Two-step PCR in the evaluation of antibiotic treatment for Ehrlichia platys infection.

We evaluated the feasibility of using the two-step polymerase chain reaction (PCR) in determining the withdrawal time of antibiotic treatment for Ehrlichia platys infection. We also present experimental evidence of a dog remaining a carrier after treatment with tetracycline. Canine infectious cyclic thrombocytopenia (CICT) was induced in 3 dogs by intravenous inoculation of blood infected with E. platys. Tetracycline was administered to one of the dogs for 2 weeks when parasitemia appeared. Although the hematologic abnormality of cyclic thrombocytopenia soon disappeared, a few parasitized platelets reappeared after the withdrawal of treatment, and the dog thus remained as a carrier. The other dogs were treated with doxycycline when parasitemic episodes first developed. The durations of antibiotic regimens were determined by the results of two-step PCR in which the 16S rDNA of E. platys was amplified from blood samples. Doxycycline was withdrawn after 8 days of treatment, and the follow-up monitoring continued for 3 weeks. The platelet counts of the 2 dogs remained within the normal range, and the etiologic agent of CICT was not found either by Giemsa staining or by the two-step PCR, indicating complete elimination of the agent.