Diphyllobothriasis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Diphyllobothrium latum is usually transmitted via the feco-oral route to the human host. It reproduces in the small intestine of humans only. The gravid female worm lays eggs in the perianal area usually at night and causes pruritus. In addition to the fingernail contamination, the infective eggs can be transmitted via the dust and fomites.

Pathophysiology

Pathogenesis

Lifecycle

The lifecycle of Diphyllobothrium latum is completed in the human and marine host and comprises of the following stages:

Mode of Transmission

D. latum is transmitted via these modes:

Life cycle of Diphyllobothrium latum

Immature eggs are passed in feces 1 . Under appropriate conditions, the eggs mature (approximately 18 to 20 days) 2 and yield oncospheres which develop into a coracidia 3. After ingestion by a suitable freshwater crustacean (the copepod first intermediate host) the coracidia develop into procercoid larvae 4 . Following ingestion of the copepod by a suitable second intermediate host, typically minnows and other small freshwater fish, the procercoid larvae are released from the crustacean and migrate into the fish flesh where they develop into a plerocercoid larvae (sparganum) 5 . The plerocercoid larvae are the infective stage for 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, e.g., trout, perch, walleyed pike 6 . In this case, the sparganum can migrate to the musculature of the larger predator fish and humans can acquire the disease by eating these later intermediate infected host fish raw or undercooked 7 . After ingestion of the infected fish, the plerocercoid develop into immature adults and then into mature adult tapeworms which will reside in the small intestine. The adults of D. latum attach to the intestinal mucosa by means of the two bilateral groves (bothria) of their scolex 8 . The adults can reach more than 10 m in length, with more than 3,000 proglottids. Immature eggs are discharged from the proglottids (up to 1,000,000 eggs per day per worm) 9 and are passed in the feces 10 . Eggs appear in the feces 5 to 6 weeks after infection. In addition to humans, many other mammals can also serve as definitive hosts for D. latum.

Gallery

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  Illustration of the life cycle of Diphyllobothrium spp., the causal agents of Diphyllobothriasis. From Public Health Image Library (PHIL).

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  Diagram depicts the various stages in the life cycle of the tapeworm Diphyllobothrium latum, a cestode. From Public Health Image Library (PHIL).