Rocky Mountain spotted fever
Rocky Mountain spotted fever is the most common and most severe spotted fever rickettsiosis in the United States, caused by Rickettsia rickettsii and transmitted by the dog tick. The hallmark petechial rash typically lags days behind fever onset, so empiric doxycycline must be started on clinical suspicion alone, since treatment delay drives the disease's disproportionate mortality.
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What this article covers
- Overview
The most common and most severe spotted fever rickettsiosis in the United States: Rocky Mountain spotted fever (RMSF) is caused by Rickettsia rickettsii and transmitted by the dog tick and other…
- Epidemiology
Geographic concentration in a band from the mid-Atlantic to the south-central United States: RMSF has been reported throughout the continental United States but occurs most frequently in a linear…
- Risk factors
Tick exposure in an endemic region, particularly the American dog tick, brown dog tick, or Rocky Mountain wood tick, which serve as vectors throughout the United States.
- Pathophysiology
Tick-transmitted intracellular infection of vascular endothelium: Rickettsia rickettsii is inoculated through a tick bite and invades vascular endothelial cells throughout the body, distinguishing…
- Clinical features
Nonspecific febrile prodrome is the earliest and most consistent finding: fever, headache, malaise, myalgia, and arthralgia appear first and are indistinguishable from ehrlichiosis, anaplasmosis, and…
- Differential diagnosis
Ehrlichiosis and anaplasmosis: near-identical prodrome of fever, headache, and myalgias from tick-borne pathogens; discriminated by vector (Lone Star tick for ehrlichiosis, blacklegged deer tick for…
- Diagnosis
RMSF and the spotted fever rickettsioses are diagnosed on clinical grounds and treated empirically; confirmatory testing is retrospective, not immediate: the diagnosis is established by a compatible…
- Management
Start doxycycline empirically the moment RMSF or another spotted fever rickettsiosis is clinically suspected, without waiting for laboratory confirmation, because delayed treatment is directly…
- Complications
Meningoencephalitis: develops in up to 30% of patients and can cause lasting neurologic sequelae if treatment is delayed.
- Prognosis
Untreated RMSF carries 5% to 10% mortality, among the highest of the tick-borne rickettsial illnesses in the United States.
- Prevention
Avoid tick-infested habitats during peak tick season in endemic regions (the mid-Atlantic to south-central United States, particularly Arkansas, Missouri, North Carolina, Oklahoma, and Tennessee).
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