Rocky Mountain Spotted Fever



Rocky Mountain spotted fever (RMSF) is a severe rickettsial infectious disease that affects your blood vessels. It is potentially fatal.

Ticks in North, Central, and South America spread the disease.


RMSF is caused by specific rickettsial bacteria. The American dog tick and the Rocky Mountain wood tick carry these bacteria. It passes to humans when an infected tick bites the skin. The bacteria can then pass into the bloodstream.

The bacteria sit in the lining of small blood vessels and multiply. The growth of the bacteria causes irritation and swelling in the blood vessels. Blood and other fluids can then leak out of the blood vessels into the surrounding tissue.

Risk Factors

Factors that increase your chance of RMSF include:

  • Being outdoors in areas known to have RMSF especially from April to September
  • Exposure to tick-infested areas such as long grass, weeds, or low brush
  • Exposure to dogs
  • Not using preventive steps (listed below)



The first symptoms of RMSF often occur within 2-14 days after a tick bite and may include:

  • Fever
  • Headache
  • Rash
  • Nausea and vomiting
  • Abdominal pain
  • Muscle or joint pain
  • Lack of appetite
  • Red eyes
  • Light hurting the eyes
  • Fatigue
  • Altered mental status
  • Severe bleeding
  • Difficulty breathing

Most but not all people with RMSF develop a rash. The rash begins as small, flat pink spots but can later progress to red-purple spots. The rash most often starts on the wrists, forearms and ankles.

If left untreated, RMSF can cause severe problems to organs or skin near the leaky blood vessels. Symptoms will depend on which organs are involved.

Immune System Including Spleen and Lymph Nodes
Immune system
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You will be asked about your symptoms and medical history. A physical exam will be done. RMSF can be difficult to diagnose because the symptoms are similar to many other diseases and the rash may not be there at first. Many people do not realize they have been bitten by a tick, which can also make the diagnosis more difficult.

A blood test may be done to confirm the diagnosis if your doctor suspects RMSF. Other tests, like a complete blood count and electrolytes, may be done to evaluate the severity of the disease. A spinal tap may be done to look for infection in the spinal fluid.



Treatment may be started before a clear diagnosis is made based on your risk and fever.

RMSF is treated with antibiotics. It is important to start this treatment early. Make sure to take all of your medication as advised.


The best way to prevent RMSF is to limit your exposure to ticks. If you live in an area that is prone to ticks, take the following precautions:

  • Wear light-colored clothing. This makes ticks are more visible.
  • Tuck pant legs inside socks. This stops ticks from crawling up under your pants.
  • Apply insect repellents containing DEET (applied to exposed skin). Apply permethrin to clothing.
    • For young children, DEET should be avoided or used sparingly. Carefully follow the directions on the label.
  • Carefully check your entire body for ticks after returning from outdoor areas.
  • Check pets for ticks.

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Edits to original content made by Denver Health.

a (RMSF)


Centers for Disease Control and Prevention 

Family Doctor—American Academy of Family Physicians 


Public Health Agency of Canada 

The College of Family Physicians of Canada 


Rocky Mountain spotted fever. Centers for Disease Control and Prevention website. Available at: Updated November 4, 2010. Accessed January 15, 2015.

Rocky Mountain spotted fever. EBSCO DynaMed Plus website. Available at: . Updated June 4, 2015. Accessed September 13, 2016.