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.
Also called: alveolar echinococcosis, alveolar hydatid disease, fox tapeworm, Echinococcus oligarthrus (unicystic Neotropical echinococcosis)
Quick facts
- Type
- Parasite · Cestodes (tapeworms)
- 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
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) →
- Neotropical unicystic echinococcosis from E. oligarthrus (extremely rare) Echinococcosis (hydatid disease) →
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:
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.
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.
Connections
← Back to the group: Cestodes (tapeworms)
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.