NESTED POLYMERASE CHAIN-REACTION FOR DETECTION OF EHRLICHIA-RISTICII GENOMIC DNA IN INFECTED HORSES

A nested polymerase chain reaction was developed for amplifying a 529- bp segment of the 16S ribosomal RNA gene of Ehrlichia risticii from eq uine buffy coat cells. Confirmation of identity of the amplified bands was accomplished by Southern hybridization and DNA sequencing. The st udy indicated a detection limit of > 10 copies of the target gene, and specificity for E. risticii as based on a panel of test rickettsiae. Ticks (Ixodes pacificus) collected in an area of northern California e nzootic for equine monocytic ehrlichiosis were found to be negative fo r E. risticii DNA.