Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 5 1 2011 06 15 7 12 EN SR Naddaf Department of Parasitology, Pasteur Institute of Iran, Tehran, Iran M Kishdehi Department of Microbiology, Lahijan Azad University, Gilan, Iran MR Siavashi Department of Parasitology, Pasteur Institute of Iran, Tehran, Iran 2015 10 03    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 flaB, 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 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 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.   https://jad.tums.ac.ir/index.php/jad/article/view/78 https://jad.tums.ac.ir/index.php/jad/article/download/78/76