Taxonomic status of the Japanese triploid forms of Fasciola: comparison of mitochondrial ND1 and COI sequences with F. hepatica and F. gigantica.

Because it is difficult to identify morphologically the Japanese forms of Fasciola, additional taxonomic criteria are required. In order to clarify the genetic relationships between Fasciola hepatica, Fasciola gigantica, and the Japanese triploid forms of Fasciola, we compared nucleotide sequences of mitochondrial NADH dehydrogenase subunit 1 (ND1) and cytochrome c oxidase subunit I (COI) genes. Intraspecific variation in the ND1 and COI sequences was low, except for 1 specimen of F. gigantica in the ND1 sequence. The ND1 and COI sequences of Japanese triploid forms of Fasciola were nearly identical to those found in F. gigantica but were different from those of F. hepatica. Thus, the Japanese triploid forms of Fasciola are thought to be categorized as F. gigantica.