Rocky Mountain Spotted Fever

Get CMERMSFTicks are disgusting (no offense ticks). They engorge themselves on our blood, becoming bloated sloth-like sacs of our serum. While that is certainly not appealing, what makes them most offensive is their tendency to transmit awful diseases to us.  These diseases (and unique conditions – Tick Paralysis) are numerous, but one of the most important to review (especially for those of us in North Carolina, USA) is Rocky Mountain Spotted Fever.


Rocky Mountain Spotted Fever (RMSF)

  • The Spotted Fever Group (SFG) of illnesses are caused by several Rickettsia species: [Biggs, 2016]
    • R. rickettsii
      • In the Eastern US, transmitted by Dermacentor variabilis (Dog Tick)
      • In the Western US, transmitted by Dermacentor andersoni (Rocky Mountain Wood Tick)
    • R. pakeri
      • Typically a more mild version of RMSF
      • Presents with inoculation eschar
      • Transmitted by Amblyomma maculatum (Gulf Coast tick)
    • Rickettsia species 364D
  • RMSF has the highest rates of severe and fatal outcomes of all of the rickettsiosis (in the USA). [Biggs, 2016]
    • Highest case-fatality rate is in children <10 years of age.
    • RMSF can occur in all ages and highest incidence is actually in the elderly.
  • Incidence of RMSF varies by geographic regions, with 63% of cases originating in 5 states: [Biggs, 2016]
    • Arkansas
    • Missouri
    • North Carolina
    • Oklahoma
    • Tennessee
    • So… not necessarily “Rocky Mountain!” 
    • Has also emerged recently in Arizona with high case-fatality rates in children.
  • RMSF is seasonal: 90% of cases occur between April and September.


RMSF Presentation

  • Initial symptoms are typically not specific (and, thus, requires our vigilance).
    • Symptoms appear 3-12 days after bite
    • For patients who end up with severe disease, incubation is shorter (< 5 days).
  • Initial symptoms include sudden onset of: [Biggs, 2016]
    • Fever, chills
    • Headache
    • Malaise, myalgia, anorexia
    • Nausea, vomiting, and abdominal pain
    • Photophobia
  • Rash? [Biggs, 2016]
    • Begins as small, blanching pink macule on ankles, wrists/forearms.
      • Then rash spreads to palms, soles, and up extremities.
      • Spares the face.
    • As illness progresses, the rash can develop associated petechiae (days 5-6).
    • Triad of Fever, Rash, and Tick Exposure is not commonly seen initially.
      • < 50% have a rash present within first 3 days of illness.
      • Rash typically appears 2-4 days after onset of fever, so patients may seek care before rash develops.
      • Some children will never develop a rash.
    • Eschar or ulcerative lesion may be present when associated with other SFG illness (ex, R. parkeri).


RMSF Late-stage Findings

  • RMSF leads to a systemic vasculitis, so multiple organs can be involved.
    • Meningoencephalitis
    • Acute Renal Failure
    • ARDS
    • Shock
    • Arrhythmia
    • Cutaneous necrosis
  • May become look similar to other conditions like Kawasaki or thrombocytopenic purpura.[Biggs, 2016]


RMSF Lab Findings

  • Common lab abnormalities include:
    • Thrombocytopenia (consumptive)
    • Hyponatremia (due to secretion of ADH and hypovolemia)
    • Increased (slightly) LFTs
    • Increased immature neutrophils
  • Lab findings are often normal early on in illness (so won’t help make the diagnosis early, when it needs to be treated).
  • Diagnostic tests for RMSF is not helpful during early stages of illness.


RMSF Treatment

  • Let’s make this simple… treatment is Doxycycline.
    • For kids <45 kg; dose = 2.2mg/kg Twice a Day
    • For patients >45 kg; dose = 100 mg Twice a Day
    • Treat for at least 3 days AFTER resolution of fever
  • Without appropriate therapy, RMSF progresses rapidly.
    • Early, empiric therapy is the best way to prevent RMSF progression. [Biggs, 2016]
    • Delays in diagnosis associated with:
      • Early presentation
      • Late-onset (or absence) of rash
      • Absence of headache (accentuation of GI symptoms)
  • Unfortunately, many providers often think Doxycycline cannot be given to children <8 years of age. [Zientek, 2014; O’Reilly, 2002]
    • Concerns for dental staining or enamel hypoplasia are often cited as reason to not use Doxycycline.
    • Doses appropriate for RMSF treatment have proven to be safe in children. [Todd, 2015].


Moral of the Morsel

  • RMSF is deadly, but initially presents with non-specific symptoms, making it challenging to detect.
  • Classic triad of fever, rash, and tick exposure should not be relied upon.
  • Relying on history of tick exposure (often not known) can obscure diagnosis.
  • Doxycycline is safe and effective in children! Don’t worry about the teeth!
  • Treat RMSF empirically!
  • Be vigilant during peak seasons: Summer-time “Headache and Fever” needs to have RMSF on the top of the DDx.



Biggs HM1, Behravesh CB, Bradley KK, Dahlgren FS, Drexler NA, Dumler JS, Folk SM, Kato CY, Lash RR, Levin ML, Massung RF, Nadelman RB, Nicholson WL, Paddock CD, Pritt BS, Traeger MS. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis – United States. MMWR Recomm Rep. 2016 May 13;65(2):1-44. PMID: 27172113. [PubMed] [Read by QxMD]

Alvarez-Hernandez G1, Murillo-Benitez C, Candia-Plata Mdel C, Moro M. Clinical profile and predictors of fatal Rocky Mountain spotted fever in children from Sonora, Mexico. Pediatr Infect Dis J. 2015 Feb;34(2):125-30. PMID: 25126856. [PubMed] [Read by QxMD]

Todd SR1, Dahlgren FS1, Traeger MS2, Beltrán-Aguilar ED3, Marianos DW1, Hamilton C4, McQuiston JH5, Regan JJ1. No visible dental staining in children treated with doxycycline for suspected Rocky Mountain Spotted Fever. J Pediatr. 2015 May;166(5):1246-51. PMID: 25794784. [PubMed] [Read by QxMD]

Zientek J1, Dahlgren FS2, McQuiston JH2, Regan J3. Self-reported treatment practices by healthcare providers could lead to death from Rocky Mountain spotted fever. J Pediatr. 2014 Feb;164(2):416-8. PMID: 24252781. [PubMed] [Read by QxMD]

Graham J1, Stockley K, Goldman RD. Tick-borne illnesses: a CME update. Pediatr Emerg Care. 2011 Feb;27(2):141-7; quiz 148-50. PMID: 21293226. [PubMed] [Read by QxMD]

Cale DF1, McCarthy MW. Treatment of Rocky Mountain spotted fever in children. Ann Pharmacother. 1997 Apr;31(4):492-4. PMID: 9101014. [PubMed] [Read by QxMD]


Sean M. Fox
Sean M. Fox
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