What is Rocky Mountain spotted fever?

Rocky Mountain spotted fever, form of tick-borne typhus, caused by the bacterium Rickettsia rickettsii. Most of the reported cases have been in children.

Punam Jha
Other DiseasesWritten by: Punam JhaPublished at: Jul 20, 2013Updated at: Jul 20, 2013
What is Rocky Mountain spotted fever?

Rocky Mountain spotted fever (RMSF) is a tick-borne disease caused by a rickettsia (a microbe that differs somewhat from bacteria and virus).

A girl with Rocky Mountain Spotted feverRocky Mountain spotted fever, form of tick-borne typhus first described in the Rocky Mountain section of the United States, caused by a specific microorganism (Rickettsia rickettsii). Despite the name, the disease is not limited to the Rocky Mountains but rather occurs throughout most of the U.S. It is spread by the bite of an infected tick. It can also be transmitted by contamination of the skin with tick blood or feces.

The bacteria Rickettsia rickettsii that causes RMSF is transmitted by the dog tick (Dermacentor variabilis) in the eastern United States and by the wood tick (Dermacentor andersoni) in the Rocky Mountain States. On the West Coast, the lone star tick (Amblyomma americanum) also can transmit the bacteria.

Children aged 5 to 9 are more likely to be infected than any other age group.

How it affects the body parts

  • Once in the body, the bacteria attack and severely damage the linings of blood vessels. The injured vessels leak a watery fluid, which causes swelling.
  • The blood vessels also can lose blood, which causes potentially life-threatening hemorrhages (serious bleeding).
  • As damaged blood vessels continue to leak, blood pressure can decrease. If this happens, blood flow to the kidneys can decrease, causing kidney damage and, possibly, kidney failure.
  • Rocky Mountain spotted fever bacteria also may attack the brain directly, causing symptoms of encephalitis (brain infection) or meningoencephalitis (infection of the brain and its surrounding membranes).
  • Rocky Mountain spotted fever also can cause jaundice (yellowing of the skin and eyes) as a result of liver injury.
  • In the lungs, Rocky Mountain spotted fever can lead to an accumulation of fluid in the lungs (pulmonary edema) and severe breathing difficulties.

Possible Complications

  • Brain damage
  • Clotting problems
  • Heart failure
  • Kidney failure
  • Lung failure
  • Meningitis
  • Pneumonitis (lung inflammation)


Symptoms usually appear within two weeks of the bite of an infected tick. RMSF is characterized by a sudden onset of moderate to high fever (which can last for two or three weeks), severe headache, fatigue, deep muscle pain, chills and rash. The rash begins on the legs or arms, may include the soles of the feet or palms of the hands and may spread rapidly to the trunk or rest of the body.

It includes:

  • Chills
  • Confusion
  • Fever
  • Headache
  • Muscle pain
  • Rash -- usually starts a few days after the fever; first appears on wrists and ankles as spots

Other symptoms that may occur with this disease:

  • Diarrhea
  • Light sensitivity
  • Hallucinations
  • Loss of appetite
  • Nausea

When to Call a Doctor

Call the doctor immediately if you develop fever, headaches and nausea, with or without a rash, after you have been bitten by a tick or if you develop these symptoms and you have walked recently in tick-infested areas. The complications of untreated Rocky Mountain spotted fever are often life threatening.



Read more articles on Health A-Z.