Inter- and intra-specific characterization of tapeworms of the genus Diphyllobothrium (Cestoda: Diphyllobothriidea) from Switzerland, using nuclear and mitochondrial DNA targets

Human diphyllobothriosis is caused by at least 14 species of cestodes belonging to the genus Diphyllobothrium. Molecular analysis by sequencing of nuclear and mitochondrial targets identifies some species at inter- and intra-specific level, and helps to reconstruct their phylogenetic relationships. Nevertheless, the suitability of further molecular targets deserves to be widened, and the comparison of samples of different geographical origin could allow their intra-specific characterization, which could also be useful for epidemiological purposes. In this study, we investigated inter- and intra-specific variability among tapeworms of the genus Diphyllobothrium, with focus on Diphyllobothrium latum, originated from Switzerland. Samples were analyzed by comparing the sequences of two nuclear and two mitochondrial DNA targets. We analyzed 27 samples belonging to 4 species (D. latum, Diphyllobothrium nihonkaiense, Diphyllobothrium dendriticum and Diphyllobothrium ditremum), 15 of which isolated from clinical cases (adults and eggs), 2 from wild canines, and 2 from fish of Swiss lakes (plerocercoid larvae); 8 samples of homologous species from other geographic origins were also sequenced and compared with the Swiss ones. Sequences of partial small subunit ribosomal RNA (18S rRNA) gene and partial internal transcribed spacers 1 and 2 (ITS1-2) were not useful even in inter-specific identification, whereas sequences of complete cytochrome c oxidase subunit 1 (cox1) and cytochrome b (cob) genes allowed us to assess inter- and intra-specific variations among the samples. Cox1 and cob could differentiate 3 and 5 haplotypes within the species D. latum. The results are discussed in the light of the anamneses provided by part of the patients.