ROCKY MOUNTAIN SPOTTED FEVER

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%.

Clinical

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

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.

Treatment

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.

References

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