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Rocky Mountain Spotted Fever

RMSF, Spotted Fevers

What is RMSF?

Rocky Mountain spotted fever is an infectious disease caused by a Rickettsia (microorganism similar to a bacteria) and is characterized by fever, head and muscle aches, and skin rash. Spread by the bite of an infected tick, the bite is usually painless and frequently goes unnoticed. Infection can also occur by exposure to infected ticks during removal of the ticks from another person or animal. The majority of cases occur in southeastern US. Most of the nearly 1,000 cases reported each year occur between May and September.

How is it diagnosed?

History: Individuals may report a tick bite or travel to an endemic area. Symptoms appearing about a week after the tick bite include mild fever, headache, and loss of appetite. In some cases, severe symptoms can come on suddenly including high fever, muscle pain, severe headache, nausea and vomiting, restlessness, insomnia, and irritability. Two to six days following the onset of symptoms, small pink spots appear on the wrists and ankles. The non-tender rash then spreads to the palms of the hands and soles of the feet, before spreading over the rest of the body. The rash progresses to become petechiae (dark, bruise-like areas caused by bleeding from small blood vessels under the skin).

Physical exam may reveal fever, cough, and the characteristic rash. Palpation (exam done by pressing with hands on the abdomen) may reveal an enlarged spleen (and occasionally liver), and abdominal tenderness. In severe cases, the individual may look very ill. Lethargy (drowsy, sluggishness), delirium (state of mental confusion and disorientation), stupor, seizures, and coma may occur.

Tests: Before the rash appears, Rocky Mountain spotted fever resembles several other infections, making diagnosis very difficult. Serum chemistries and a complete blood count (CBC) may be done to rule out other conditions such as thrombocytopenia. During the acute phase of the illness, diagnosis can be made by isolating the Rickettsiae in skin biopsy specimens. By the second week, a rise in antibody titer can be detected by specific complement fixation test, immunofluorescent antibody, and microscopic agglutination tests. Laboratory confirmation is made through the use of immunofluorescent antibody (IFA), latex agglutination, or complement fixation.

How is it treated?

Treatment is with oral or intravenous antibiotic drug therapy.



What might complicate it?

Complications may include pneumonia, heart, lung or kidney failure, hemorrhage, inflammation of the heart (myocarditis), pulmonary edema, tissue death (gangrene), vascular damage to brain, lungs, or heart, and swelling or inflammation of the optic nerve where it enters the eyeball (papilledema).

Predicted outcome

With proper treatment, the illness usually subsides after about two weeks. Recovery is usually complete. In untreated cases, especially those marked by extremely high fever, death may follow pneumonia or heart failure.


Conditions with similar symptoms include measles, typhoid fever, meningococcemia, toxic shock syndrome, relapsing fever, rubella, secondary syphilis, leptospirosis, idiopathic thrombocytopenia purpura (ITP) or thrombotic thrombocytopenia, and infectious mononucleosis.

Appropriate specialists

Internist, infectious disease specialist and dermatologist.

Last updated 6 April 2018