Development of mitochondrial loop-mediated isothermal amplification for detection of the small liver fluke Opisthorchis viverrini (Opisthorchiidae; Trematoda; Platyhelminthes).

Mitochondrial DNA sequences offer major advantages over the more usual nuclear targets for loop-mediated isothermal amplification approaches (mito-LAMP) because multiple copies occur in every cell. Four LAMP primers [F3, FIP(F1c+F2), BIP(B1c+B2), and B3] were designed based on the mitochondrial nad1 sequence of Opisthorchis viverrini and used for a highly specific assay (mito-OvLAMP) to distinguish DNA of O. viverrini from that of another opisthorchiid (Clonorchis sinensis) and other trematodes (Haplorchis pumilio, Haplorchis taichui, Fasciola hepatica, and Fasciola gigantica). Conventional PCR was applied using F3/B3 primer pairs to verify the specificity of the primers for O. viverrini DNA templates. All LAMP-positive samples could be detected with the naked eye in sunlight, by gel electrophoresis (stained with ethidium bromide), and by addition of SYBR green I to the product in sunlight or under UV light. Only DNA from O. viverrini yielded amplification products by LAMP (and by PCR verification), and the LAMP limit of detection was as little as 100 fg (10(-4) ng DNA), indicating that this assay is 10 to 100 times more sensitive than PCR. Field testing was done using representative egg and metacercarial samples collected from localities where the fluke is endemic. With the advantages of simplicity, rapidity, sensitivity, and cost effectiveness, mito-OvLAMP is a good tool for molecular detection and epidemiology studies in regions or countries where O. viverrini is endemic, which can lead to more effective control of opisthorchiasis and trematodiasis.