Predominance ofEhrlichia ewingiiin Missouri Dogs

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Abstract
To investigate the species distribution ofEhrlichiapresent in Missouri dogs, we tested 78 dogs suspected of having acute ehrlichiosis and 10 healthy dogs. Blood from each dog was screened with a broad-range 16S rRNA gene PCR assay that detects known pathogenic species ofEhrlichiaandAnaplasma. The species was determined by using species-specific PCR assays and nucleotide sequencing.Ehrlichiaantibody testing was performed by using an indirect immunofluorescence assay withEhrlichia chaffeensisas the antigenic substrate. The broad-range assay detectedEhrlichiaorAnaplasmaDNA in 20 (26%) of the symptomatic dogs and 2 (20%) of the asymptomatic dogs.E. ewingiiaccounted for 20 (91%), andE. chaffeensisaccounted for 1 (5%) of the positives.Anaplasma phagocytophilumDNA was detected in one dog, and the sequences of regions of the 16S rRNA gene and thegroESLoperon amplified from the blood of this dog matched the published sequences of this organism. Antibodies reactive withE. chaffeensiswere detected in 14 (67%) of the 21 PCR-positive dogs and in 12 (19%) of the 64 PCR-negative dogs. Combining the results of PCR and serology indicated that 33 (39%) of 85 evaluable dogs had evidence of past or currentEhrlichiainfection. We conclude thatE. ewingiiis the predominant etiologic agent of canine ehrlichiosis in the areas of Missouri included in this survey.E. canis, a widely recognized agent of canine ehrlichiosis, was not detected in any animal. The finding ofE. ewingiiin asymptomatic dogs suggests that dogs could be a reservoir for thisEhrlichiaspecies.

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