By Gary M. White, MD

Rocky mountain spotted fever (RMSF) is a Rickettsial infection acquired from the bite of a tick--either the American dog tick (Dermacentor variabilis) or the Rocky Mountain wood tick (D. andersoni). The bacterium is Rickettsia rickettsii.

The disease occurs in the Rocky Mountain states of the US, Maryland, Virginia and North Carolina, as well as Mexico and some countries in South America. RMSF occurs most commonly during times of increased tick activity. Incidence is highest in children aged 1-9 years.  Onset is most common during the summer months. If untreated, the case fatality rate is as high as 30%.


Several days (range 3-12) after the tick bite, the patient develops headache, malaise, and fever, followed 3-4 days later by a maculopapular eruption most prominent initially on the wrists and ankles. It may later spread to the limbs, trunk, and face. The rash is often hemorrhagic and may be confluent. Pneumonitis, encephalitis, disseminated intravascular coagulation, and gangrene of the distal extremities may occur.


Diagnosis is based on clinical findings, seasonality and history of tick bite or exposure.   Serologic tests are available, but only serve to confirm the diagnosis after the fact.


Close monitoring of the patient in a hospital setting is recommended. An infectious disease specialist should be consulted. In the past, doxycycline, e.g., 100 mg BID for adults, has been the treatment of choice. For pregnant women and children under 8, chloramphenicol has been recommended.




Homepage | FAQs | Contact Dr. White

It is not the intention of to provide specific medical advice, diagnosis or treatment. only intends to provide users with information regarding various medical conditions for educational purposes and will not provide specific medical advice. Information on is not intended as a substitute for seeking medical treatment and you should always seek the advice of a qualified healthcare provider for diagnosis and for answers to your individual questions. Information contained on should never cause you to disregard professional medical advice or delay seeking treatment. If you live in the United States and believe you are having a medical emergency call 911 immediately.