Molecular detection of Diphyllobothrium nihonkaiense in humans, China

Abstract

The cause of diphyllobothriosis in 5 persons in Harbin and Shanghai, China, during 2008-2011, initially attributed to the tapeworm Diphyllobothrium latum, was confirmed as D. nihonkaiense by using molecular analysis of expelled proglottids. The use of morphologic characteristics alone to identify this organism was inadequate and led to misidentification of the species.

Keywords: China; cestodiasis; diphyllobothriosis; diphyllobothrium; diphyllobothrium infection; latum; nihonkaiense; parasite; plerocoercoid; proglottid; strobila; tapeworm.

Figure 1

Diphyllobothriid samples examined in the present study, China, 2008–2012. A) Proglottids stained with acetic acid–carmine from case-patient 12. B–E) Sagittal sections of proglottids stained with hematoxylin-eosin from case-patients 16–19. cs, cirrus sac; ut, uterus; sv, seminal vesicle; ov, ovary; ga, genital atrium. Scale bar in panel A represents 2 mm; scale bars in panels B–E represent 500 μm.

Figure 2

Phylogenetic tree constructed by using the maximum likelihood algorithm (Kimura’s 2-parameter model) on the basis of the complete cox1 sequences of isolates from Diphyllobothrium species found in persons in China and related Diphyllobothrium species. Numbers at nodes are bootstrap values (1,000 replicates) and posterior probabilities (10⁶ generations) for maximum likelihood and Bayesian inference, respectively. Spirometra erinaceieuropaei was used as an outgroup. Scale bar indicates the number of base substitutions per site.