Molecular identification of Ehrlichia ewingii infection in dogs: 15 cases (1997-2001)

OBJECTIVE: To determine historical, physical examination, hematologic, and serologic findings in dogs with Ehrlichia ewingii infection. DESIGN: Retrospective study. ANIMALS: 15 dogs. PROCEDURE: In all dogs, infection with E ewingii was confirmed with a polymerase chain reaction (PCR) assay. Follow-up information and clarification of information recorded in the medical records was obtained by telephone interviews and facsimile correspondence with referring veterinarians and owners. RESULTS: Fever and lameness were the most common findings with each occurring in 8 dogs. Five dogs had neurologic abnormalities including ataxia, paresis, proprioceptive deficits, anisocoria, intention tremor, and head tilt. Neutrophilic polyarthritis was identified in 4 dogs. No clinical signs were reported in 3 dogs. The predominant hematologic abnormality was thrombocytopenia, which was identified in all 12 dogs for which a platelet count was available. Reactive lymphocytes were seen in 5 of 13 dogs. Concurrent infection with another rickettsial organism was identified in 4 dogs. Of the 13 dogs tested, 7 were seroreactive to E canis antigens. Morulae consistent with E ewingii infection were identified in neutrophils in 8 dogs. Treatment with doxycycline, with or without prednisone, resulted in a rapid, favorable clinical response in the 9 dogs for which follow-up information was available. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that PCR testing for E ewingii infection should be considered in dogs with fever, neutrophilic polyarthritis, unexplained ataxia or paresis, thrombocytopenia, or unexplained reactive lymphocytes, and in dogs with clinical signs suggestive of ehrlichiosis that are seronegative for E canis. Following treatment with doxycycline, the prognosis for recovery is good.