Rocky mountain spotted fever


American dog tick
  • Most frequent rickettsial disease reported in the US.[1]
  • 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[2]
    • Prior to the era of antibiotics, ~30% mortality
    • Currently mortality is 3-5%

Clinical Features

  • Symptoms generally begin 2-14 days after inoculation from an infected tick[3]

Early symptoms

Late symptoms

Rocky mountain spotted fever rash
  • 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 (centripetally)
    • Can involve palms and soles (50% of cases)
  • Arthralgias
  • Positive Rumpel-Leede test
    • Development of petechiae at the site of blood pressure cuff and distally after compression


Differential Diagnosis

Lower Respiratory Zoonotic Infections

Tick Borne Illnesses


  • PCR (initially)
  • Serial serologic examinations by indirect fluorescent antibody confirm the diagnosis
  • Titers



  • Doxycycline 100 mg BID for 5-7 days[4]
    • Indicated also in children at 2.2mg/kg BID
  • Chloramphenicol (CAM) 50-100 mg/kg/day div Q6hr (Max dose = 4g/day)
    • Preferred agent in pregnancy. May cause aplastic anemia and Grey baby syndrome, more common in near term or 3rd trimester[1]
    • Consideration should be made for doxycycline over CAM in the 3rd trimester


See Also


  1. 1.0 1.1
  2. Columbia University Irving Medical Center. Rocky Mountain Spotted Fever.
  4. Shandera WX, Roig IL: Viral & Rickettsial Infections, in Papadakis MA, McPhee SJ (eds): Current Medical Diagnosis and Treatment, ed 52. USA, McGraw-Hill, 2013, (Ch) 32: p 1412-1413.