Global analysis of cytochrome c oxidase subunit 1 (cox1) gene variation in Dibothriocephalus nihonkaiensis (Cestoda: Diphyllobothriidae).

The cestode Dibothriocephalus nihonkaiensis (syns. Diphyllobothrium nihonkaiense and Diphyllobothrium klebanovskii), the broad fish tapeworm, is a parasitic agent of intestinal infection acquired by consumption of raw or undercooked Pacific salmon, Onchorhynchus spp. Sequencing studies conducted about a decade ago revealed the presence of two major lineages (A and B) in the broad fish tapeworm population within Asian coastal areas. However, in spite of the accumulation of sequence data on GenBank recently, no further genetic analyses of D. nihonkaiensis have been attempted. The present study assessed for the first time the global cox1 variation in D. nihonkaiensis. Novel partial cox1 sequences of 14 isolates of D. nihonkaiensis from 12 patients were generated, and a global genetic analysis was performed using the 14 novel and 79 previously published sequences for isolates from definitive and second intermediate hosts of this species was performed. A total of 48 haplotypes of three haplotype groups (Types A, B and C) were identified, and co-infections with genetically different D. nihonkaiensis were highlighted in humans and Pacific salmon.