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Microbiology · Cestodes (tapeworms)

Hymenolepis nana !

  • Parasite
  • Exam priority: medium

The smallest and commonest tapeworm in children. It passes from person to person without another animal and can reinfect the same child from within.

Updated 2026-11-01

Also called: dwarf tapeworm

At a glance

Shape
Scolex with 4 suckers and a rostellum armed with one crown of hooks
Family
Hymenolepididae
Type
Cestode (flatworm), dwarf tapeworm
Size
Adult 1.5–4 cm

Morphology

  • Oval egg, 30–50 µm, with two membranes.
  • 4–8 polar filaments arise from the poles of the inner membrane: the diagnostic feature.
  • Six-hooked oncosphere; H. diminuta has larger eggs without filaments.

Transmission

  • Direct swallowing of eggs (dirty hands, contaminated food or water).
  • Internal autoinfection: eggs hatch inside the bowel.
  • Accidental swallowing of infected insects (grain beetles, fleas).

Reservoir: Humans; Rodents (closely related strains)

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. Eggs leave in stool already infective and survive only a few days outside.
  2. Once swallowed, the oncosphere enters an intestinal villus and forms a cysticercoid.
  3. The villus ruptures; the cysticercoid enters the lumen, attaches to the ileal mucosa and matures.
  4. The adult lives for weeks, but internal autoinfection keeps the infection going for years.
  5. Optional route: beetles or fleas can act as intermediate hosts if swallowed.

Virulence factors

  • Autoinfection allows very heavy worm loads.
  • Heavy loads inflame the mucosa, with abdominal pain and diarrhoea.
  • May add to poor appetite and low weight in children.

Diseases it causes

  • Hymenolepiasis: often asymptomatic; with heavy loads, abdominal pain, diarrhoea and poor appetite in children

Clinical picture

  • Found on a stool exam in an asymptomatic child.
  • Abdominal pain, diarrhoea, loss of appetite.
  • Clusters in day-care centres and institutions.

Diagnosis

  • Eggs with polar filaments on stool microscopy.
  • Concentration and repeated samples improve detection of light infections.

Treatment

Praziquantel is the drug of choice; nitazoxanide is an alternative.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Handwashing and short fingernails in children.
  • Safe water and sanitation.
  • Rodent and insect control in grain and food stores.

Test yourself

Think of the answer, then tap the question to see it.

What makes Hymenolepis nana unique among human tapeworms?

It can complete its cycle without an intermediate host, by direct egg ingestion and internal autoinfection.

Which egg feature identifies H. nana?

The 4–8 polar filaments arising from the inner membrane.

What is the drug of choice for hymenolepiasis?

Praziquantel.

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Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Hymenolepiasis (CDC, 2024); Parasitosis humanas (Corporación para Investigaciones Biológicas (CIB), 2019).

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Representative model, for educational purposes only.