''Diphyllobothrium'' is a genus of tapeworms which can cause diphyllobothriasis in humans through consumption of

raw Raw is an adjective usually describing: * Raw materials, basic materials from which products are manufactured or made * Raw food, uncooked food Raw or RAW may also refer to: Computing and electronics * .RAW, a proprietary mass spectrometry dat ...

or undercooked fish. The principal species causing diphyllobothriasis is ''D. latum'', known as the broad or fish tapeworm, or broad fish tapeworm. ''D. latum'' is a

pseudophyllid Pseudophyllid cestodes (former order pseudophyllidea) are tapeworms with multiple "segments" (proglottids) and two bothria or "sucking grooves" as adults. Proglottids are identifiably pseudophyllid as the genital pore and uterine pore are locat ...

cestode Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of man ...

that infects fish and mammals. ''D. latum'' is native to Scandinavia, western Russia, and the Baltics, though it is now also present in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, especially the Pacific Northwest. In Far East Russia, ''D. klebanovskii'', having Pacific salmon as its second intermediate host, was identified. Other members of the genus ''Diphyllobothrium'' include '' D. dendriticum'' (the salmon tapeworm), which has a much larger range (the whole northern hemisphere), ''D. pacificum'', ''D. cordatum'', ''D. ursi'', ''D. lanceolatum'', ''D. dalliae'', and ''D. yonagoensis'', all of which infect humans only infrequently. In Japan, the most common species in human infection is ''D. nihonkaiense'', which was only identified as a separate species from ''D. latum'' in 1986. More recently, a molecular study found ''D. nihonkaiense'' and ''D. klebanovskii'' to be a single species.

Morphology

The adult worm is composed of three fairly distinct morphological segments: the scolex (head), the neck, and the lower body. Each side of the scolex has a slit-like groove, which is a bothrium for attachment to the intestine. The scolex attaches to the neck, or proliferative region. From the neck grow many proglottid segments which contain the reproductive organs of the worm. ''D. latum'' is the longest tapeworm in humans, averaging ten meters long. Unlike many other tapeworms, ''Diphyllobothrium'' eggs are typically unembryonated when passed in human feces. In adults, proglottids are wider than they are long (hence the name ''broad tapeworm''). As in all pseudophyllid cestodes, the

genital pores A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...

open midventrally.

Life cycle

Adult tapeworms may infect humans, canids, felines,

bear Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Nor ...

s, pinnipeds, and mustelids, though the accuracy of the records for some of the nonhuman species is disputed. Immature eggs are passed in feces of the mammal host (the definitive host, where the worms reproduce). After ingestion by a suitable freshwater crustacean such as a

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

(the first

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...

), the coracidia develop into procercoid larvae. Following ingestion of the copepod by a suitable second intermediate host, typically a minnow or other small freshwater fish, the procercoid larvae are released from the crustacean and migrate into the fish's flesh where they develop into a plerocercoid larvae (sparganum). The plerocercoid larvae are the infective stage for the definitive host (including humans). Because humans do not generally eat undercooked minnows and similar small freshwater fish, these do not represent an important source of infection. Nevertheless, these small second intermediate hosts can be eaten by larger predator species, for example trout, perch, walleye, and

pike Pike, Pikes or The Pike may refer to: Fish * Blue pike or blue walleye, an extinct color morph of the yellow walleye ''Sander vitreus'' * Ctenoluciidae, the "pike characins", some species of which are commonly known as pikes * ''Esox'', genus of ...

. In this case, the sparganum can migrate to the musculature of the larger predator fish and mammals can acquire the disease by eating these later intermediate infected host fish raw or undercooked. After ingestion of the infected fish, the plerocercoids develop into immature adults and then into mature adult tapeworms which will reside in the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

. The adults attach to the intestinal

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It is ...

by means of the two bilateral grooves ( bothria) of their scolices. The adults can reach more than 10 m (up to 30 ft) in length in some species such as ''D. latum,'' with more than 3,000 proglottids. One or several of the tape-like proglottid segments (hence the name tapeworm) regularly detach from the main body of the worm and release immature eggs in freshwater to start the cycle over again. Immature eggs are discharged from the proglottids (up to 1,000,000 eggs per day per worm) and are passed in the feces. The incubation period in humans, after which eggs begin to appear in the feces is typically 4–6 weeks, but can vary from as short as 2 weeks to as long as 2 years.http://web.gideononline.com/web/epidemiology/

Disease

Diphyllobothriasis is considered a parasitic, zoonotic infection. ''D. latum'' causes a wide spectrum of disease and severity. The tapeworm induces changes in the concentration of several immunomodulators in the host. It can also cause structural changes in the GI tract as it modulates neuroendocrine responses and enhances secretion and gut motility. Damage may also come from the body's immune response against the worm and its millions of eggs (around 1 million/day) mediated by mast cells, eosinophilic cell degranulations resulting to inflammatory cytokines. Diphyllobothriosis is considered as the most important fish-borne zoonosis with up to 20 million individuals infected. ''D. latum'' causes B12 deficiency in humans leading to megaloblastic or

pernicious ''Pernicious'' is a Thai-American supernatural horror film directed by James Cullen Bressack, who also wrote the story along with co-writer Taryn Hillin. The film stars Ciara Hanna, Emily O'Brien, and Jackie Moore. Cast * Ciara Hanna as Al ...

anemia. The worm absorbs around 80% of dietary B12 and prolonged infection can also cause abdominal pain, mechanical obstruction, and symptoms of iron deficiency anemia. Patients with prolonged infection of D. latum must also undergo B12 supplementations along with anti-parasitics such as

niclosamide Niclosamide, sold under the brand name Niclocide among others, is an anthelmintic medication used to treat tapeworm infestations, including diphyllobothriasis, hymenolepiasis, and taeniasis. It is not effective against other worms such as flukes ...

or praziquantel.Vuylsteke P, Bertrand C, Verhoef GE, Vandenberghe P. Case of megaloblastic anemia caused by intestinal taeniasis. Ann Hematol. 2004 Jul;83(7):487-8. doi: 10.1007/s00277-003-0839-2. Epub 2004 Jan 17. PMID 14730392.

References

Sources

* * * * Bonsdorff, B von: Diphyllobothriasis in Man. Academic Press, London, 1977 *Keas, B. E: Microscopy - Diphyllobothrium latum. Michigan State University, East Lancing, 1999

External links