Characterization of Fasciola samples from different host species and geographical localities in Spain by sequences of internal transcribed spacers of rDNA

In the present study, 25 samples representing Fasciola (Platyhelminthes: Trematoda: Digenea) from nine host species and 19 geographical locations in Spain were characterized genetically by sequences of the first (ITS-1) and second (ITS-2) internal transcribed spacers (ITS) of nuclear ribosomal DNA (rDNA). The ITS rDNA was amplified from individual liver flukes by polymerase chain reaction (PCR), and the amplicons were sequenced directly. The lengths of the ITS-1 and ITS-2 sequences were 422 and 362 bp, respectively, for all Spanish liver fluke samples sequenced. Comparison of the ITS sequences of the Spanish Fasciola samples examined in the present study with that of Fasciola hepatica, Fasciola gigantica and the "intermediate Fasciola" revealed that all Spanish Fasciola samples examined represent the single species of F. hepatica, with only slight sequence variation in the ITS-2 (1/362, 0.3%) among the sequenced samples, but the sequence variation was not related to particular host species and/or geographical origins of the samples. The Spanish F. hepatica examined differed from Fasciola from elsewhere by two nucleotides in the ITS-2, which provided genetic marker for the differentiation of Spanish F. hepatica from Fasciola from other geographical localities. These results have implications for studying the population genetic structure of the Spanish F. hepatica and for the diagnosis and control of the disease it causes.