Four Human Cases of Diphyllobothrium nihonkaiense (Eucestoda: Diphyllobothriidae) in China with a Brief Review of Chinese Cases

Human diphyllobothriosis in Taiwan: A review of cases and molecular evidence of Dibothriocephalus nihonkaiensis

Diphyllobothriosis is an infectious disease caused by the consumption of raw freshwater or marine fish containing larvae of broad tapeworms (Diphyllobothriidae). In the present study, we critically reviewed all cases of human diphyllobothriosis reported from Taiwan, including unpublished reports from hospitals in Taipei. Genotyping based on mitochondrial DNA marker (cox1) confirmed that two of the recent cases were caused by Dibothriocephalus nihonkaiensis, which is not native to Taiwan and was probably imported with Pacific salmon infected with larvae of D. nihonkaiensis. The causative species previously reported in Taiwan could not be definitively confirmed. However, considering the distribution of Dibothriocephalus latus, which is not endemic in Taiwan, past cases diagnosed as D. latus are questionable.

Ups and downs of infections with the broad fish tapeworm Dibothriocephalus latus in Europe (Part II) and Asia from 1900 to 2020

The broad fish tapeworm, Dibothriocephalus latus (Diphyllobothriidea), is the most important causative agent of diphyllobothriosis, a fish-borne zoonosis, in Europe. Part I of this review focused on the occurrence of D. latus in northwestern and central Europe, particularly in Fennoscandia, the Baltic, the Alpine lakes and Danube River regions during 1900-2020. Part II summarises data on D. latus from the European and Asian parts of Russia and from Asian countries. The tapeworm has occurred throughout Russia, with the most important foci in (i) the Republic of Karelia in the northwest of European Russia, (ii) the Volga River basin in the central and southern parts of European Russia, (iii) the Ob-Irtysh rivers region in the Ural region, (iv) the Yenisei-Lena rivers region in Siberia, and (v) the Lake Baikal basin in Siberia. The incidence of diphyllobothriosis has declined in recent decades, especially in European Russia, but zoonosis is still prevalent in some regions of Siberia. Cases reported from Arctic regions, the region around Lake Baikal, and the Pacific coast, including the Amur basin, however, were probably misidentifications with D. dendriticus and/or D. nihonkaiensis. No other Asian country where D. latus findings represented either imported cases or misidentifications had natural focus of diphyllobothriosis. Patterns of distribution of D. latus occurrence were similar in all Eurasian foci between 1900 and 2020. The numbers of records were associated with historical and epidemiological milestones of particular time periods.

Global analysis of cytochrome c oxidase subunit 1 (cox1) gene variation in Dibothriocephalus nihonkaiensis (Cestoda: Diphyllobothriidae)

The cestode Dibothriocephalus nihonkaiensis (syns. Diphyllobothrium nihonkaiense and Diphyllobothrium klebanovskii), the broad fish tapeworm, is a parasitic agent of intestinal infection acquired by consumption of raw or undercooked Pacific salmon, Onchorhynchus spp. Sequencing studies conducted about a decade ago revealed the presence of two major lineages (A and B) in the broad fish tapeworm population within Asian coastal areas. However, in spite of the accumulation of sequence data on GenBank recently, no further genetic analyses of D. nihonkaiensis have been attempted. The present study assessed for the first time the global cox1 variation in D. nihonkaiensis. Novel partial cox1 sequences of 14 isolates of D. nihonkaiensis from 12 patients were generated, and a global genetic analysis was performed using the 14 novel and 79 previously published sequences for isolates from definitive and second intermediate hosts of this species was performed. A total of 48 haplotypes of three haplotype groups (Types A, B and C) were identified, and co-infections with genetically different D. nihonkaiensis were highlighted in humans and Pacific salmon.

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First global analysis of cox1 variation in Dibothriocephalus nihonkaiensis.

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First application of haplotype network analysis for a D. nihonkaiensis population.

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A total of 48 haplotypes of three haplotype groups (Type A, B and C) are identified.

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Co-infections with heterogenic isolates in definitive and intermediate hosts are highlighted.

Dibothriocephalus nihonkaiensis: an emerging foodborne parasite in Brittany (France)?

BACKGROUND

Diphyllobothriosis is an intestinal cestodosis caused by tapeworms of the family Diphyllobothriidae. In France, endemic cases are limited to south-east and due to Dibothriocephalus latus. In this paper, we investigate a series of seven cases of diphyllobothriosis in the non-endemic French region of Brittany. All have been diagnosed between 2016 and 2018 at the University Hospital of Rennes.

METHODS

Parasites were identified by their morphological features and by phylogenetic analysis of the cox1 gene. Phylogenetic tree was built using maximum likelihood criterion under the GTR+G+I model and 2000 bootstrap replicates. A form was sent to all patients to collect data concerning clinical signs and possible sources of infection.

RESULTS

All cases were due to Dibothriocephalus nihonkaiensis, a species strictly distributed in the North Pacific. Epidemiological investigation showed that the parasite was probably acquired in France, after consumption of Japanese food containing raw salmon. All patients presented with at least abdominal pain and fatigue except for one patient who had no symptoms.

CONCLUSIONS

To our knowledge, this case series is the most important cohort of allochthonous diphyllobothriosis described in Europe. This sudden emergence raises concern about foodborne infections, highlighting (i) risky food habits in absence of adequate sanitary control; and (ii) the breaking of the rule of geographical restriction due to globalization and worldwide trades.

Epidemiology of Diphyllobothrium nihonkaiense Diphyllobothriasis, Japan, 2001-2016

The threat from this disease, the most common cestodiasis in Japan, is increasing because of globalization and lack of awareness.

We report 958 cases of cestodiasis occurring in Japan during 2001–2016. The predominant pathogen was Diphyllobothrium nihonkaiense tapeworm (n = 825), which caused 86.1% of all cases. The other cestode species involved were Taenia spp. (10.3%), Diplogonoporus balaenopterae (3.3%), and Spirometra spp. (0.2%). We estimated D. nihonkaiense diphyllobothriasis incidence as 52 cases/year. We observed a predominance of cases during March–July, coinciding with the cherry salmon and immature chum salmon fishing season, but cases were present year-round, suggesting that other fish could be involved in transmission to humans. Because of increased salmon trade, increased tourism in Japan, and lack of awareness of the risks associated with eating raw fish, cases of D. nihonkaiense diphyllobothriasis are expected to rise. Therefore, information regarding these concerning parasitic infections and warnings of the potential risks associated with these infections must be disseminated to consumers, food producers, restaurant owners, physicians, and travelers.