[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Cestodes (tapeworms)](https://durgical.com/en/microbiology/groups/cestodes/) › Hymenolepis nana

[Microbiology](https://durgical.com/en/microbiology/) · [Cestodes (tapeworms)](https://durgical.com/en/microbiology/groups/cestodes/)

# 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

## Key points

- The only human tapeworm that needs no intermediate host.
- Internal autoinfection.
- Egg with polar filaments.
- The most common tapeworm in children.
- Praziquantel.

## 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

- Eggs leave in stool already infective and survive only a few days outside.
- Once swallowed, the oncosphere enters an intestinal villus and forms a cysticercoid.
- The villus ruptures; the cysticercoid enters the lumen, attaches to the ileal mucosa and matures.
- The adult lives for weeks, but internal autoinfection keeps the infection going for years.
- 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:

- [Praziquantel](https://durgical.com/en/pharmacology/praziquantel/)

## Prevention

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

## In Colombia

It is the tapeworm most often found in stool exams of Colombian children, especially in day-care centres and institutions.

## Memory aid

Dwarf but stubborn: the dwarf tapeworm needs no one else and reinfects the child from the inside.

## 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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## Related

- [Taenia solium](https://durgical.com/en/microbiology/taenia-solium/)
- [Dibothriocephalus latus](https://durgical.com/en/microbiology/dibothriocephalus-latus/)
- [Echinococcus granulosus](https://durgical.com/en/microbiology/echinococcus-granulosus/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Cestodes (tapeworms)](https://durgical.com/en/microbiology/groups/cestodes/)

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](https://www.cdc.gov/dpdx/hymenolepiasis/index.html) (CDC, 2024); Parasitosis humanas (Corporación para Investigaciones Biológicas (CIB), 2019).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/hymenolepis-nana/