Dibothriocephalus nihonkaiensis infection identified by pathological and genetic analyses -a case report and a recent literature review of human diphyllobothriasis

Abstract

We report a 20-year-old male with a past history of diarrhea and discharge of a strobila of a broad tapeworm from his anus 3 months ago. He again noticed passing a tapeworm strobila and he visited our hospital with the tapeworm sample. The macroscopic appearance and the pathological features strongly suggested Diphyllobothriasis. Soon after the first visit to our hospital, a capsule endoscopy was performed with the result of no evidence of strobilae or scoleces. Praziquantel at 20 mg/kg was orally administered once. Before drug administration, egg-like structures were present in the stool. They disappeared soon after drug administration. In human Diphyllobothriasis, Dibothriocephalus nihonkaiensis (D. nihonkaiensis) infection and Dibothriocephalus latus (D. latus) infection are common. These two species are morphologically similar but genetically distinct. Accordingly, polymerase chain reaction (PCR) using genomic DNA of the tapeworm infecting our case was performed for amplifying mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. The amplified DNA fragment by PCR of our case was phylogenetically compared with other mitochondrial cox1 gene sequences of D. nihonkaiensis, D. latus, D. dendriticus, Taenia saginata, Taenia solium and Spirometra erinaceieuropaei. As a result, the tapeworm of our case was most likely within the spectrum of D. nihonkaiensis. Although human diphyllobothriasis is not a life-threatening disease for human beings, it has become a re-emerging problem even in the most developed countries with the increasing popularity of eating raw fish. The knowledge of how to cook or freeze raw fish before eating can reduce the risk of infection. However, without general awareness of human parasite infection, food-borne infections will continue to be a public health problem. Keywords: Tapeworm, Dibothriocephalus nihonkaiensis, Dibothriocephalus latus, Mitochondrial cytochrome c oxidase subunit 1 gene, Praziquantel