Rocky Mountain Spotted Fever
Introduction
Rocky Mountain spotted fever (RMSF) is both the most serious and the most commonly reported rickettsial infection in the USA. The causative organism is Rickettsia rickettsii, which is a member of the spotted fever group. R. rickettsii are small, aerobic, obligate intracellular, Gram-negative coccobacilli. The disease name is derived from its origins in the Rocky Mountains. Initially known as “black measles,” RMSF was first recognized in the Snake River Valley of Idaho and the Bitterroot Valley of western Montana in the late 1890s.1, 2 In 1906, a medical team led by Howard Taylor Ricketts determined the role of ticks in disease transmission.3 Today, most cases in the USA occur in the mid-Atlantic and southern states (Fig 1). RMSF also has been found in Canada and in Central and South America. RMSF is a systemic small-vessel vasculitis. Clinical presentations range from benign to life threatening. Early recognition and prompt treatment are keys to reduce mortality from this intriguing illness.
Section snippets
Epidemiology
In the USA, Dermacentor variabilis, the American dog tick, is the predominant vector and reservoir of RMSF, responsible for transmission in the Eastern US. The Rocky Mountain wood tick, Dermacentor andersoni, is the vector in the Western states. Recently, the brown dog tick, Rhipicephalus sanuineus, has been found to transmit RMSF in Arizona and Mexico, an area in which Dermancentor ticks were uncommon and RMSF previously had been thought to be rare or nonexistent. Amblyomma cajennense and
Clinical Presentation
The tick bite is not painful, and it often goes unnoticed. An eschar is rarely seen at the bite site.11 The incubation time for RMSF can range from 2 to 14 days with a median of 7 days. The triad of fever, headache, and rash are the most reliable symptoms. Virtually all patients will develop fever as the first sign of illness, which is usually above 102°F. In addition, headaches, malaise, restlessness, arthralgias, myalgias, conjunctival injection, nonproductive cough, nausea, and vomiting are
Diagnosis
Early diagnosis of RMSF is based on high clinical suspicion in the setting of common symptoms and appropriate epidemiologic risks. Few laboratories are specific for the diagnosis of RMSF. The total while blood cell count can be normal, high, or low. Thrombocytopenia is seen in up to 50% of both mild and severe cases.15 Hyponatremia and elevated liver-associated enzymes may also be seen. Despite vascular damage, derangements in coagulation times and consumption of fibrinogen are not common in
Treatment
The prognosis of RMSF is closely related to the timeliness of appropriate antibiotics. Early treatment of RMSF is crucial for recovery and there are reported case fatality rates of 10% to 25% without early treatment. The decision to treat should be based on clinical suspicion as no available test can confirm the diagnosis early in the disease course. Doxycycline has the best proven efficacy against R. rickettsii and should be started immediately for adults and children. The standard dose for
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Cited by (13)
The Evaluation and Management of Rocky Mountain Spotted Fever in the Emergency Department: a Review of the Literature
2018, Journal of Emergency MedicineCitation Excerpt :The causative bacteria, Rickettsia rickettsii, is a Gram-negative, obligate intracellular bacteria, and infection may result in a systemic small vessel vasculitis ranging from mild to deadly (6–9). The varied clinical presentation and signs and symptoms that overlap with many other clinical conditions can make diagnosis challenging in the emergency department (ED) (2,3,9–12). Delayed diagnosis of this virulent disease may be fatal (6).
Rickettsia rickettsii (rocky mountain spotted fever) attack
2016, Ciottone's Disaster MedicineSyndromic classification of rickettsioses: An approach for clinical practice
2014, International Journal of Infectious DiseasesRickettsial Infections
2014, Encyclopedia of the Neurological SciencesSmuggling across the border: How arthropod-borne pathogens evade and exploit the host defense system of the skin
2014, Journal of Investigative DermatologyRocky Mountain Spotted Fever in Children
2013, Pediatric Clinics of North AmericaCitation Excerpt :The availability of effective antimicrobial agents in the 1950s was associated with a decline in reported cases that seemed to reverse in the 1960s. There seems to be a 30-year to 40-year cycle of disease for reasons that are unclear.1 Between 2000 and 2008, aggregate incidence was 2 to 4 per million among children ages 1 to 19 years old and 6 to 8 per million among adults over 40 years old.7
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