Rocky Mountain Spotted Fever

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Map of geographic distribution of RMS incidence in 2010; cases per millions. Not notifiable in Alaska and Hawaii. 0 in: NV, SD, NE, WV, VT, MA. 0.2 – 1.5 in WA, OR, CA, UT, CO, NM, TX, ND, MN, WI, MI, OH, PA, LI, FL, LA, KY. 1.9 – 19 in ID, MT, WY, NE, IA, IL, IN, AZ, MS, AL, GA, SC, VA, DC. 19 – 63 in OK, MO, AR, TN, NC
In the US, Rocky Mountain spotted fever is most prevalent in the southeastern states. (credit: modification of work by Centers for Disease Control and Prevention)

OpenStax Microbiology

The disease Rocky Mountain spotted fever (RMSF) is caused by Rickettsia rickettsii and is transmitted by the bite of a hard-bodied tick such as the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (D. andersoni), or brown dog tick (Rhipicephalus sanguineus).

This disease is endemic in North and South America and its incidence is coincident with the arthropod vector range. Despite its name, most cases in the US do not occur in the Rocky Mountain region but in the Southeast; North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri account for greater than 60% of all cases.

Signs and symptoms of RMSF include a high fever, headache, body aches, nausea, and vomiting. A petechial rash (similar in appearance to measles) begins on the hands and wrists, and spreads to the trunk, face, and extremities. If untreated, RMSF is a serious illness that can be fatal in the first 8 days even in otherwise healthy patients. Ideally, treatment should begin before petechiae develop, because this is a sign of progression to severe disease; however, the rash usually does not appear until day 6 or later after onset of symptoms and only occurs in 35%–60% of patients with the infection. Increased vascular permeability associated with petechiae formation can result in fatality rates of 3% or greater, even in the presence of clinical support. Most deaths are due to hypotension and cardiac arrest or from ischemia following blood coagulation.

Diagnosis can be challenging because the disease mimics several other diseases that are more prevalent. The diagnosis of RMSF is made based on symptoms, fluorescent antibody staining of a biopsy specimen from the rash, PCR for Rickettsia rickettsii, and acute and convalescent serologic testing. Primary treatment is doxycycline, with chloramphenicol  as the second choice.

Photo of many red spots on a person’s hand.
Rocky Mountain spotted fever causes a petechial rash. Unlike epidemic or murine typhus, the rash begins at the hands and wrists and then spreads to the trunk. (credit: modification of work by Centers for Disease Control and Prevention)

Source:

Parker, N., Schneegurt, M., Thi Tu, A.-H., Forster, B. M., & Lister, P. (n.d.). Microbiology. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/microbiology


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