Morphologic and Genetic Identification of Diphyllobothrium nihonkaiense in Korea

Abstract

Diphyllobothrium nihonkaiense was first described by Yamane in 1986 but the taxonomical features have been obscure due to lack of critical morphologic criteria in its larval and adult stages. In Korea, this tapeworm had long been known as Diphyllobothrium latum. In this study, we observed 62 specimens collected from Korean residents and analyzed them by morphological features and nucleotide sequences of mitochondrial cox1 gene as well as the ITS1 region. Adult tapeworms were examined after carmine or trichrome stain. Longitudinal sections of the gravid proglottids showed an obtuse angle of about 150 degree between the cirrus sac and seminal vesicle. This angle is known as a major differential point compared with that of D. latum. Nucleotide sequence differences between D. latum and the specimens from Koreans represented 17.3% in mitochondrial DNA cox1 gene. Sequence divergence of ITS1 among 4 Korean isolates was 0.3% and similarity was 99.7% with D. nihonkaiense and D. klebanovskii. All of the Korean specimens analyzed in this study were identified as being D. nihonkaiense (n = 62). We propose its Korean name as "Dong-hae-gin-chon-chung" which means 'long tapeworm of the East Sea' for this newly analyzed diphyllobothriid tapeworm in Korea.

Multiplex PCR for Differential Identification of Broad Tapeworms (Cestoda:Diphyllobothrium) Infecting Humans

“…Thanks to the use of molecular tools, locally acquired infections with allochtonous species are being reported more and more frequently. For instance, D. nihonkaiense, usually present in Japan and South Korea (8), has recently been detected in Switzerland (18,23), France (15,30), Finland (26), and North America (25). D. dendriticum, common in northern Europe, was found in a Swiss patient (24).…”

Diphyllobothrium nihonkaiense: wide egg size variation in 32 molecularly confirmed adult specimens from Korea

“…Molecular studies provided the diagnosis of D. nihonkaiense for all 32 specimens. Jeon et al (2009) previously reported the molecular diagnosis of 28 specimens, and that of the remaining four specimens is reported in the current study. The study followed the ethical guidelines of Seoul National University College of Medicine, Seoul, Korea.…”

“…Infection with the latter species is reportedly on the rise in Asia, including Japan (Arizono et al 2009a), China (Chen et al 2014), and South Korea (= Korea) (Jeon et al 2009;Park et al 2013;Song et al 2014;Kim et al 2014;Shin et al 2014). Sporadic infections with D. nihonkaiense were also detected in Europe (Yera et al 2006;Wicht et al 2007), America (Wicht et al 2008), and New Zealand (Yamasaki and Kuramochi 2009), possibly due to an increased global consumption of pacific salmon, the major source of D. nihonkaiense infection (Arizono et al 2009a).…”

“…However, diphyllobothriids show substantial variations in egg size, and a great size overlap exists between species, with resultant taxonomic limitation (Andersen and Halvorsen 1978). Despite the occurrence of only D. nihonkaiense in Korea (Jeon et al 2009), some Korean diphyllobothriasis cases revealed eggs larger ) than the reported values of D. nihonkaiense eggs, which highlights the need for precise differentiation between the two species and verification of their egg size range. Thus, in this study, we measured the length and width of eggs from 32 D. nihonkaiense (molecularly proven) adult specimens recovered from Korean patients to determine the egg size range of D. nihonkaiense.…”

“…However, D. nihonkaiense is under-recognized because of its close morphologic similarities with the classical D. latum. Recent genetic studies in Asia (Korea, Japan, and China) suggested that all previous cases diagnosed as D. latum were in fact D. nihonkaiense (Jeon et al 2009;Arizono et al 2009a;Chen et al 2014).…”