diphyllobothrium nihonkaiense is a parasite prevalent in korea and japan , but rare in china , russia , north america , oceania , and europe [ 1 - 7 ] . d. nihonkaiense has been inaccurately diagnosed as d. latum ; however , this erroneous identification can be revised using dna sequencing . although the treatment is the same for both species , the disease severity and treatment results may vary only with limited evidence . many case reports have indicated salmon intake as the source of d. latum infection in korea ; however , salmon intake is now more indicative of d. nihonkaiense infection . other sea fish species from the pacific ocean   may also act as intermediate hosts for d. nihonkaiense . dna analysis of suspected d. latum samples collected and examined in korea indicated the presence of d. nihonkaiense . we performed dna analysis of 4 diphyllobothrium samples from patients referred to the parasitology department of hallym university , korea between 1995 and 2014 and identified them as d. nihonkaiense . proglottids of diphyllobothrium were obtained from 4 patients referred to the parasitology department of hallym university , chuncheon , korea from november 1995 to february 2014 and stored in 100% ethanol . only 1 patient in 2014 the patient resided in inje - gun , gangwon - do , and frequently visited sokcho - si , gangwon - do to consume raw fish ( = sashimi ) . the patient consumed raised halibut , raised rockfish , blowfish , flounder , filefish , raised mullet , sea squirt , whelk , and squid , but had no salmon intake history . the patient s wife also consumed sashimi but not mullet because of personal preference . in november 2012 , the patient experienced repeated bouts of loose stools . the patient observed a 2-m long parasite while defecating and tried to remove it , but it ruptured . it is notable that normal stools transformed into loose stools at the point of release of the parasite . the patient received treatment with albendazole ( 400 mg ) , after which the same parasite ( a part ) was excreted . he was treated with albendazole ( 400 mg ) for 3 more days but the medication had no effects . the patient continued medication for 4 more days , with repeated excretion of the parasite . the parasite excretion lasted 1 month when only 1 parasite was observed , and the excretion started to decrease thereafter . however , in february 2014 , 2 - 3 segments of parasites were observed during defecation . each parasite segment was 3 - 4 m long , and ruptured when the patient attempted to manually remove them . the doctor referred the patient to the parasitology department of hallym university for identification of the parasite , and prescribed praziquantel ( 10 mg / kg in a single dose ) . the day after initiation of the therapy , a single dead parasite live parasites expelled previously moved actively and were white to mild yellowish in color , whereas the dead parasite was darker yellowish in color . the proglottid but not the scolex was observed in the parasite . the patient was monitored for 3 months , with no symptoms of infection recurrence , including loose stool . of the 4 diphyllobothrium samples collected from patients , 3 were stored at the parasitology department , hallym university college of medicine in chuncheon , gangwon - do , and 1 at the parasitology department at inje - gun , gangwon - do . the 4 samples were sent to the department of parasitology , chungbuk national university school of medicine for dna analysis . a single proglottid was cut into small pieces , and total genomic dna was extracted using a dneasy tissue kit ( qiagen , valencia , california , usa ) according to manufacturer s instructions . pcr was performed in a reaction mixture containing 50 l with 0.01 g/l of genomic dna , 10 pcr buffer ( 20 mm mg ) , 10 mm dntp mixture , 10 pmoles of each primer , and 2.5 u/l taq dna polymerase ( high fidelity pcr system , roche , mannheim , germany ) using a geneamp pcr system 9700 ( applied biosystems , langen , germany ) . the primers used were d1f ( 5-tgtgtgggggcatcatatgt-3  ) and d1r ( 5-atgataaggaacaggagctcagcata-3  ) . the second pcr and sequencing primers used were d1f1 ( 5-gtttagatgtaaagacggctg-3  ) and d1r1 ( 5-ggtaaaccgcacacaccaaa-3  ) and yielded a 203-bp product corresponding to the position 919 - 1,122 bp of the cox1 gene ( fig . dna sequencing was performed using a big - dye terminator sequencing kit ( version 3.2 , applied biosystems , foster city , california , usa ) and the reaction products were separated on electrophoresis using an automated dna sequencer model 3739kl ( applied biosystems ) . dna sequences were assembled and aligned using geneious 7.0.2 software ( biometer , auckland , new zealand ) . phylogenetic analyses were performed using the neighbor - joining ( nj ) method and the mega software ( version 6 ) . nj analysis was performed using a distance matrix calculated with the kimura 2 parameter method . the sequences were identified using blast searches and compared with sequences of d. nihonkaiense and d. latum deposited in the genbank database . the cox1 sequences ( 203 bp ) of specimens 1 , 2 , 3 , and 4 showed 99.5% ( 202/203 ) , 98.5% ( 200/203 ) , 98.5% , and 99.5% similarities to a reference d. nihonkaiense sequence ( nc 008945 ) and 91.6% ( 186/203 ) similarity to a reference d. latum sequence ( nc 008945 ) , respectively ( fig . d. nihonkaiense was recognized as a new species for the first time by yamane et al . in 1986 . d. latum has been primarily identified because of its morphological resemblance with d. nihonkaiense , but after 2009 , d. nihonkaiense was confirmed by dna analysis in all cases . our additional 4 cases support the evidence that most or all of the diphyllobothriid tapeworms in korea are d. nihonkaiense but not d. latum . in addition , there was no dna evidence of d. latum infection in korea . in particular , patients with a salmon intake history are unlikely to be infected with d. latum . therefore , during an initial morphological diagnosis of diphyllobothrium infection , d. nihonkaiense infection should be suspected first . a single dose of praziquantel ( 10 mg / kg ) has been recommended for the treatment of d. nihonkaiense infection , similar to the dose used to treat d. latum infection . however , in 1 case of suspected d. nihonkaiense infection , a single dose of praziquantel caused a continuous stomachache , which required an additional dose for recovery . moreover , the medical history of 3 patients could not be obtained and evaluated . in conclusion , these 4 cases support the evidence of d. nihonkaiense infection in korea . further dna sequencing studies are required for accumulation of evidence to prevent misidentification of d. latum in korea .
most of the diphyllobothriid tapeworms isolated from human samples in the republic of korea (= korea ) have been identified as diphyllobothrium nihonkaiense by genetic analysis . 
 this paper reports confirmation of d. nihonkaiense infections in 4 additional human samples obtained between 1995 and 2014 , which were analyzed at the department of parasitology , hallym university college of medicine , korea . 
 analysis of the mitochondrial cytochrome c oxidase 1 ( cox1 ) gene revealed a 98.5 - 99.5% similarity with a reference d. nihonkaiense sequence in genbank . 
 the present report adds 4 cases of d. nihonkaiense infections to the literature , indicating that the dominant diphyllobothriid tapeworm species in korea is d. nihonkaiense but not d. latum .