Rocky Mountain Spotted Fever

Rocky Mountain Spotted Fever

Description, Causes and Risk Factors:

ICD-10: A77.0

Abbreviation: RMSF.

Alternative: Blue disease, black fever, blue fever, Mexican spotted fever, São Paulo fever, Tobia fever, black measles.

An acute infectious disease of high mortality, characterized by frontal and occipital headache, intense lumbar pain, malaise, a moderately high continuous fever, and a rash on wrists, palms, ankles, and soles from the second to the fifth day, later spreading to all parts of the body; it occurs in the spring of the year primarily in the southeastern U.S. and the Rocky Mountain region, although it is also endemic elsewhere in the U.S., in parts of Canada, in Mexico, and in South America; the pathogenic organism is Rickettsia rickettsii, transmitted by two or more tick species of the genus Dermacentor; in the U.S. it is spread by D. andersoni in the western states and D. variabilis (a dog tick) in the eastern states.

The incubation period in humans is 2 to 14 days, with an average incubation period of approximately seven days.

RMSF is caused by the bacterium known as Rickettsia ricketsii (a bacterial species, the agent of Rocky Mountain spotted fever, South African tick-bite fever, São Paulo exanthematic typhus of Brazil, Tobia fever of Colombia, and spotted fevers of Minas Gerais and Mexico; transmitted by infected ixodid ticks, especially Dermacentor andersoni and D. variabilis).

You can get RMSF from the bite of an infected tick. In the United States, the American dog tick and the Rocky Mountain wood tick are the main carriers of RMSF bacteria.

The wood tick is found mainly in the Rocky Mountain States, including Montana, Idaho, Colorado, Wyoming, Utah, and Nevada. The dog tick is found from the Great Plains to the East Coast, in Alaska and Hawaii, and in parts of California. The dog tick is not found in the interior northwest.

Though U.S. healthcare providers typically report about 250 to 1,200 cases of RMSF each year to the Centers for Disease Control and Prevention, a record 2,563 cases were reported in 2008.

RMSF is found throughout the United States from April through September. More than half of all cases occur in the mid-Atlantic to southern area of the United States (Delaware, Maryland, Washington, D.C., Virginia, West Virginia, North Carolina, South Carolina, Georgia, Oklahoma, and Florida). North Carolina, Missouri, and Oklahoma report the greatest number of people with RMSF. Although the disease was first discovered in the Rocky Mountains, the area has relatively few cases today.

The disease also has been found in Canada and in Central and South America.


The symptoms of RMSF may include:

    Moderate to high fever, which can persist for 2 to 3 weeks if the infection is untreated.

  • Nausea.

  • Vomiting.

  • Severe headache.

  • Deep muscle pain.

  • Significant tiredness.

  • Chills.

  • Lack of appetite.


There is no widely available laboratory test that canrapidly diagnose Rocky Mountain spotted fever; therefore,testing is often used for con?rmation rather than diagnosis.Treatment decisions are typically based on the symptoms,history and routine clinical laboratory ?ndings.Serology is most often used for con?rmation; a fourfoldrise in titer between the acute and convalescent samplesconsidered to be diagnostic. The most commonly used test isthe indirect immuno?uorescence assay (IFA). An ELISA (enzyme-linked immunosorbent assay) testhas been recently introduced. Other serologic tests includeindirect hemagglutination, latex agglutination, complement?xation and microagglutination. The Weil-Felix test, basedon cross-reactive antigens of Proteus vulgaris, is nonspeci?cand insensitive and has generally been abandoned. Antibodies do not usually appear until 6 to 10 days after the ?rstclinical signs.

Direct immuno?uorescence or immunoperoxidasestaining of a skin biopsy from the rash can sometimes detectR. rickettsii; however, the organisms are focally distributedand may not be found. Immunostaining can also be used ona variety of tissues at autopsy. PCR is also available.Rickettsiae are fastidious and hazardous; therefore,isolation and identi?cation is not widely available. R. rickettsii may be isolated from the blood during the ?rst weekof fever, in cell cultures or by animal inoculation into maleguinea pigs or embryonated eggs.


Treatment is most effective in the early stages of the disease, and is initiated without waiting for disease con?rmation. Patients treated within the ?rst 4-5 days often respond quickly to tetracycline antibiotics such as doxycycline; severely ill patients may take longer to respond and require long term treatment. Chloramphenicol may also be used in some situations.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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