Rocky Mountain Spotted Fever

Facts you should know about Rocky Mountain spotted fever

Reported incidence of RMSF per million people in 2008
Reported incidence of RMSF per million people in 2008; NN=not reported. SOURCE: CDC.
  • RMSF is a potentially serious tick-borne disease, and it is the most common cause of fatal tick-borne diseases in the United States.
  • The incidence of RMSF has increased from less than two cases per million people in the year 2000 (approximately 500 cases) to over six cases per million people in 2010 (approximately 2,000 cases).
  • Although RMSF cases have been reported throughout the United States, the highest incidence of cases in 2010 were in Arkansas, Delaware, Missouri, North Carolina, Oklahoma, and Tennessee.
  • RMSF is treatable with antibiotics, but it can have serious long-term effects and can potentially lead to death if not treated quickly and properly.

What is Rocky Mountain spotted fever?

Rocky Mountain spotted fever (RMSF) is a tick-borne disease caused by the bacterium Rickettsia rickettsii. This illness, which is found in North, Central, and South America, is transmitted via the bite of an infected tick. The illness affects the lining of blood vessels (causing a condition termed vasculitis), causing the blood vessels to leak, which ultimately can cause damage to nearly all internal organs. It is the most common cause of fatal tick-borne diseases in the United States. The fatality rate is less than 1%.

Where do most cases of RMSF occur in the U.S.?

Cases of RMSF have been reported in many areas of the country, and the disease is not restricted to the Rocky Mountain region, as its name may imply. In fact, Arkansas, Missouri, North Carolina, Oklahoma, and Tennessee account for over 60% of reported cases. In 2010, there were approximately 2,000 cases reported in the U.S., which is more than twice as many cases reported annually in the 1990s.

What causes Rocky Mountain spotted fever?

RMSF is caused by Rickettsia rickettsii, a bacterium that is transmitted to humans via the bite of an infected tick. In the United States, these ticks include the Rocky Mountain wood tick (Dermacentor andersoni), the American dog tick (Dermacentor variabilis), and the brown dog tick (Rhipicephalus sanguineus).

How is Rocky Mountain spotted fever transmitted?

The tick needs to bite humans and then attach itself for at least six to 10 hours for the transmission of the bacterium to occur, although transmission does not occur for up to 24 hours in some cases.

What are Rocky Mountain spotted fever risk factors?

Being outdoors in areas where the ticks carrying Rickettsia rickettsii are prevalent is the major risk factor for acquiring the disease.

Although the name of the disease includes the Rocky Mountains, it is somewhat of a misnomer as RMSF is most commonly reported in the south Atlantic and south central regions of the United States (though the Rocky Mountain region was one of the first areas where the disease was identified).

The incidence of RMSF increases when ticks are most active and people spend more time outdoors, which commonly occurs during the summer months, with peak periods in June and July. However, RMSF can occur during any month of the year.

Is Rocky Mountain spotted fever contagious?

RMSF is transmitted via a tick bite and cannot be transmitted from person to person. There are rare reports of RMSF being transmitted via blood transfusions, however.

What are Rocky Mountain spotted fever symptoms and signs?

RMSF typically begins with headaches, a high fever, and muscle aches. Some individuals may also develop abdominal pain, nausea, and vomiting. It is frequently followed by a rash (usually two to five days after the onset of fever) that appears around the ankles, forearms, and wrists. The rash consists of small, non-itchy, flat pink spots that then spread to the individual's chest and back and then down the remainder of the extremities. The rash can sometimes involve the palms and soles. In some cases (about 10% of the time), no rash develops, which makes diagnosing RMSF much more difficult. In about 35%-60% of patients with RMSF, a spotty rash that is red or purple (petechiae) may develop around the sixth day or later after the onset of symptoms. The appearance of this type of rash indicates that the disease has become more severe.

The damage to the lining of small blood vessels causes them to become leaky, with bleeding or clot formation leading to the following potential complications:

  • Kidneys: Kidney failure may occur due to damage of the small blood vessels in the kidney.
  • Extremities: Due to damage to the smallest blood vessels in the fingers or toes, blood flow can be disrupted, leading to gangrene, with amputation sometimes being necessary.
  • Brain: Headaches, lethargy, confusion, and even seizures can occur due to damage to the blood vessels in the brain.
  • Heart and lungs: Inflammation of heart tissue (myocarditis) or respiratory failure can lead to death.
  • Eyes: Damage to the eyes may occur, often due to inflammation of the vascular structures of the eye (uveitis or retinal vasculitis).


Rocky Mountain Spotted Fever: See Photos of the Rash See Slideshow

What is the incubation period for Rocky Mountain spotted fever?

