Genetic characterization and phylogenetic analysis of echinostomes.

We conducted this study to identify species and determine the phylogenetic relationships using ribosomal DNA (rDNA) sequences [partial sequences of 28S rDNA and second internal transcribed spacer (IT52)] of echinostomes collected from free-grazing ducks in Phitsanulok Province, Thailand. Four adult echinostomes were morphologically identified as Echinostoma revolutum, 4 as Hypoderaeulm conoideurn and 2 unidentified. Sequences of other species/isolates of echinostomes retrieved from the GenBank database were employed to compare and construct the phylogenetic tree. Three major lineages were found, namely, genus Echinostoma, genus Echinoparyphiulm and genus Hypoderaeulm. One of the unidentified echinostome specimen was 99% identical to and clustered with genus Echinoparyphiurm, whereas the other was located in the "revolutum" roup, but was closely related to the geographical isolates from America rather than from Thailand. This study indicates that 28S rDNA and 1T52 regions are suitable molecular markers for genetic characterization and phylogenetic analysis of echinostomes.