What is Diphyllobothrium latum?

Diphyllobothrium latum and related species (the fish or broad tapeworm), the largest tapeworms that can infect people, can grow up to 30 feet long. Several other Diphyllobothrium species infect humans, but less frequently.
What are the signs and symptoms of Diphyllobothriuminfection?
Most infections are asymptomatic. However symptoms can include abdominal discomfort, diarrhea, vomiting, and weight loss. Vitamin B12 deficiency leading to pernicious anemia may occur. Complications include intestinal obstruction and gall bladder disease caused by migration of proglottids.
What should I do if I think I might be infected?
See your health care provider.
How is infection with Diphyllobothrium diagnosed?
Diagnosis is made by identification of eggs or segments of the tapeworm in a stool sample with a microscope. Eggs are usually numerous, but more than one stool sample may be needed to find them.
Is medication available to treat infection withDiphyllobothrium infection?
Yes, safe and effective medications are available to treatDiphyllobothrium infection (praziquantel or niclosamide are used most often).
How did I get infected with Diphyllobothrium?
You got infected by eating raw or undercooked fish. Examples of fish include salmon, trout, perch, walleyed pike, and other species -- usually freshwater fish. Some fish such as salmon live in both fresh and salt water and can harbor Diphyllobothrium larvae. Lightly salted, smoked, or pickled fish also may contain infectious organisms.
Who is at greatest risk of infection?
Diphyllobothrium infection generally occurs in the Northern Hemisphere (Europe, newly independent states of the Former Soviet Union, North America, Asia), but has been reported in Uganda and Chile. Fish infected with Diphyllobothrium larvae may be transported to and consumed in any area of the world.
How can I prevent Diphyllobothrium infection?
Do not eat raw or undercooked fish.
The FDA recommends the following for fish preparation or storage to kill parasites.

• Cooking
• Cook fish adequately (to an internal temperature of at least 145° F [~63° C]).
• Freezing
• At -4°F (-20°C) or below for 7 days (total time), or
• At -31°F (-35°C) or below until solid, and storing at -31°F (-35°C) or below for 15 hours, or
• At -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours.

Biology
Causal Agent:
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:

Immature eggs are passed in feces . Under appropriate conditions, the eggs mature (approximately 18 to 20 days)  and yield oncospheres which develop into a coracidia . After ingestion by a suitable freshwater crustacean (the copepod first intermediate host) the coracidia develop into procercoid larvae . 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 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 . 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 . 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 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)  and are passed in the feces . 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.