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Key Features

  • Caused by Rickettsia rickettsii, a parasite of ticks, transmitted by tick bites

  • Most cases occur in only five states: North Carolina, South Carolina, Tennessee, Oklahoma, and Arkansas

  • Most cases occur in late spring and summer

  • Typical incubation period is 2–14 days (median, 7 days)

Clinical Findings

  • Initial symptoms include fevers, chills, headache, nausea and vomiting

  • Cough and pneumonitis often occur early in the disease

  • In more severe cases, delirium, lethargy, seizures, stupor, and coma may also appear

  • Rash (not always found) begins as a faint macule that progresses to large maculopapules and often petechiae

  • Rash begins on the wrists and ankles, characteristically involves palms and soles, and spreads to arms, legs, and trunk

  • Splenomegaly, hepatomegaly, jaundice, myocarditis (which may mimic an acute coronary syndrome), adrenal hemorrhage, polyarticular arthritis, or uremia are occasionally present

  • About 3–5% of recognized cases in the United States are fatal

Diagnosis

  • Thrombocytopenia

  • Hyponatremia

  • Hepatitis

  • CSF low glucose

  • Immunohistologic staining for R rickettsii in skin biopsy specimens and serologic testing are the keys to a definitive diagnosis

Treatment

  • Doxycycline or chloramphenicol (where available) are usually highly effective

  • Prevention: protective clothing and avoiding tick bites

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