Rocky Mountain Spotted Fever


Tick-borne rickettsial diseases include spotted fever rickettsiosis (SFR), ehrlichiosis, and anaplasmosis. In the United States, Rocky Mountain spotted fever (RMSF) is the SFR associated with the most severe and fatal outcomes (1)[A].


  • RMSF is a tick-borne illness caused by the bacterium Rickettsia rickettsii (2)[C].
  • Symptoms include fever, headache, and a petechial or maculopapular rash that typically begins at wrists and ankles, spreading toward palms, soles, and the trunk.
  • System(s) affected: cardiovascular, musculoskeletal, skin, 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 (the most common vector) found in eastern, central, and pacific coastal areas; the Rocky Mountain wood tick, Dermacentor andersoni, found in the western United States; and the brown dog tick, Rhipicephalus sanguineus, distributed throughout all states. Although it can be seen throughout the United States, RMSF is the most common in the southeastern and south-central United States (1)[A].


  • 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 is also seen in Canada, Mexico, and throughout Central and South America (3)[B].
  • Arkansas, Missouri, North Carolina, Tennessee, and Virginia account for >50% of SFR cases. There has also been increasing prevalence in Arizona, likely due to the brown dog tick (1).
  • Cases occur year round. Most cases are reported from May through August during the peak of outdoor activity.
  • Highest incidence occurs in those aged >40 years. Highest number of reported deaths is in children aged <10 years.

In the United States, 5,207 cases were reported in 2019, although the highest peak was in 2017 with 5,248.

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 edema, cerebral edema, and hyponatremia. Local consumption of platelets and the small vessel injury results in the characteristic petechial rash.
  • Subsequent end-organ injury may also result in meningoencephalitis, acute renal failure, acute respiratory distress syndrome, shock, arrhythmia, and seizure (1).
  • 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 or fluid into open wounds or conjunctivae or through inhalation of contaminated aerosols.

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, particularly dogs, 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-toed shoes. Use 20–30% 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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