Fun With Microbiology (What's Buggin' You?): Diphyllobothrium latum (revisited)

Diphyllobothrium latum (Helmith/Cestode)

Note: This post is entitled Diphyllobothrium latum "Revisited" as I posted a photo several years ago when a fixed film camera was the only tool in my arsenal. I'm sure you'll find these new photos superior. To visit the old post click below;

Diphylobothrium latum 2008

Known as ‘Fish Tapeworm’ or ‘Broad Tapeworm.

Disease: Causes’ Diphylobothriasis’. In some instances the infection can be relatively harmless while in others it results in an illness resembling pernicious anemia. The tapeworm may be depriving the infected host of vitamin B₁₂ as the adult worm contains a high concentration of this vitamin. Disease is acquired by eating raw or insufficiently cooked fish. Campers who cook their catch of fish over an open fire in the wild and cultures who eat raw or pickled (incomplete) fish may be more likely to acquire the infection. Lives in the proximal portion of the jejunum.

Geographic Distribution: Found in temperate regions with cold clear lakes. Prevalent in Japan, Russia, Scandinavia. Finland, the Baltics as well as Canada and Alaska. Has been found in the Great Lake Regions of the United States however is not considered to be endemic. In other regions of the world, different species of Diphyllobothrium may infect humans and susceptible mammals.

Life Cycle: Diphyllobothrium latum required two intermediate hosts in order to complete its life cycle. Briefly, the eggs are passed from feces which then hatch into small ciliated coracidium larvae. These coracidia survive until they are ingested by copepods where the second larval stage (procercoid) develops with growth. These fresh water crustaceans are themselves ingested by fish where they continue to grow where they develop into the plerocercoid stage. Small infected fish may not be suitable for human consumption however they in turn may be ingested by larger fish thereby infecting them. The larvae invades and resides in the flesh of the fish. As the larger fish consumes smaller infected fish, the infectious potential increases when consumed by humans. The plercoceroid larva (or sparganum) is not digested but remains in the small intestine where it develops to an adult tapeworm in about three to five weeks. The tapeworm, unless treated, may live for 25 years or longer.

Diagnosis: Infection with Diphyllobothrium latum is made by demonstrating the ova (eggs) in feces. Occasionally segments of the proglottids (broken off segments of the worm) can also be found in the feces.

Ova (Eggs): The Diphyllobothrium latum ova are ovoid in shape and have an operculum. (a small cover or hatch through which the larvae can escape). The yellowish-brown eggs are moderately thick-walled and are usually about 58 – 75 µm by 40 – 50 µm in size. They may have a small know at the end opposite of the operculum however it may be indistinct. The egg is unebryonated when passed in the feces.

Adult Worm: The clinical laboratory usually encounters the egg rather than the adult worm as it is the stool (feces) which is usually submitted for diagnosis. As I have no adult worm specimen, I’m unable to present any photos. Consult other sources for photos of the worm which may grow to 4 – 10 meters in length.

Two Diphyllobothrium latum eggs (arrows) in fecal concentrate (X100 Nikon)

Two Diphyllobothrium latum eggs in fecal concentrate (X250 Nikon)

Ditto

Diphyllobothrium latum egg. Arrows point to the the operculum or 'hatch' through which the larvae can escape. The protuberance, which can be somewhat inconspicuous, usually appears as a slight 'point' or 'bump' on the end opposite of the operculum. It is not evident on any of the photos in this post. It does appear in my 2008 D.latum post. Fecal concentrate. Click on photo to enlarge for better viewing.

(X250 Nikon - size differs from previous photos due to cropping)