Abstract: The 18S rRNA gene recently discovered was shown to be species-specific. A pair of primers was designed to specifically amplified a 452 bp fragment. The PCR result of specificity assay showed that one references B.caballi could be detected by the PCR test,but no amplification was observed when other five bacterial species isolated from T.equi,B.bigimina,B.motasi,B.ovata,B.major tissue were detected. And the sensitivity result showed that the minimum dose of B.caballi that could be detected by PCR assay was 0.01 fg/μL,45 clinical sample,from horses farm in China,doubtedly infected with B.caballi were tested by PCR. The results showed that 12 positive samples could be detected by the PCR assay. At the same time,microscope were also used for the clinical samples. The test revealed that the sensitivity of the PCR assay was higher than that the microscope test.

Key words: Babesia caballi; PCR diagnosis method; application