comparison of pcr-based diagnosis with centrifuged-based enrichment method for detection of borrelia persica in animal blood samples

background: the mainstay of diagnosis of relapsing fever (rf) is demonstration of the spirochetes in giemsa-stained thick blood smears, but during non fever periods the bacteria are very scanty and rarely detected in blood smears by mi­cros­copy. this study is aimed to evaluate the sensitivity of different methods developed for detection of low-grade spi­ro­chetemia. methods: animal blood samples with low degrees of spirochetemia were tested with two pcrs and a nested pcr tar­get­ing fla b, glpq , and rrs genes. also, a centrifuged-based enrichment method and giemsa staining were per­formed on blood samples with various degrees of spirochetemia. results: the fla b-pcr and nested rrs -pcr turned positive with various degrees of spirochetemia including the blood samples that turned negative with dark-field microscopy. the glpq -pcr was positive as far as at least one spi­ro­chete was seen in 5-10 microscopic fields. the sensitivity of glpq -pcr increased when dna from buffy coat layer (bcl) was used as template. the centrifuged-based enrichment method turned positive with as low concentra­tion as 50 bacteria/ml blood, while giemsa thick staining detected bacteria with concentrations ≥ 25000 bacteria/ml. conclusion: centrifuged-based enrichment method appeared as much as 500-fold more sensitive than thick smears, which makes it even superior to some pcr assays. due to simplicity and minimal laboratory requirements, this method can be considered a valuable tool for diagnosis of rf in rural health centers.