[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/) › Echinococcus multilocularis and E. oligarthrus

# Echinococcus multilocularis and E. oligarthrus

- Parasite
- Exam priority: medium

A tiny fox tapeworm whose larva grows in the human liver like a slow cancer. Its cousin E. oligarthrus lives in wild cats of the Americas.

Updated Nov 13, 2026

Also called: alveolar echinococcosis, alveolar hydatid disease, fox tapeworm, Echinococcus oligarthrus (unicystic Neotropical echinococcosis)

## Quick facts

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

**Gram / shape**
Alveolar mass of many small vesicles

**Spread**
Swallowing eggs from the faeces of foxes

**Causes**
Alveolar echinococcosis

**Treatment**
Radical surgical resection when the lesion is confined

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- Life cycle
- In Colombia
- Memory aid
- What the colours mean

- Clinical Virulence factors
- Diseases it causes
- Clinical picture
- Diagnosis

- Treatment Treatment
- Prevention

- Study Test yourself

- Connections Connections

## Key points

- E. multilocularis = fox tapeworm, Northern Hemisphere.
- Alveolar echinococcosis grows like a liver cancer and metastasises.
- Fatal if untreated; radical surgery plus long-term albendazole.
- E. oligarthrus: wild felids, Central and South America, single cysts, extremely rare.
- Compare with E. granulosus (dog, unilocular cyst) and E. vogeli (bush dog, polycystic).

## At a glance

**Shape**
Alveolar mass of many small vesicles that buds outward and infiltrates tissue

**Family**
Taeniidae

**Type**
Cestode; humans host only the larval stage (metacestode)

**Size**
Adults 1.2–4.5 mm in the fox (E. oligarthrus up to 2.9 mm); liver lesions several centimetres

## Morphology

- The metacestode is a spongy mass of small vesicles without a clear outer wall.
- It grows by external budding, like a tumour, and can send fragments to distant organs.
- Eggs are identical to those of Taenia and E. granulosus.
- E. oligarthrus forms single cysts in its rare human cases.

## Transmission

- Swallowing eggs from the faeces of foxes, dogs or cats that have eaten infected rodents.
- Contaminated hands, wild berries, vegetables, soil or water.
- Dogs that hunt rodents bring the eggs close to people.

**Reservoir:** E. multilocularis: red and arctic foxes, also dogs, wolves and raccoon dogs (definitive hosts); voles and other rodents (intermediate); E. oligarthrus: wild Neotropical felids such as the puma, ocelot and jaguarundi; agoutis and other rodents (intermediate)

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- The adult lives in the small intestine of a fox or other canid and sheds eggs in its faeces.
- A vole or other rodent swallows the eggs; the larva settles mainly in the liver.
- There it forms a multivesicular mass full of protoscolices.
- A fox eats the rodent and adult worms mature in its gut within a few weeks.
- A person swallows eggs by accident and becomes a dead-end intermediate host.
- E. oligarthrus: same pattern between wild cats and rodents in Central and South America.

## Virulence factors

- The larva infiltrates the liver like a malignant tumour, destroying tissue and bile ducts.
- It can spread to nearby organs and metastasise to lungs, brain or bone.
- Silent for 5–15 years, so it is often found late.

## Diseases it causes

- Alveolar echinococcosis: tumour-like liver lesion, fatal if untreated [Echinococcosis (hydatid disease) →](https://durgical.com/en/conditions/echinococcosis/)
- Neotropical unicystic echinococcosis from E. oligarthrus (extremely rare) [Echinococcosis (hydatid disease) →](https://durgical.com/en/conditions/echinococcosis/)

## Clinical picture

- Long asymptomatic period, then right upper quadrant pain, weight loss and malaise.
- Obstructive jaundice from invasion of the bile ducts.
- Hepatomegaly with a hard, irregular liver; late liver failure.
- Often mistaken for liver cancer.

## Diagnosis

- Imaging: ultrasound, CT or MRI show an infiltrating, heterogeneous liver mass with calcifications.
- Serology: Em2 and Em18 antigen tests are sensitive and help follow treatment.
- Histology or PCR of resected tissue confirms it.
- Biopsy needs care because of the risk of spread.

## Treatment

Radical surgical resection when the lesion is confined, combined with long-term benzimidazoles (albendazole, or mebendazole), which are also used alone for inoperable disease; liver transplantation is an option in advanced cases.

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

In Pharmacology:

- [Albendazole](https://durgical.com/en/pharmacology/albendazole/)
- [Mebendazole](https://durgical.com/en/pharmacology/mebendazole/)

## Prevention

- Regular deworming of dogs and cats that hunt rodents, with praziquantel.
- Handwashing after contact with dogs or soil; wash wild berries and vegetables.
- Bait-based deworming of foxes has reduced the parasite in parts of Europe and Japan.

## In Colombia

Alveolar echinococcosis (E. multilocularis) is confined to the Northern Hemisphere and is not acquired in Colombia. In Colombia and South America the relevant forms are polycystic echinococcosis from E. vogeli and the very rare unicystic form from E. oligarthrus, linked to wild cats and rodents.

## Memory aid

Multi-locular means many rooms: the fox's tapeworm keeps building rooms in the liver, like a tumour that never stops renovating.

## Test yourself

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

## What are the definitive and intermediate hosts of Echinococcus multilocularis?

Foxes and other canids are definitive hosts; voles and other rodents are intermediate hosts.

## Why is alveolar echinococcosis compared with a malignant tumour?

Because the larva infiltrates the liver by external budding and can spread to distant organs.

## What is the treatment of alveolar echinococcosis?

Radical surgery when possible, combined with long-term albendazole; albendazole alone for inoperable disease.

## Which Echinococcus species has wild felids as definitive hosts in the Americas?

Echinococcus oligarthrus, with pumas, ocelots and other wild cats as definitive hosts.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/echinococcus-multilocularis-and-e-oligarthrus/)

## 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.

## Connections

## Related 3

- [Echinococcus granulosus](https://durgical.com/en/microbiology/echinococcus-granulosus/)
- [Taenia multiceps (coenurosis)](https://durgical.com/en/microbiology/taenia-multiceps/)
- [Taenia solium](https://durgical.com/en/microbiology/taenia-solium/)

## Related conditions 1

- [Echinococcosis (hydatid disease)](https://durgical.com/en/conditions/echinococcosis/)

[← 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 - Echinococcosis](https://www.cdc.gov/dpdx/echinococcosis/index.html) (CDC, 2019); [Echinococcosis](https://www.who.int/news-room/fact-sheets/detail/echinococcosis) (WHO, 2021).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/microbiology/echinococcus-multilocularis-and-e-oligarthrus/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/echinococcus-multilocularis-and-e-oligarthrus/