A 5-year-old febrile boy with nausea, vomiting and fatigue develops a red, blotchy rash that blanches with pressure on his wrists, ankles and forearms about a week after returning from a camping trip with his family in the southeastern United States.
Within 24 hours the rash spreads to his palms and soles and then up his arms and thighs to the trunk and face. What’s your diagnosis?
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Rocky Mountain spotted fever (RMSF) is a bacterial infection caused by Rickettsia rickettsii and transmitted to humans via bites from ticks and fleas, or from healing bite contaminated by lice and/or flea feces. Vectors vary depending on geographic region and include the brown dog tick, Rhipicephalus sanguineus, common in the southern United States; the wood tick, Dermacentor andersoni, which is common in the western United States; and the dog tick, D. variabilis, found mostly in the eastern United States.
The course of disease can range from asymptomatic to fulminant. If treated promptly, illness is fairly mild, but the disease can progress rapidly if ignored – fatality rates in untreated cases range from 20% to 80%.
Infection incidence is seasonal and corresponds with tick activity and human exposure, peaking in the early summer. Incidence is particularly high among children in the eastern United States, and men in mountainous areas of Montana and other western states.
Initial RMSF signs and symptoms are often abrupt, nonspecific and mimic other diseases. After a three to 12 day incubation period following the time of exposure, patients may develop the following symptoms: high fever, chills, severe headache, photosensitivity, nausea, vomiting, abdominal pain, loss of appetite and fatigue.
The characteristic rash generally appears on the fourth day of fever, and appears first on the wrists, ankles and forearms, spreading to the palms and soles and then the arms, thighs, trunk and face within 6 to 18 hours. The rash becomes macular and papular, and turns a deeper shade of red after one to three days. Between days two to four, petechiae appear on the rash, and it no longer blanches on pressure.
Infection severity can be determined by the extent and progression of the rash — areas of gangrene may appear on a patient’s toes, fingers, earlobes, nose, scrotum or vulva. Alternately, it may be harder to recognize the rash in patients with darker pigmented skin, but the course of illness may be no less severe. If left untreated, the infection can spread to the bloodstream to other areas of the body, causing heart, lung or kidney failure; meningitis; brain damage; gangrene; and shock.
Clinicians usually diagnose RMSF by evaluating a patient’s signs and symptoms, conducting a physical exam and obtaining a blood sample, rash specimen or the tick, when available, for the presence of the organism.
Treatment & Prevention
Early treatment with an effective antibiotic such as doxycycline, tetracycline, or chloramphenicol for pregnant patients, is key with RMSF — survival rates increase exponentially if patients are treated within five days of symptom onset.
Advise patients to take precautions to prevent tick bites when spending time in tick-infested areas, such as wooded and grassy areas. This includes wearing light colored clothing to make it easier to find ticks; tucking in clothes; pulling back hair; applying an insect repellent that contains DEET (N,N-diethyl-meta-toluamide); and inspecting the body for ticks at the end of the day.
If a tick is found it should be removed with tweezers, taking care not to burst or twist the tick, and placed in a plastic bag in the freezer for testing in the event of illness. Ticks that are removed within 36 hours pose minimal risk for disease transmission, according to the National Institute of Allergy and Infectious Diseases.
3. Freedberg IM, Isin AZ, Wolff K, et al. Fitzpatrick’s Dermatology in General Medicine (5th ed.). 1999. New York: McGraw-Hill.