Skip directly to search Skip directly to A to Z list Skip directly to site content
CDC Home
For questions about DPDx, contact us

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit


[Diphyllobothrium latum] [Diphyllobothrium spp.]

Eggs of D. latum. The opercula are open.

Eggs of Diphyllobothrium latum. The opercula are open.

Close-up of a few of the proglottids from the specimen in Figure A, showing the rosette-shaped uterus at the center of each proglottid.

Close-up of a few of the proglottids of Diphyllobothrium latum, showing the rosette-shaped uterus at the center of each proglottid.

Eggs of D. latum in a cross-section of a gravid proglottid, stained with hematoxylin-and-eosin (H&E).

Eggs of D. latum in a cross-section of a gravid proglottid, stained with hematoxylin-and-eosin (H&E).

Causal Agents

The cestode Diphyllobothrium latum (the fish or broad tapeworm), the largest human tapeworm. Several other Diphyllobothrium species have been reported to infect humans, but less frequently; they include D. pacificum, D. cordatum, D. ursi, D. dendriticum, D. lanceolatum, D. dalliae, and D. yonagoensis.

Life Cycle

Life cycle of Diphyllobothriasis

Immature eggs are passed in fecesthe number 1. Under appropriate conditions, the eggs mature (approximately 18 to 20 days)the number 2 and yield oncospheres which develop into a coracidiathe number 3. After ingestion by a suitable freshwater crustacean (the copepod first intermediate host) the coracidia develop into procercoid larvaethe number 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)the number 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 pikethe number 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 undercookedthe number 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 the number 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)the number 9 and are passed in the fecesthe number 1. 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.

Geographic Distribution

Diphyllobothriasis occurs in the Northern Hemisphere (Europe, North America, and Asia) and in South America (Uruguay and Chile). Freshwater fish infected with Diphyllobothrium sp. larva may be transported to and consumed in geographic areas where active transmission does not occur, resulting in human diphyllobothriasis. For example, cases of D. latum infection associated with consumption of imported fish have been reported in Brazil.

Clinical Presentation

Diphyllobothriasis can be a long-lasting infection (decades). Most infections are asymptomatic. Manifestations may include abdominal discomfort, diarrhea, vomiting, and weight loss. Vitamin B12 deficiency with pernicious anemia may occur. Massive infections may result in intestinal obstruction. Migration of proglottids can cause cholecystitis or cholangitis.

Back to Top

For questions about DPDx, contact us
  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
  • Notice: Linking to a non-federal site does not constitute an endorsement by HHS, CDC or any of its employees of the sponsors or the information and products presented on the site. The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO