Rocky Mountain Spotted Fever

Rocky Mountain spotted fever (RMSF) is one of the most dangerous tick-borne illnesses in the United States. It happens when bacteria called Rickettsia rickettsii enter the body through a tick bite.

It gets its name from the trademark rash it causes. The illness also causes a headache, chills and muscle pain. It can be fatal without treatment.


Rocky Mountain spotted fever (RMSF) is a tick-borne disease caused by bacteria called Rickettsia rickettsii. It is spread through the bite of an infected tick and typically occurs in spring thru mid-summer. Symptoms start with a sudden, high fever around 102 to 103 degrees Fahrenheit, severe headache, fatigue, muscle aches and chills. RMSF can be fatal and is the most serious tick-borne illness in the United States.

RMSF gets its name from the trademark rash that appears during and after the fever. It consists of small red splotches or spots that begin on the wrists and ankles and move up the arms, legs and torso toward the trunk. The rash also can appear on the soles of the feet and palms of the hands. Without treatment, RMSF can cause severe complications including sepsis. With prompt antibiotics, most people make a full recovery. Tetracycline drugs, such as doxycycline (also sold as a generic) are usually prescribed for RMSF in adults and children over age 9 because they attack the bacteria best. Chloramphenicol, which is less effective, may be used in children younger than 9 if doxycycline cannot be given due to allergy or intolerance.


Symptoms usually start within two days to two weeks after an infected tick bite. They include fever, severe headache, chills, extreme fatigue (prostration), muscle pain and a rash that may begin on the wrists and ankles or spread to other parts of the body.

RMSF symptoms can be hard to recognize because they are similar to those of other, more common diseases. Early treatment with antibiotics reduces the death rate from about 20 percent to 5 percent.

Your doctor can diagnose RMSF by taking a blood sample to look for antibodies to the bacteria Rickettsia rickettsii. However, the test won’t show a positive result until several days after your illness begins. In the meantime, doctors will prescribe antibiotics such as doxycycline to prevent complications. The antibiotic works best if it’s taken as soon as possible after the tick bite. The rash that develops in RMSF is typically nonspecific, and some people never get one. Unlike some other tickborne infections, RMSF isn’t contagious and can’t be spread from person to person.


Before the antibiotic era, Rocky Mountain spotted fever was one of the deadliest tick-borne diseases. It still causes serious illness in some people and, in severe cases, can lead to long-term health problems or death if not treated correctly.

The incubation period for RMSF is usually between five and ten days. Many patients present to physicians before the hallmark rash develops, making diagnosis difficult. In addition, blood tests are often negative early in the course of infection.

If a patient presents with the classic symptoms of RMSF, physicians should treat them immediately, without waiting for laboratory test results. Empiric doxycycline treatment significantly reduces mortality and prevents most complications. Although doxycycline belongs to the tetracycline family of drugs, which is not given to children under age 8 because it can stain their teeth, new research indicates that short courses of doxycycline do not cause tooth discoloration. Treatment with doxycycline should be continued for several days after the fever goes away.


The best way to prevent tick-borne diseases, including Rocky Mountain spotted fever, is to practice good tick prevention, such as wearing long sleeves and pants in brushy areas, checking for ticks frequently and removing them promptly with fine-tipped tweezers. You can also use insect repellent and treat clothing with permethrin.

RMSF is caused by the bacteria Rickettsia rickettsii, which spread to people through the bite of infected ticks. These ticks are common in many parts of the United States and are especially active from spring through autumn.

Symptoms of the disease appear within one week after a tick bite, although some cases have been reported much later. The rash, usually on the hands, arms, feet or legs, is a distinctive pattern of flat spots. The fever and rash go away with treatment, but RMSF can cause permanent health problems, such as loss of bowel or bladder control (fecal or urinary incontinence). Without proper care, the disease can be fatal.

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