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Rocky Mountain Spotted Fever

Medically reviewed by Last updated on Dec 29, 2021.

What is Rocky Mountain Spotted Fever?

Harvard Health Publishing

Rocky Mountain spotted fever is a severe illness caused by tiny bacteria called Rickettsia rickettsii, which are transmitted through the bite of an infected tick. In the eastern United States and in California, the infected tick is usually Dermacentor variabilis, the American dog tick. In most of the western United States, the tick is more likely to be Dermacentor andersoni, the Rocky Mountain wood tick. Humans typically become infected in the spring and early summer.  

Once someone is bitten by an infected tick, Rocky Mountain spotted fever bacteria can spread throughout the bloodstream and lymphatic system. The tick must remain attached and be actively feeding to transmit the bacteria. Not everybody who is bitten by an infected tick develops Rocky Mountain spotted fever. It is not clear why some people get the disease and others do not. 

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.  

The U.S. Centers for Disease Control and Prevention (CDC) up to 4000 cases of Rocky Mountain spotted fever or related infections in the United States each year. Children aged 5 to 9 are more likely to be infected than any other age group.  


Typically, symptoms begin 2 to 14 days after a tick bite, with an average of 1 week. During the first 3 days of symptoms, an infected person usually has a fever of more than 102 degrees Fahrenheit and a severe headache. Muscle aches, nausea and vomiting are common. Between the 3rd and 5th day of fever, most people develop a rash, which usually begins on the wrists and ankles, then spreads to the arms, legs and trunk. In about two-thirds of patients, the rash also involves the palms of the hands and the soles of the feet. On day 6 or later, the areas of rash may show tiny broken blood vessels and small hemorrhages under the skin.  

Other symptoms of Rocky Mountain spotted fever include:  

  • Lungs—Rapid breathing, severe shortness of breath, bluish tint to fingernails and lips  
  • Liver and gastrointestinal tract—Abdominal pain, nausea, vomiting, diarrhea and jaundice  
  • Brain—Confusion, lethargy, difficulty walking, extreme drowsiness, seizures and coma  


The classic features that may lead your doctor to suspect Rocky Mountain spotted fever are high fever, rash, headache, and a history of tick exposure, such as walking in a tick-infested area, within 14 days of developing the symptoms of Rocky Mountain spotted fever. Only about 60% of patients recall being bitten by a tick.  

The early symptoms of Rocky Mountain spotted fever are not specific, and diagnostic tests often are negative early in the disease. Therefore, if your doctor suspects that you have Rocky Mountain spotted fever, he or she generally will begin treatment immediately, even if your blood tests are negative. Early treatment is essential to help you avoid severe complications. Your doctor also may remove a small piece of skin from the area of the rash so it can be examined in a laboratory. This procedure is called a biopsy. The biopsy sample can be tested in the laboratory with chemicals to confirm the presence of Rocky Mountain spotted fever bacteria. Blood tests can confirm the diagnosis, but only two to three weeks after the onset of infection. There are no specific abnormalities on blood tests that indicate an active infection early on.  

Expected Duration

Symptoms of Rocky Mountain spotted fever begin 2 to 14 days after a bite by an infected tick. Most cases of Rocky Mountain spotted fever respond to appropriate antibiotic treatment within a week. Once symptoms develop, a person can die within 2 weeks without proper treatment. 


Because there is no vaccine against Rocky Mountain spotted fever, the most effective way to prevent the illness is to avoid walking in wooded areas or fields where ticks are found. If you must walk in tick-infested areas, follow these precautions: 

  • Wear light-colored clothing, which allows you to promptly identify a clinging tick.  
  • Wear long-sleeved shirts and pants that are snug around the wrists and ankles.  
  • While you are outdoors, check yourself for ticks every two hours.  
  • Use an approved tick repellent.  
  • If you find a tick on your body, remove it immediately with tweezers, then wash your hands thoroughly.  


Rocky Mountain spotted fever is treated with one of the tetracycline drugs, usually doxycycline (sold as a generic), in adults and children over age 9. In general, tetracyclines should not be prescribed for pregnant women and children under the age of 9 because these antibiotics can permanently stain the teeth. However, doxycycline is the best available antibiotic to treat this potentially life threatening infection and is preferred if Rocky Mountain spotted fever is the likely diagnosis, despite the teeth staining. Chloramphenicol (Chloromycetin) is another antibiotic that attacks the bacteria, but it appears to be less effective than doxycycline and is only recommended when doxycycline cannot be given due to allergy or other reaction.   

Most people are cured after taking the antibiotics for five to seven days. Patients may need to be hospitalized if there is severe lung damage, kidney failure, significant bleeding or severe brain involvement. In cases of respiratory failure, mechanical ventilation (treatment with a machine that breathes for the patient) may be necessary. Patients with kidney failure may require dialysis. Those with severe bleeding may need blood transfusions.

When To Call a Professional

Call your doctor immediately if you develop fever, headaches and nausea, with or without a rash, after you have been bitten by a tick. Even if you don't remember being bitten, call your doctor if you develop these symptoms and you have walked recently in tick-infested areas. 


Before effective antibiotics were available, 20% to 25% of people with Rocky Mountain spotted fever died. Now, however, less than 5% of patients die from this illness. Older patients have a slightly higher risk of death than younger ones, and males have a higher risk than females. 

Additional Info

Centers for Disease Control and Prevention (CDC)

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.