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Microbiology · Cestodes (tapeworms)

Echinococcus granulosus !

  • Parasite
  • Exam priority: medium

A tiny dog tapeworm. If a person swallows its eggs, cysts grow for years in the liver or lung (hydatid disease).

Updated 2026-11-01

Also called: hydatid cyst, hydatid disease, Echinococcus vogeli (polycystic echinococcosis)

At a glance

Shape
Cyst with a laminated layer, germinal membrane, protoscolices and daughter cysts ('hydatid sand')
Family
Taeniidae
Type
Cestode (flatworm); humans host only the larval stage (hydatid cyst)
Size
Adult a few millimetres long in the dog; cyst several centimetres in humans

Morphology

  • The adult in the dog has only a few proglottids.
  • Egg indistinguishable from Taenia.
  • Unilocular hydatid cyst (E. granulosus) or multiple septate cysts (E. vogeli).

Transmission

  • Swallowing eggs from dog faeces: hands after petting dogs, contaminated water or vegetables.
  • Dogs become infected by eating raw offal with cysts.

Reservoir: Dogs and other canids (definitive host); Sheep, goats, cattle (intermediate hosts); E. vogeli: bush dog; pacas and agoutis as intermediate hosts

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. The dog carries the adult tapeworm in its gut and passes infective eggs in faeces.
  2. Sheep, goats or cattle swallow the eggs; the oncosphere crosses the gut and travels in the blood.
  3. In liver and lung it forms hydatid cysts that grow slowly and produce protoscolices.
  4. A dog is infected by eating raw offal with cysts; in 32–80 days it has adult tapeworms.
  5. Humans are accidental intermediate hosts: cysts form after swallowing eggs, and the cycle stops there.
  6. E. vogeli (South America): bush dog and paca or agouti; causes polycystic liver echinococcosis.

Virulence factors

  • The cyst grows slowly and compresses nearby organs.
  • If it ruptures, the fluid can cause anaphylaxis and seed new cysts.
  • Rupture into the bile duct causes jaundice and cholangitis; into a bronchus, expectoration of cyst contents.
  • E. vogeli behaves like a slow-growing liver tumour with secondary cysts.

Diseases it causes

Clinical picture

  • Silent for years; incidental finding on ultrasound.
  • Right upper quadrant mass or pain, hepatomegaly.
  • Cough, chest pain or haemoptysis with lung cysts.
  • Allergic reaction or anaphylaxis if the cyst ruptures.

Diagnosis

  • Ultrasound (the basis of the WHO stage classification), CT or MRI.
  • Serology (EIA or haemagglutination) confirmed by immunoblot; a negative result does not rule it out.
  • Cross-reaction with cysticercosis is possible.
  • Avoid blind puncture because of the risk of anaphylaxis and spread.

Treatment

By cyst stage: albendazole (benzimidazole), puncture-aspiration-injection-reaspiration (PAIR), surgery or watch-and-wait; albendazole is given around procedures and sometimes combined with praziquantel.

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

In Pharmacology:

Prevention

  • Deworm dogs regularly with praziquantel.
  • Do not feed raw offal to dogs; proper offal disposal at slaughterhouses.
  • Handwashing after contact with dogs.
  • EG95 vaccine for sheep where available.

Test yourself

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

What is the definitive host of Echinococcus granulosus?

Dogs and other canids, which carry the adult tapeworm in the gut.

Why is blind puncture of a hydatid cyst avoided?

Because rupture can cause anaphylaxis and seed new cysts.

Which test is the basis of cystic echinococcosis diagnosis?

Ultrasound, which also allows the cyst to be staged.

Which species causes polycystic echinococcosis in South America?

Echinococcus vogeli, with the bush dog as definitive host and the paca or agouti as intermediate hosts.

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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 - Echinococcosis (CDC, 2019); Echinococcosis (WHO, 2021).

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Representative model, for educational purposes only.