Genetic characterization of Fasciola gigantica from different geographical regions of India by ribosomal DNA markers.

Ribosomal DNA sequences of the second internal transcribed spacer (ITS-2) and 28S ribosomal DNA (618 bp) of Fasciola gigantica collected from cattle and buffaloes from four different geographical locations of India, were characterized for genotyping. ITS-2 sequence was analyzed in 28 worms that was typical of F. gigantica and differed at six positions, with one of these being a distinguishing deletion (T) at the 327th position in F. gigantica relative to F. hepatica. However, Fasciola specimens also showed intraspecies sequence polymorphism in the ITS-2, with two different ITS-2 sequences existing in the ribosomal DNA (rDNA) array within a single Fasciola worm. One of the sequences was identical to that of F. gigantica and the other showed extensive sequence polymorphism in the ITS-2. Using BspH1-restriction fragment length polymorphism, six variable ITS-2 sequences in F. gigantica were identified within these parasite specimens and were found distributed in these four geographical regions. 28S rDNA sequence of 24 flukes, collected from the above four geographical regions, showed a single nucleotide polymorphism at 284th nucleotide (G/A). Analyzing the sequence data of 28S rDNA of F. gigantica available from some African and Asian countries for this polymorphic 284th nucleotide position, it is proposed that there are two basic lineages of the F. gigantica for 28S rDNA existing in the fluke populations from five African and several Asian countries.