Detecting Rickettsia parkeri Infection from Eschar Swab Specimens

Todd Myers

, Tahaniyat Lalani, Mike Dent, Ju Jiang, Patrick L. Daly, Jason D. Maguire, and Allen L. Richards

Author affiliations: Naval Medical Research Center, Silver Spring, Maryland, USA (T. Myers, J. Jiang, A.L. Richards); Naval Medical Center, Portsmouth, Virginia, USA (T. Lalani, P.L. Daly, J.D. Maguire); Naval Air Station, Pensacola, Florida, USA (M. Dent)

Abstract

The typical clinical presentation of several spotted fever group Rickettsia infections includes eschars. Clinical diagnosis of the condition is usually made by analysis of blood samples. We describe a more sensitive, noninvasive means of obtaining a sample for diagnosis by using an eschar swab specimen from patients infected with Rickettsia parkeri.

Until 2004, all confirmed cases of tick-borne spotted fever in North, Central, and South America were attributed to 1 pathogen, Rickettsia rickettsii, the cause of Rocky Mountain spotted fever. Historically, in the Western Hemisphere, tick-borne rickettsiae other than R. rickettsii were often described as nonpathogens (1).
In 2004, an otherwise healthy US serviceman living in the Tidewater region of eastern Virginia, USA, sought treatment at an acute care clinic with fever, mild headache, malaise, diffuse myalgias and arthralgias, and multiple eschars on his lower extremities. He reported frequent tick and flea exposures but could not recall a specific arthropod bite before illness. However, R. parkeri, a tick-associated Rickettsia species, was subsequently isolated from an eschar biopsy specimen, documenting the first recognized case of R. parkeri rickettsiosis (2,3). In 2006, another US serviceman visited the National Naval Medical Center with similar symptoms. He had recently returned from a vacation in the Virginia Beach area; subsequently, R. parkeri was also isolated from this patient (4). To date, >25 cases of R. parkeri infections have been diagnosed in the United States and South America (5).
R. parkeri was first isolated from Gulf Coast ticks (Amblyomma maculatum) in 1937. The organism remained relatively obscure for the next several decades. R. parkeri is a member of the spotted fever group (SFG) of rickettsiae, which are gram-negative obligate intracellular rod-shaped bacteria transmitted by an arthropod vector. A. maculatum ticks, the vectors for R. parkeri in the United States, have a distribution that extends across all states bordering the Gulf of Mexico and includes several other southern, mid-Atlantic, and central states (6). R. parkeri has been detected in or isolated from A. maculatum ticks in many of these states.