CHARACTERIZATION OF A NEW ISOLATE OF EHRLICHIA-PLATYS (ORDER RICKETTSIALES) USING ELECTRON-MICROSCOPY AND POLYMERASE CHAIN-REACTION

A mixed-breed pup approximately 3 months old obtained in north central Oklahoma by the Laboratory Animal Resources Unit of Oklahoma State Un iversity presented with platelet inclusions. The dog developed severe thrombocytopenia (< 10 000 mu l(-1)) following the appearance of inclu sions. Blood films were monitored daily and when about 75% of platelet s had inclusions, samples were collected in EDTA and processed for ele ctron microscopic (EM) studies and polymerase chain reaction (PCR). EM studies on glutaraldehyde-fixed buffy coat revealed rickettsia-like i nclusions in numerous platelets. Serologic examination, using Ehrlichi a platys antigen, showed high titre suggestive of E. platys infection. PCR primers derived from a highly variable region of the 16S rRNA gen e sequence of E. platys were used to specifically amplify that region of the parasite's DNA. Sequencing of the PCR product obtained by gener al Ehrlichia primers showed one nucleotide difference from the publish ed sequence for E. platys which suggests possible strain variation of this intracellular parasite. Our results indicate that PCR may be a us eful tool in the diagnosis of E. platys infection and that, like other Ehrlichia spp., E. platys isolates may vary.