Parasitology
Gastrointestinal (not liver)
Hymenolepis nana


Topic Completed: 1 January 2015

Revised: 5 February 2019

Copyright: (c) 2003-2019, PathologyOutlines.com, Inc.

PubMed Search: Hymenolepis nana[TI] full text[sb]
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Cite this page: Fadel H. Hymenolepis nana. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/parasitologyhymenolepisnana.html. Accessed February 18th, 2019.
Definition / general
  • Dwarf tapeworm (nanos means dwarf), up to 40 mm long; among the smallest and most common intestinal parasitic infections causing a public health threat worldwide, particularly among children
  • Most frequently recovered cestode species in US
Diagrams / tables

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Life cycle: Hymenolepis nana

Life cycle
  • Direct life cycle: through ingestion of infectious eggs
    • Eggs may be passed directly from person to person, usually by children
    • Eggs may be ingested in food, especially grain products contaminated by rodent droppings (parasite is common in mice)
  • Indirect life cycle: through ingestion of intermediate hosts (usually grain beetles) containing cysticercoid larvae; less common
  • After human ingestion, eggs hatch in intestine and embryos penetrate the mucosa, where they mature as cysticercoid larvae
  • Larvae subsequently emerge and reattach to the intestinal wall to complete their development into adult tapeworms in 2 - 3 weeks
  • Internal autoinfection: if eggs hatch shortly after being discharged from worm and rapidly invade the intestinal wall without leaving the body
Clinical features
  • Symptoms develop if large number of worms
  • May include abdominal pain, diarrhea, anorexia, irritability
Diagnosis
  • Recovery of oval, thin shelled, colorless eggs, 30 - 47 μm, from stool
  • Scolex has an armed rostellum
  • Proglottids have all of their genital pores located on same side of strobila
Case reports
Treatment
  • Praziquantel
Clinical images

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Large number of adult worms in colon

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Adults

Microscopic (histologic) images

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Morphological characteristics

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Eggs, various images

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Proglottids, various images

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Adults

Differential diagnosis
  • Other cestode worms