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Tickborne Diseases

Rickettsia parkeri Rickettsiosis

Agent

Rickettsia parkeri

Scabbed region at the site of a tick bite called an eschar

R. parkeri is closely related to R. rickettsii, the causative agent of Rocky Mountain spotted fever (RMSF). R. parkeri rickettsiosis and RMSF have similar signs and symptoms, including fever, headache, and rash, but also typically include the appearance of an inoculation eschar (seen at right) at the site of tick attachment. Eschar is not common in cases of RMSF.

Where Found

R. parkeri rickettsiosis is transmitted by Gulf Coast ticks in the southeastern and mid-Atlantic states, as well as parts of southern Arizona.

Incubation Period

2–10 days

Signs and Symptoms

R. parkeri rickettsiosis is characteristically less severe than RMSF and almost always associated with an inoculation eschar (ulcerated, necrotic lesion) at the site of tick attachment. Several days after an eschar appears, the following can develop:

  • Fever
  • Headache
  • Rash (sparse maculopapular or papulovesicular eruptions on the trunk and extremities)
  • Muscle aches

NOTE: R. parkeri rickettsiosis can be difficult to distinguish from RMSF and other spotted fevers, especially during early stages of these diseases. Eschars are uncommonly identified in persons with RMSF.

General Laboratory Findings

  • Mildly elevated hepatic transaminases
  • Mild leukopenia
  • Mild thrombocytopenia, less common
Warning symbol

CONFIRMATION OF THE DIAGNOSIS IS BASED ON LABORATORY TESTING, BUT ANTIBIOTIC THERAPY SHOULD NOT BE DELAYED IN A PATIENT WITH A SUGGESTIVE CLINICAL PRESENTATION.

Laboratory Diagnosis

  • Detection of rickettsial DNA by PCR in eschar swab, whole blood, or skin biopsy.
  • Demonstration of a four-fold change (typically rise) in IgG-specific antibody titer by indirect immunofluorescence antibody (IFA) assay in paired serum samples. The first sample should be taken within the first week of illness and the second should be taken 2 to 4 weeks later.

NOTE: Species-level testing for R. parkeri is not commercially available. RMSF antibody tests are available commercially and often cross-react.

NOTE: IgM antibodies are less specific than IgG antibodies and are more likely to generate false positives. IgM results alone should not be used for laboratory diagnosis.

NOTE: Acute antibody results cannot independently be relied upon for confirmation.

Treatment

See Rocky Mountain spotted fever treatment.

References

Centers for Disease Control and Prevention. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever and other spotted fever group rickettsioses, ehrlichioses, and anaplasmosis—United States: a practical guide for health care and public health professionals. MMWR 2016;65 (No.RR-2).

Paddock CD, Finley RW, Wright CS, et al. Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever. Clin Infect Dis 2008;47:1188-96.

Paddock CD, Goddard J. The evolving medical and veterinary importance of the Gulf Coast tick (Acari: Ixodidae). J Med Entomol 2015;52:230–52.

Straily A, Feldpausch A, Ulbrich C, et al. Notes from the Field: Rickettsia parkeri rickettsiosis—Georgia, 2012–2014. MMWR Morb Mortal Wkly Rep 2016;65:718-719.

Herrick KL, Pena SA, Yaglom HD, et al. Rickettsia parkeri rickettsiosis, Arizona, USA. Emerg Infect Dis 2016;22:780-785.

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