Rocky Mountain spotted fever (RMSF) is a severe tick-borne infection
The disease is caused by Rickettsia rickettsii and is transmitted by multiple tick species including the American dog tick, Rocky Mountain wood tick, and brown dog tick.1 Rickettsia rickettsii is considered endemic in certain regions of Canada,2 but human cases of RMSF are rare.
Recognition depends on clinical presentation and history of exposure
Symptoms typically appear 2 to 14 days after a tick bite and include fever, headache, myalgia, and gastrointestinal complaints. The hallmark maculopapular rash usually appears 2 to 5 days after fever onset, initially on the wrists and ankles and spreading centrally, but is absent in 9% to 12% of cases.3 Recent outdoor activity (e.g., hiking, camping, gardening) in endemic areas should raise suspicion for tick exposure. Thrombocytopenia, hyponatremia, and elevated liver enzymes also support the diagnosis.3,4
Awaiting test results should not delay treatment
When RMSF is suspected, testing at a public health laboratory should include RMSF antibody (immunoglobulin G) on serum and polymerase chain reaction on blood or skin biopsy.4 However, patients should be treated empirically when RSMF is suspected.
Doxycycline is the treatment of choice
Prophylactic doxycycline does not prevent RMSF. When RMSF is suspected, doxycycline should be started immediately (100 mg orally twice daily) for 5 to 7 days or at least 3 days after fever resolves.3
Severe cases are common and warrant hospital care and public health notification
In a study of 46 people with RMSF, 57% required hospital admission for severe manifestations, including encephalitis, respiratory failure, acute kidney injury, or hepatic dysfunction. Patients admitted to hospital should receive supportive care and doxycycline (100 mg oral or intravenous twice daily).3 Infectious diseases consultation and public health notification are recommended for surveillance, with tick and animal monitoring to characterize the regional epidemiology of R. rickettsii.4,5
See related commentary at www.cmaj.ca/lookup/doi/10.1503/cmaj.260668
Footnotes
Competing interests: Robert Kozak reports receiving grant funding from the Canadian Institutes of Health Research (CIHR). Isaac Bogoch reports receiving peer-reviewed research grants from CIHR for emerging infectious diseases and HIV prevention, and consults for the Weapons Threat Reduction Program at Global Affairs Canada. No other competing interests were declared.
This article has been peer reviewed.
References
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