Rocky Mountain Spotted Fever


Rocky Mountain spotted fever (RMSF) is the most common spotted fever rickettsiosis (SFR) in North America. It is associated with the highest rates of severe and fatal outcomes of all reportable rickettsial diseases in the United States (1)[A],(2)[C].


  • RMSF is a tick-borne systemic small and medium vessel vasculitis caused by the bacterium Rickettsia rickettsii (2)[C].
  • Symptoms include fever, headache, and myalgia followed by a macular rash; begins at wrists and ankles, spreading toward palms, soles, and the trunk
  • System(s) affected: cardiovascular, musculoskeletal, skin, central nervous system (CNS), renal, hepatic, and pulmonary


In the United States, ticks are both vectors and main reservoirs. Important species in the United States include the American dog tick, Dermacentor variabilis, in the eastern two-thirds of the United States; the Rocky Mountain wood tick, Dermacentor andersoni, in the western United States; and the brown dog tick, Rhipicephalus sanguineus, distributed throughout all states (1)[A],(3)[C].


  • In the United States, the annual incidence of SFR increased from 1.7 cases per million persons in 2000 to 13.2 in 2016. Cases have been reported in all states except Hawaii and Alaska. RMSF also seen in Canada, Mexico, and throughout Central and South America (4)[B].
  • Arkansas, Missouri, North Carolina, Tennessee, and Virginia account for over 50% of SFR cases. Cases have also been identified in Arizona where they had not previously (5).
  • Cases occur year round. Most cases are reported from May through August during the peak of outdoor activity (5).
  • Highest incidence occurs in age 60 to 64 years. Highest number of reported deaths is in children <10 years (5).

In the United States, 4,470 cases were reported in 2012. <0.1% of ticks carry virulent rickettsial species.

Etiology and Pathophysiology

  • An adult tick releases R. rickettsii, from its salivary glands after 6 to 10 hours of feeding.
  • Pathogens infect vascular endothelial cells, causing small and medium vessel injury throughout the body leading to disseminated inflammation. Subsequent vascular permeability can cause pulmonary and cerebral edema. Local consumption of platelets results in characteristic petechial rash.
  • Subsequent end-organ injury may also result in meningoencephalitis, ARF, acute respiratory distress syndrome, shock, arrhythmia, and seizure (1).
  • Symptoms appear 3 to 12 days after bite or between 4 and 8 days after discovery of an attached tick.
  • It is unknown whether R. rickettsii crosses the placenta and causes in utero infection.
  • RMSF can rarely be caused by direct inoculation of tick blood into open wounds or conjunctivae.

Risk Factors

  • Known tick bite, engorged tick, or presence of tick for >20 hours
  • Tick crushed during removal
  • Accumulated outdoor exposure or residence in wooded areas; contact with outdoor pets or wild animals

General Prevention

  • Limit tick exposure; highest tick exposure is in tall grasses, open areas of low bushy vegetation or wooded areas.
  • Wear light-colored clothing, long sleeves, pants, socks, and closed-toe shoes. Use DEET-containing insect repellents.
  • Permethrin spray on clothing
  • Regular tick checks, prompt and proper tick removal; do not use bare hands to remove ticks.
  • Wash hands and site of bite with soap and water after tick removal to avoid potential mucosal inoculation.
  • Protect pets through ectoparasite control (1)[A].

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