Comparison of PCR with other tests for early diagnosis of canine ehrlichiosis.

The purpose of the study was to compare the sensitivity of PCR with those of cell culture reisolation of Ehrlichia canis, the indirect fluorescent antibody test (IFA), and Western immunoblotting (WI) in the early diagnosis of canine ehrlichiosis. Five German shepherd dogs were intravenously inoculated with 10(7) E. canis-infected DH82 cells. Blood was collected on alternate days during a 2-week postinoculation period. Mononuclear cell fractions were harvested and used for E. canis reisolation and DNA extraction for PCR. The plasma was used for assaying antibodies against E. canis. By PCR, the 16S rRNA gene of E. canis was detected in the mononuclear cell specimens collected as early as day 4 to 10 postexposure (PE). E. canis was reisolated from the blood starting on day 2 PE from all five dogs. The indirect fluorescent antibody test and Western immunoblotting could detect E. canis antibodies as early as 2 to 8 days PE. Cell culture reisolation proved to be the most sensitive and definitive for early diagnosis of ehrlichiosis, but it is not very convenient, since it takes a long time (14 to 34 days) to show up positive. The sensitivity of PCR is comparable to or slightly less than that of other established methods; however, the convenience, quickness, and direct nature of detecting E. canis DNA is expected to make PCR more useful for clinical diagnosis.