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Essentials of Diagnosis

  • Eschar at site of mite bite.
  • Regional lymphadenopathy.
  • Generalized erythematous papulovesicular eruption on the trunk, extremities, and mucous membranes 9-14 days after exposure.
  • Systemic symptoms including chills, fever, myalgias, anorexia, and photophobia.
  • Prediposing factors include urban dwelling in close proximity to house mice.
  • Serology for R rickettsii will cross-react with antibodies to Rickettsia akari.

General Considerations

Rickettsialpox has been reported infrequently in the United States. This disease is a mild, self-limited illness caused by R akari and is transmitted to humans by a house mite. Both the house mouse and house mite are reservoirs for the organism.


Clinical Findings

A painless papule develops 7-14 days after the mite bite. The papule then becomes vesicular, dries, crusts over, and evolves into a black eschar. The onset of clinical illness, characterized by abrupt onset of high fever, sweats, headache, myalgias, and malaise, occurs 4-7 days after the appearance of the initial papule. The systemic symptoms are usually mild, but, if untreated, the patient will have daily temperature elevations up to 39-39.5°C for 7-10 days.

A maculopapular rash appears at the onset of fever and quickly becomes vesicular. The vesicles are small and nonpruritic, and they may be numerous or few. Within a week, the vesicles crust over and disappear with no sequelae. The diagnosis is best established by the epidemiologic history, the presence of a primary eschar, and a serum IFA test. Therapy with doxycycline or chloramphenicol is effective (see Treatment section for Rocky Mountain spotted fever). Preventive steps involve eliminating house mice and their mites.

rickettsialpox rickettsia akari mite

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