A 7-year-old, neutered Labrador Retriever was presented to their veterinarian for acute onset of lethargy, inappetence, and epistaxis. On physical examination, the dog had a mild fever (102.8˚F) and dried blood around the nose. Blood was submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for CBC and chemistry panels. The chemistry panel was unremarkable. On the CBC, there was a marked thrombocytopenia (20,000 K/µL), mild lymphocytosis, and minimal decrease in HCT. Blood smear examination confirmed the thrombocytopenia. On the feathered edge of the blood smear, rare monocytes containing morula (Figure 1) were observed. Based on this finding, TVMDL’s Tick-Borne Pathogen Multiplex (rtPCR) test was performed and confirmed the presence of Ehrlichia canis.
Ehrlichiosis in dogs is most commonly caused by infections with Ehrlichia canis and Ehrlichia ewingii. In the acute phases of the disease, morulae can be observed within WBCs during blood smear examination. Morulae are cytoplasmic vacuoles filled with bacteria. E. canis can be spread by the brown dog tick and the American dog tick. Clinical signs include lethargy, anorexia, fever, and bleeding. CBC findings can vary, but thrombocytopenia is the most common finding. The lack of visible morulae on a blood smear does not rule out ehrlichiosis. When ehrlichiosis is suspected, confirmatory testing should include serologic tests and antigen detection (e.g. PCR). Diagnostic sensitivity is improved when both testing methods are performed concurrently. The overall prognosis for dogs with ehrlichiosis is good if the infection is diagnosed and treated early.
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