Update on the Human Broad Tapeworm (GenusDiphyllobothrium), Including Clinical Relevance

Abstract

SUMMARYTapeworms (Cestoda) continue to be an important cause of morbidity in humans worldwide. Diphyllobothriosis, a human disease caused by tapeworms of the genusDiphyllobothrium, is the most important fish-borne zoonosis caused by a cestode parasite. Up to 20 million humans are estimated to be infected worldwide. Besides humans, definitive hosts ofDiphyllobothriuminclude piscivorous birds and mammals, which represent a significant zoonotic reservoir. The second intermediate hosts include both freshwater and marine fish, especially anadromous species such as salmonids. The zoonosis occurs most commonly in countries where the consumption of raw or marinated fish is a frequent practice. Due to the increasing popularity of dishes utilizing uncooked fish, numerous cases of human infections have appeared recently, even in the most developed countries. As many as 14 valid species ofDiphyllobothriumcan cause human diphyllobothriosis, withD. latumandD. nihonkaiensebeing the most important pathogens. In this paper, all taxa from humans reported are reviewed, with brief information on their life history and their current distribution. Data on diagnostics, epidemiology, clinical relevance, and control of the disease are also summarized. The importance of reliable identification of human-infecting species with molecular tools (sequences of mitochondrial genes) as well as the necessity of epidemiological studies aimed at determining the sources of infections are pointed out.

Seasonal and biogeographical patterns of gastrointestinal parasites in large carnivores: wolves in a coastal archipelago

“…This reflects coastal wolves' dietary shift of up to 70% Pacific salmon in the fall. Sequences from Diphyllobothrium eggs matched D. nihonkaiense, a species that infects salmonids (O. gorbuscha and O. keta) commonly available to coastal wolves (Scholz et al 2009). Notably, we found no evidence of the trematode Nanophyetus salmincola that carries the causative agent of salmon poisoning disease in canids, Neorickettsia helminthoeca (Foreyt, 2001a).…”

Diphyllobothrium pacificum Infection is Seldom Associated with Megaloblastic Anemia

“…One of its more conspicuous clinical manifestations in humans is megaloblastic anemia, which is caused by the parasite intake of vitamin B12 or folic acid within the host. [1][2][3][4] Clinically evident megaloblastic anemia is found in 2-3% of persons harboring a D. latum tapeworm, and 50% of D. latum carriers have low levels of serum vitamin B12 levels ( 100 pg/mL compared with 350-450 pg/mL in noninfected persons). 13 In Pacific coast regions of South America, diphyllobothriasis is usually caused by D. pacificum, which is a shorter tapeworm (approximately 1 meter in length), but can have a length of 4 meters on rare occasions.…”

“…13 In these cases, oral or parenteral vitamin B12 administration after parasite expulsion brings levels back to reference range. 13 Diphyllobothrium pacificum infection (Nybellin 1931, Margolis 1956 15 is endemic to the Pacific coasts of South America and southern Asia, 1,6 and is the only type of diphyllobothriasis described in Peru to date. It was present before the European colonization, as demonstrated by the finding of characteristic eggs in pre-Hispanic mummies.…”

“…1,2,[10][11][12][13] In Nordic countries, megaloblastic anemia secondary to dyphillobothriasis has been reported. 13 In these cases, oral or parenteral vitamin B12 administration after parasite expulsion brings levels back to reference range.…”

“…[1][2][3] Humans are an accidental definitive host of these parasites, which usually infect sea lions or fur seals, 1 and usually harbor a single tapeworm, which in the case of D. latum, may reach 12 meters in length. 1,4 Diphyllobothrium eggs are ovoid, operculated, and nonembryonated, and have a maximal diameter of 50-60 μm. A ciliated embryo is released in an aquatic environment and infects microcrustaceans, which serve as intermediate invertebrate hosts for the parasite.…”