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About the Authors:
Michael L. Levin
* E-mail: [email protected]
Affiliation: Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
Lindsay F. Killmaster
Affiliation: Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
Galina E. Zemtsova
Affiliation: Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
Jana M. Ritter
Affiliation: Infectious Diseases Pathology Branch, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
Gregory Langham
Affiliation: Animal Resources Branch, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
Introduction
Rickettsia rickettsii is a tick-borne pathogen that causes Rocky Mountain spotted fever (RMSF) and Brazilian spotted fever in North, Central, and South America. In the United States, the American dog tick Dermacentor variabilis is one of the primary vectors of this pathogen. Rickettsia spp. seroprevalence in domestic and stray dogs in disease-endemic regions can be high – up to 68–81% [1], [2], and proximity to seropositive dogs is a risk factor for RMSF in humans [3]–[6]. Dogs themselves are susceptible to infection and clinical cases, sometimes fatal, have been described [7]–[14]. Because of their susceptibility to R. rickettsii and relatively high rates of tick exposure, dogs may serve as sentinels of risk for RMSF in people [3], [15]–[17]. The drug of choice for treating RMSF in dogs, as in humans, is doxycycline with the recommended treatment regimens of either 5–10 mg/kg/day for 10–21 days [18], or 10–20 mg/kg twice/day for 1 week [19] regardless of the age of the dog. Either regimen is reported to lead to quick subsidence of a fever and complete recovery with no expected sequelae or relapses.
Although clinical signs of R. rickettsii infection in dogs have been described, the majority of published reports present descriptions of either advanced clinical cases [9], [12], [20]–[22], or experimental infections caused by needle-inoculation of cultured pathogen rather than by tick bite [23]–[26]. The natural progression of a R. rickettsii infection in a canine model following exposure to infected D. variabilis has not been studied in sufficient detail, especially prior to the onset of evident clinical signs.
Here, we describe the progression of clinical disease via hematological, molecular, and serological data in dogs...