Bad Bug Book:
Foodborne Pathogenic Microorganisms and Natural Toxins Handbook
Diphyllobothrium latum and other members of the genus are broad fish tapeworms reported from humans. They are parasitic flatworms.
Diphyllobothriasis is the name of the disease caused by broad fish tapeworm infections.
Diphyllobothriasis is characterized by abdominal distention, flatulence, intermittent abdominal cramping, and diarrhea with onset about 10 days after consumption of raw or insufficiently cooked fish. The larva that infects people, a "plerocercoid," is frequently encountered in the viscera of freshwater and marine fishes. D. latum is sometimes encountered in the flesh of freshwater fish or fish that are anadromous (migrating from salt water to fresh water for breeding). Bears and humans are the final or definitive hosts for this parasite. D. latum is a broad, long tapeworm, often growing to lengths between 1 and 2 meters (3-7 feet) and potentially capable of attaining 10 meters (32 feet); the closely related D. pacificum normally matures in seals or other marine mammals and reaches only about half the length of D. latum. For treatment please see http://www.dpd.cdc.gov/dpdx/HTML/Frames/A-F/Diphyllobothriasis/body_Diphyllobothriasis_page2.htm
The disease is diagnosed by finding operculate eggs (eggs with a lid) in the patient's feces on microscopical examination. These eggs may be concentrated by sedimentation but not by flotation. They are difficult to distinguish from the eggs of Nanophyetus spp..
The larvae of these parasites are sometimes found in the flesh of fish.
Diphyllobothriasis is rare in the United States, although it was formerly common around the Great Lakes and known as "Jewish or Scandinavian housewife's disease" because the preparers of gefillte fish or fish balls tended to taste these dishes before they were fully cooked. The parasite is now supposedly absent from Great Lakes fish. Recently, cases have been reported from the West Coast.
In persons that are genetically susceptible, usually persons of Scandinavian heritage, a severe anemia may develop as the result of infection with broad fish tapeworms. The anemia results from the tapeworm's great requirement for and absorption of Vitamin B12.
Consumers of raw and underprocessed fish are the target population for diphyllobothriasis.
Foods are not routinely analyzed for larvae of D. latum, but microscopic inspection of thin slices of fish, or digestion, can be used to detect this parasite in fish flesh.
An outbreak involving four Los Angeles physicians occurred in 1980. These physicians all consumed sushi (a raw fish dish) made of tuna, red snapper, and salmon. Others who did not consume the sushi made with salmon did not contract diphyllobothriasis. At the time of this outbreak there was also a general increase in requests for niclosamide from CDC; interviews of 39 patients indicated that 32 recalled consuming salmon prior to their illness.
For more information on recent outbreaks see the Morbidity and Mortality Weekly Reports from CDC.
Literature references can be found at the links below.
The FDA is determining whether the freezing recommendations (see chapter 25) for raw or semiraw seafood with anisakid nematodes will also prevent infections with the broad fish tapeworms.
Loci index for genome Diphyllobothrium spp.
Available from the GenBank Taxonomy database, which contains the names of all organisms that are represented in the genetic databases with at least one nucleotide or protein sequence.