Microbiology & infectious diseases

Parasites-gastrointestinal (not liver)

Hymenolepis nana



Last author update: 1 January 2015
Last staff update: 5 October 2020

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PubMed Search: Hymenolepis nana[TI] full text[sb]

Haind Fadel, M.D.
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Cite this page: Fadel H. Hymenolepis nana. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/parasitologyhymenolepisnana.html. Accessed March 29th, 2024.
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

Cytology description
Cytology images

Contributed by Bobbi Pritt, M.D.

H. nana egg in stool specimen

H. nana and H. diminuta eggs



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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

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