Application of the polymerase chain reaction for the detection of Ehrlichia canis in tissues of dogs

Doxycycline treatment resulted in a carrier status in 3 dogs and complete clearance of Ehrlichia canis in 2 dogs (Iqbal and Rikihisa, 1994). Using specimens obtained during that study applicability of polymerase chain reactions (PCRs) in detecting E. canis DNA in tissue specimens and correlation of PCR results with our previous cell culture isolation results were evaluated. PCRs using a pair of primers specific to E. canis 16SrRNA gene sequence were used to detect DNA of E. canis in tissues of 5 experimentally-infected dogs 2 months after doxycycline treatment. An approximately 600 bp product defined by the specific primers was amplified in blood, kidney, lymph nodes, liver, and/or spleen of 3 dogs from which E. canis was reisolated in cell culture. In contrast, E. canis DNA was not detected in tissue or blood specimens of the 2 dogs from which E. canis was not reisolated after doxycycline treatment or in 2 control uninfected dogs. The findings indicate PCR is effective in detecting E. canis in tissues.