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 mi-cros-copy. This study is aimed to evaluate the sensitivity of different methods developed for detection of low-grade spi-ro-chetemia. Methods: Animal blood samples with low degrees of spirochetemia were tested with two PCRs and a nested PCR tar-get-ing flaB, GlpQ, and rrs genes. Also, a centrifuged-based enrichment method and Giemsa staining were per-formed on blood samples with various degrees of spirochetemia. Results: The flaB-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 spi-ro-chete 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 concentra-tion 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.