The partial sequence of cytochrome c oxidase subunit I (COI)
of three metacercariae were amplified using COI-OV-Hap (F) and
(R) primers under the PCR amplification conditions described by
Thaenkham et al. (2007). The PCR products were sequenced using
an ABI PRISM 3100 genetic analyzer. Partial COI sequences of 369
base-pair obtained from three metacercariae were aligned with
the COI sequences of O. viverrini Thai and Lao isolates downloaded
from the GenBank (accession no: EU022351 and EU022357) using
CLUSTAL W (Thompson et al., 1994), with the default setting. The
genetic distances were calculated under Kimura’s two-parameter
model with the MEGA 4.0 program (