The University of Georgia College of Veterinary Medicine

Georgia Veterinary Scholars Program

GVSP Summer 2006 Scholars

Georgia Veterinary Scholar	Faculty Mentor

Sean Adams University of Georgia Class of 2008	Dr. Michael Yabsley

Experimental infection of domestic dogs with Ehrlichia ewingii

Dustin S. Adams1*, Michael J. Yabsley1,2, and Thomas P. O’Connor3

1 Southeastern Cooperative Wildlife Disease Study, College of Veterinary Medicine, University of Georgia, Athens, Ga.; 2 Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Ga.; and 3 IDEXX Laboratories, Westbrook, Maine.

Ehrlichia ewingii causes granulocytotropic ehrlichiosis in dogs and humans and is proposed to persist in nature in a cycle involving white-tailed deer and the lone star tick (Amblyomma americanum). Little is known about the pathogenesis of E. ewingii in domestic dogs, but thrombocytopenia, fever, and lameness have been reported in naturally-infected dogs. The primary objective of this project was to investigate the course of E. ewingii infection in experimentally infected dogs by using a combination of physical examination, hematologic and biochemical analyses, and molecular (PCR) and serologic assays (IDEXX Laboratories). Because E. ewingii has not been successfully cultivated, experimental trials must be conducted using white blood cells (WBC) isolated from the blood of experimentally infected “donor dogs”. The infected donor dogs were maintained by IV serial passage using aliquots of frozen blood every 3-4 months and infection was determined by PCR and ELISA testing. The three donor dogs (135, 913, and 8) became PCR positive and seropositive for E. ewingii on DPI 17, 21, and 18 and 41, 17, and 21, respectively. For the experimental infection trials, WBC were isolated from 40 ml of blood collected from donor dog 8 and equal amounts were inoculated IV into two principal dogs (dogs 2 and 9), and the previously inoculated donor dogs 135 and 913. The donor dogs 135 and 913 were, at the time, 10 and 8 months post infection, respectively, and were PCR negative, but remained seropositive. A negative control dog was inoculated with WBC from a negative dog. All four inoculated dogs became PCR positive for E. ewingii on DPI 4 and dogs 2 and 9 became seropositive on DPI 11. Some infected dogs had intermittent fever, thrombocytopenia, and leukopenia. The trial will continue until DPI 60. Future work will include experimental infection trials of white-tailed deer fawns and tick-transmission trials from infected dogs to naïve deer and from infected deer to naïve dogs. These data will provide a better understanding of the infection dynamics of E. ewingii in domestic dogs and deer.