Rickettsia parkeri: Eschar diagnosis
Authors: Nadine M. Kaskas, Johnathan J. Ledet, Alexander Wong, Christina A. Muzny, Latesha Elopre, Lauren Hughey
Journal: Journal of the American Academy of Dermatology (2014)

To the Editor: A 30-year-old Caucasian woman presented to the emergency department in June with a 5-day history of flu-like symptoms. She denied recent travel from her residence, Columbiana, Alabama. She was in her usual state of health until she experienced a tick bite on her forearm 7 days before admission. Following tick removal, she noticed fatigue, myalgias, arthralgias, and severe headache, with retro-orbital pain. A temperature up to 105°F recalcitrant to antipyretics accompanied her symptoms. On examination, the patient was febrile with a temperature of 105.7°F. Although she was hemodynamically stable, notable laboratory results included thrombocytopenia (platelets: 133,000 109/L). No maculopapular rash was noted. An ulcerated nodule with a central eschar was noted on her right forearm (Fig 1). The eschar was biopsied by punch technique with half of the specimen processed routinely, while the other half was snap frozen in liquid nitrogen and sent to the Centers for Disease Control and Prevention (CDC) for further study. Histopathologic section study demonstrated a marked lymphocytic vasculitis with associated ulcer and dermal necrosis (Fig 2). Polymerase chain reaction (PCR)-based testing performed at the CDC was positive for spotted fever group rickettsiae. Gene sequencing confirmed presence of Rickettsia parkeri.Fig 2Rickettsia parkeri infection. Histopathology of cutaneous punch biopsy of eschar. A nodular and diffuse lymphoid infiltrate permeates the superficial and deep dermis and extends focally into the subcutaneous fat. There is overlying ulcer and crust with associated necrosis extending to the mid dermis. (Hematoxylin-eosin stain; original magnification: ×20.) Inset: Small to medium sized vessel with lymphocytic vasculitis showing endothelial swelling and fibrin thrombi (arrowhead) and perineural inflammation (arrow). (Hematoxylin-eosin stain; original magnification: ×200.)View Large Image Figure ViewerDownload Hi-res image Download (PPT) The patient's blood cultures were negative, as was serologic study for Borrelia burgdorferi and Ehrlichia chaffeensis antibodies. No serologic tests for rickettsial organisms were obtained by primary team. Treatment in the emergency department included fluids and doxycycline. She was afebrile after 3 days on doxycycline and was discharged home with a 17-day course of doxycycline. She recovered without sequelae. Rickettsia parkeri is a spotted fever group rickettsia first documented in 2004 to cause human infection.1Myers T. Lalani T. Dent M. Jiang J. Daly P.L. Maguire J.D. et al.Detecting Rickettsia parkeri infection from eschar swab specimens.Emerg Infect Dis. 2013; 19: 778-780Crossref PubMed Scopus (31) Google Scholar, 2Paddock C.D. Fournier P.E. Sumner J.W. Goddard J. Elshenawy Y. Metcalfe M.G. et al.Isolation of Rickettsia parkeri and identification of a novel spotted fever group Rickettsia sp from Gulf Coast ticks (Amblyomma maculatum) in the United States.Appl Environ Microbiol. 