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Rocky Mountain Spotted Fever
by Michelle Badash, MS
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 TOP
Factors that increase your chance of RMSF include:
The first symptoms of RMSF often occur within 2-14 days after a tick bite and may include:
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.
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.
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. EBSCO DynaMed Plus website. Available at: http://www.dynamed.... Updated June 4, 2015. Accessed February 15, 2018.
Rocky Mountain spotted fever (RMSF). Centers for Disease Control and Prevention website. Available at:
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Updated December 9, 2016. Accessed February 15, 2018.
Last reviewed February 2018 by EBSCO Medical Review Board David L. Horn, MD, FACP
Last Updated: 1/13/2014
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