The signs and symptoms of RMSF can appear within the first few days after the tick bite, or they can be delayed by up to two weeks. The typical rash usually appears approximately two to five days after the onset of fever, though it may not appear at all.

What specialists treat Rocky Mountain spotted fever?

RMSF is usually initially treated by a primary-care doctor (pediatrician, family doctor, or general internist) or emergency-medicine specialist. Depending on the severity of the illness, an infectious-disease specialist may also be consulted.

How do health care providers diagnose Rocky Mountain spotted fever?

RMSF can be difficult to initially diagnose, as many of the early symptoms (such as headache, body aches, and fever) are commonly seen with many other viral or bacterial infections. The presence of the classic rash usually helps in establishing the diagnosis, however, not all patients with RMSF will develop a rash. A tentative clinical diagnosis of RMSF can be made based on the patient's symptoms and their physical exam, in addition to a history of possible tick exposure. The prompt initiation of treatment in suspected RMSF is crucial, even before confirmatory test results are obtained. Specialized laboratory tests (such as immunofluorescent antibody tests, latex agglutination, or enzyme immunoassays) are available to confirm the diagnosis of RMSF. However, these tests are not readily available in all health care facilities, and results of these tests may take days or weeks.

During infection with RMSF, an individual's immune system will develop antibodies usually within the first seven to 10 days after illness onset (therefore the confirmatory lab tests might be negative during the first week). The indirect immunofluorescent assay needs to be performed on two samples to show a rise in antibody titers (the first sample is usually taken during the first week, and the second sample about two to four weeks later).

Additional routine blood tests, such as a complete blood count, an electrolyte panel, liver function tests, and coagulation studies will be obtained. These blood tests can help monitor for any potential complications, such as kidney failure or problems with blood clotting. An electrocardiogram (ECG) or chest X-ray may also be obtained if there are any potential cardiac or pulmonary manifestations of the disease. In individuals who have confusion or seizures, a CT scan of the brain may also be ordered. Additional tests will depend on the patient's symptoms and the severity of the disease.

What is the treatment for Rocky Mountain spotted fever?

Antibiotics are the treatment for RMSF. Doxycycline is the antibiotic of choice in children and adults suspected of having RMSF. Antibiotic treatment is most effective if started within the first five days of symptom onset, so prompt treatment with antibiotics should be initiated in any individual suspected of having RMSF, even before confirmatory laboratory testing results are available. The early initiation of antibiotics decreases the mortality rate of RMSF from 20% to less than 1%. For individuals who are allergic to doxycycline, and in some pregnant patients, chloramphenicol (Chloromycetin, Econochlor, Ocu-Chlor) is an alternative antibiotic that can be used. Although the disease responds well to treatment, it can become life-threatening if not treated promptly.

Though certain patients with mild symptoms and signs suspected of having RMSF can be treated as outpatients with antibiotics and close follow-up, other patients with suspected RMSF will require admission to the hospital for close monitoring and further evaluation.

What is the prognosis of Rocky Mountain spotted fever?

If diagnosed early and treated promptly, RMSF has a very good prognosis. Most patients will fully recover without any long-term disabilities. However, a delay in diagnosis and treatment is contributory to the higher rates of complications and mortality seen with RMSF. In the United States, the mortality rate for RMSF is currently less than 1%. In the preantibiotic era, the mortality rate was around 30%.

What are the long-term effects of Rocky Mountain spotted fever?

The long-term effects of RMSF depend on the severity of the illness. Many patients recover fully without any long-term effects, whereas other individuals may suffer from permanent long-term neurologic problems and internal organ dysfunction.

Is there a vaccine for Rocky Mountain spotted fever?

There are currently no vaccines available for RMSF. The best way to prevent the disease is to avoid tick bites.

Is it possible to prevent Rocky Mountain spotted fever?

RMSF can be prevented by implementing the following precautionary measures that can help avoid tick bites:

  • Wear long pants and long sleeves when walking or working outside, especially in wooded areas.
  • Use DEET-containing insect repellents.
  • Check yourself, family members, and pets for ticks after you have been outside in a high-risk area.
  • If a tick is found, proper removal of the tick is important. Removal of the tick should be performed with tweezers while wearing gloves. The tick should not be crushed, and care should be taken to ensure that the whole tick is removed while gently pulling the tick out.
  • If possible, keep the tick so that identification of the tick species can be established if necessary.

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Tintinalli, Judith E., et al. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7th ed. New York: McGraw Hill Professional, 2010; 1071-1072.

United States. Centers for Disease Control and Prevention. "Rocky Mountain Spotted Fever (RMSF)." May 7, 2019. <>.