Early detection and estimation of infection burden by real-time PCR in rats experimentally infected with Clonorchis sinensis

A real-time PCR assay targeting the cytochrome c oxidase gene of Clonorchis sinensis was developed and its diagnostic value was investigated in experimentally infected rats. The PCR assay amplified as little as 0.1 pg of C. sinensis genomic DNA and a single egg from experimentally spiked negative feces. The assay could detect C. sinensis DNA in feces 2 weeks post-infection (PI), whereas the Kato-Katz method and formalin-ether concentration techniques could detect the eggs in the feces from 3 weeks PI. Inverse correlations between eggs per gram of feces (EPG) and Ct values were observed 4, 6, and 8 weeks PI. Worm burden was positively correlated with EPG but negatively correlated with Ct values in different groups at 8 weeks PI. Fecal real-time PCR provides a potential tool for the diagnosis of clonorchiosis before eggs can be detected by conventional methods, and may be used to estimate the worm burden in the host.