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Diphyllobothrium (fish tapeworm)
Epidemiology:
1) widely distributed in temperate zones
a) especially northern Europe, Scandinavia, Russia & Japan
b) in North America Canada, north central states, Pacific coast states & Alaska
2) definitive hosts include piscivorous mammals & possibly birds
3) eggs passed unembryonated in the feces must reach a fresh water stream or lake to continue development
4) after several weeks of embryonation in fresh water, a ciliated larval form with 6 hooks (coracidium) hatches & is ingested by a copepod
5) the coracidium develops into a procercoid larva which is infective for a 2nd intermediate host, a fish
6) in fish, the procercoid migrates into the tissues & develops into a plerocercoid larva
7) plerocercoids may be passed up the food chain unchanged & accumulate in larger fish
8) human acquire Diphyllobothrium infection by ingestion of raw or inadequately cooked fish (containing infectious plerocercoids) that have spent at least part of their life in fresh water
Pathology:
1) adults mature & initiate egg production in approximately 1 month
2) eggs passed unembryonated in the feces
Clinical manifestations:
1) may be asymptomatic
2) passage of a length of strobila in the feces is often the presenting complaint
3) abdomonal discomfort & diarrhea may be present
Complications:
1) intestinal obstruction (rare)
2) vitamin B12 deficiency with megaloblastic anemia
Laboratory:
1) diagnosis is made by finding brown, oval-shaped operculate eggs in feces
2) eggs measure 58-76 by 40-52 um
4) a length of strobila or intact worm passed in the feces allows identification of species
a) scolex is elongated with longitudinal grooves (bothria) which replace suckers
b) gravid proglottids are wider than they are long with genital pores located midventrally adjacent to a rosette-shaped uterus
5) serum vitamin B12
Management:
1) praziquantel 10-20 mg/kg PO once
2) niclosamide 2 g PO once
3) vitamin B12 IM if B12-deficient
4) prevention
a) heating fish to > 54 degrees C for 5 minutes
b) freezing to < -18 degrees C for 24 hours
Related
coracidium
niclosamide (Niclocide, Clonitralid, Bayluscide)
operculate
piscivorous
plerocercoid
praziquantel (Biltricide)
procercoid
strobila
Specific
Diphyllobothrium latum (fish tapeworm)
Diphyllobothrium spirometra
General
Cestoda (tapeworm)
Properties
KINGDOM: animal
PHYLUM: helminth
References
- Clinical Diagnosis & Management by Laboratory Methods,
19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia,
PA. 1996, pg 1289
- Harrison's Principles of Internal Medicine, 13th ed.
Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 933
- Grimm L
What's Eating You: 12 Common Intestinal Parasites.
Medscape. November 25, 2019
https://reference.medscape.com/slideshow/intestinal-parasites-6010996