Skip to main content

Rocky Mountain Spotted Fever

American Dog Tick

What is Rocky Mountain spotted fever?

  • Rocky Mountain spotted fever (RMSF) is a bacterial disease caused by the bacterium, Rickettsia rickettsii.  
  • RMSF is one of the deadliest tickborne diseases in the U.S.
  • RMSF is transmitted by ticks, most commonly the American dog tick (Dermacentor variabilis).  
  • The American dog tick is the most common tick in Michigan, human cases of RMSF are rare but do occur.  
  • Rocky Mountain spotted fever can be fatal if treatment is not started within the first 5 days of illness.  
  • Physicians in Michigan who suspect RMSF should begin treatment with doxycycline immediately and not wait for results of laboratory testing.
  • Preventing tick bites is the best way to avoid getting RMSF.

    • Got A TICK? SUBMIT IT FOR ID, Information on identifying and testing ticks

      GOT A TICK? SUBMIT A PIC! Click here for more information on picture ID

      MiTracking, Michigan Environmental Public Health Tracking

      Emerging and Zoonotic Disease Surveillance Summary

      Link to 2021 Michigan Trends in Tickborne Disease Report


      • RMSF is the deadliest tick-borne disease in the U.S.
      • It is spread by several ticks in the U.S. including the American dog tick, Rocky Mountain wood tick, and the brown dog tick (parts of the SW U.S. and Mexico). 
      • Anyone living or recreating where these ticks are present may be at risk. 
      • Rocky Mountain spotted fever has been diagnosed throughout the U.S., however cases are most commonly reported from North Carolina, Tennessee, Missouri, Arkansas, and Oklahoma. 
      • Children under 10 years old, American Indians, people with a compromised immune system, and people with delayed treatment are at an increased risk of fatal outcome from RMSF. 
      • The majority of cases reported have an illness onset during the months of June and July.  However, the seasonality varies for different regions of the country.    


    • What are the signs and symptoms of RMSF?

      • Early symptoms can be non-specific, including fever and headache, but can rapidly progress and become life threatening.
      • See your healthcare provider if you become ill after a tick bite or having been in the brushy or woodsy areas where ticks commonly live.
      • The first symptoms of Rocky Mountain spotted fever (RMSF) typically begin 2-14 days after the bite of an infected tick. 
      • The disease is characterized by acute fever, headache, muscle pain, vomiting, and general discomfort. 
      • A rash may also develop 2-4 days after the fever begins and often spreads with time. 
      • Approximately 90% of infected individuals will develop some type of rash, however, the rash may not develop until later in the disease process. 
      • RMSF can be life-threatening, but early treatment with doxycycline can prevent disability and death.
      • Some patients who survive RMSF can be left with long term health effects including neurological deficits, damage to internal organs, and vascular damage requiring amputation of some extremities.



      How is RMSF diagnosed? 

      • Early symptoms of RMSF may resemble other diseases. 
      • Diagnostic tests, especially those based on the detection of antibodies, will often appear negative for the first 7-10 days of illness. 
      • The diagnosis of RMSF is based on clinical suspicion alone. 
      • Treatment is most effective at preventing death if started in the first five days of symptoms.
      • The diagnosis must be made and treatment initiated based on clinical signs and symptoms, and can later be confirmed using specialized confirmatory laboratory tests.
      • Rickettsial Disease Testing and Interpretation

      What should I do if I have a tick that I want to identify?

      • Knowing what kind of tick bit you may be important in knowing what your risk of disease is.  
      • The Michigan Department of Health and Human Services (MDHHS) provides tick identification at no charge to Michigan citizens.
      • There are two ways to have a tick identified, 1) By submitting a photo of your tick, or, 2) by sending the tick to the MDHHS for microscopic identification. 
      • If you want to submit a photo of your tick, the MDHHS will make all attempts to identify the tick based on the condition of the tick and the condition of the photos. 
      • Definitive tick identification may only be made by sending the tick for microscopic examination.  

      Click HERE for instructions on how to submit a photo of your tick for identification

      Click HERE for instructions on how to ship a tick to the MDHHS for microscopic identification

      RMSF information for clinicians

       CDC:  Tickborne Diseases of the United States

      The Michigan Department of Health and Human Services Bureau of Laboratories can assist Michigan healthcare providers with RMSF diagnostic testing:

      MDHHS BOL Mosquito-Borne and Tick-Borne Disease Testing



      What is the treatment for RMSF?

      Treatment should never be delayed pending the receipt of laboratory test results, or be withheld on the basis of an initial negative finding. 

      • The antibiotic doxycycline is the first line treatment for adults and children of all ages and should be initiated immediately whenever RMSF is suspected.
      • Treatment is most effective at preventing severe complications, including death, if started within the first 5 days of symptoms. 
      • Treatment should continue for at least 3 days after the fever subsides and there is evidence of improvement for a minimum of 5-7 days.


    • There is no vaccine to prevent RMSF.

      Prevent illness from RMSF by preventing:

      Tick Bites

      Ticks on your Pets

      Ticks in Your Yard:  The Tick Management Handbook- Connecticut Agricultural Experiment Station




    • Michigan Resources

      • Ticks and Your Health - Brochure describing Lyme disease and other tick-borne diseases in Michigan. Other topics covered include tick-bite prevention, preventing ticks on pets, and landscape techniques to minimize tick risk.
      • Michigan's Five Most Common Ticks
      • Michigan Tick ID Card - Pocket-sized card for identifying common ticks in Michigan. Information regarding tick removal and tick-bite prevention.

      Centers for Disease Control and Prevention Resources

      For the Public

      For Healthcare Providers