2010; 76: 2689-2696Crossref PubMed Scopus (98) Google Scholar, 3Paddock C.D. Sumner J.W. Comer J.A. Zaki S.R. Goldsmith C.S. Goddard J. et al.Rickettsia parkeri: a newly recognized cause of spotted fever rickettsiosis in the United States.Clin Infect Dis. 2004; 38: 805-811Crossref PubMed Scopus (388) Google Scholar Rickettsia parkeri infections in the United States and South America are a clinical rarity, with 27 cases having been reported in the English literature.1Myers T. Lalani T. Dent M. Jiang J. Daly P.L. Maguire J.D. et al.Detecting Rickettsia parkeri infection from eschar swab specimens.Emerg Infect Dis. 2013; 19: 778-780Crossref PubMed Scopus (31) Google Scholar, 4Romer Y. Seijo A.C. Crudo F. Nicholson W.L. Varela-Stokes A. Lash R.R. et al.Rickettsia parkeri rickettsiosis, Argentina.Emerg Infect Dis. 2011; 17: 1169-1173Crossref PubMed Scopus (85) Google Scholar Other spotted fever group rickettsiae include Rickettsia felis, Rickettsia 364D, and Rickettsia massiliae. Documented cases reveal a disease that is milder than classically described Rocky Mountain spotted fever: typical symptoms include local lymphadenopathy, fever, headache, myalgias, inoculation eschar, and a maculopapular exanthem.5Paddock C.D. Finley R.W. Wright C.S. Robinson H.N. Schrodt B.J. Lane C.C. et al.Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.Clin Infect Dis. 2008; 47: 1188-1196Crossref PubMed Scopus (209) Google Scholar While patients with Rocky Mountain spotted fever rarely present with eschars, R. parkeri has been confused with Rickettsia akari, a mite-borne causative agent of eschar-associated rickettsialpox. Even though most American cases of rickettsialpox have occurred in inner city areas of northeastern states, recent cases have been reported in areas endemic to R. parkeri, such as rural North Carolina.5Paddock C.D. Finley R.W. Wright C.S. Robinson H.N. Schrodt B.J. Lane C.C. et al.Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.Clin Infect Dis. 2008; 47: 1188-1196Crossref PubMed Scopus (209) Google Scholar Once the broad differential diagnosis of the febrile patient presenting with eschar has been narrowed down to the spotted fever group, diagnostic difficulty remains in obtaining a species-specific diagnosis. In traditional serologic assays, antibodies generated to R. parkeri antigens can cross-react with those of R. rickettsia and R. akari.5Paddock C.D. Finley R.W. Wright C.S. Robinson H.N. Schrodt B.J. Lane C.C. et al.Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.Clin Infect Dis. 2008; 47: 1188-1196Crossref PubMed Scopus (209) Google Scholar While serology can define a diagnosis in select cases, an accurate species-specific diagnosis can be made by sending fresh skin biopsy specimens of the eschar and rash lesions to an appropriate reference laboratory for PCR or culture-based assays.1Myers T. Lalani T. Dent M. Jiang J. Daly P.L. Maguire J.D. et al.Detecting Rickettsia parkeri infection from eschar swab specimens.Emerg Infect Dis. 2013; 19: 778-780Crossref PubMed Scopus (31) Google Scholar, 5Paddock C.D. Finley R.W. Wright C.S. Robinson H.N. Schrodt B.J. Lane C.C. et al.Rickettsia parkeri rickettsiosis and its clinical distinction from Rocky Mountain spotted fever.Clin Infect Dis. 2008; 47: 1188-1196Crossref PubMed Scopus (209) Google Scholar Based on the literature, we suggest quantitative real-time PCR targeting the R. parkeri species-specific Rpark using DNA extracted from eschar specimens to be the gold standard for diagnosis.1Myers T. Lalani T. Dent M. Jiang J. Daly P.L. Maguire J.D. et al.Detecting Rickettsia parkeri infection from eschar swab specimens.Emerg Infect Dis. 2013; 19: 778-780Crossref PubMed Scopus (31) Google Scholar, 2Paddock C.D. Fournier P.E. Sumner J.W. Goddard J. Elshenawy Y. Metcalfe M.G. et al.Isolation of Rickettsia parkeri and identification of a novel spotted fever group Rickettsia sp from Gulf Coast ticks (Amblyomma maculatum) in the United States.Appl Environ Microbiol. 2010; 76: 2689-2696Crossref PubMed Scopus (98) Google Scholar We are indebted to the University of Alabama at Birmingham Department of Medicine, Division of Infectious Diseases, and Department of Dermatology for their administrative support.