

  • Non specific and highly variable
  • Fever
  • Nausea/Vomiting
  • Abdominal pain
  • Myalgias
  • Headache
  • Fatigue
  • Conjunctivitis

Late symptoms

  • Arthralgias
  • Rash
    • Begins as a blanching maculopapular rash that evolves to become a petechial rash
    • Usually 2-5 days after fever subsides
    • Starts on extremities and spreads inward
    • Can involve palms and soles

Complications

  • Secondary to host response against infected endothelial cells
    • Vasculitis
    • Myocarditis
    • Interstitial pneumonitis
    • Encephalitis

Diagnosis

  • Immunofluorescence
  • PCR
  • Titers

Work-Up

  • EKG (Myocarditis)
  • Chem 7 (Hyponatremia)
  • CBC (Thrombocytopenia)

Differential Diagnosis

Lower Respiratory Zoonotic Infections

Treatment

  • Doxycycline 100mg BID for 5-7 days
    • Children - 2.2mg/kg BID
  • Chloramphenicol 50-100 mg/kg/day div Q6hr (Max dose = 4g/day)

See Also

Source

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