Hydatid Disease (Echinococcosis)
Summary
Hydatid disease is a parasitic infection caused by the larval stage of the tapeworm Echinococcus granulosus (cystic echinococcosis) or E. multilocularis (alveolar echinococcosis). Dogs are the definitive host; sheep and cattle are intermediate hosts. Humans become accidental hosts by ingesting eggs from contaminated food or contact with dogs. Cysts form most commonly in the liver (70%) and lungs (20%), growing slowly over years. Cyst rupture can cause life-threatening anaphylaxis. Diagnosis is by imaging and serology. Treatment includes albendazole, PAIR procedure, or surgical excision depending on cyst characteristics.
Key Facts
- Organism: Echinococcus granulosus (cystic) or E. multilocularis (alveolar)
- Life Cycle: Dog (definitive) → Sheep/cattle (intermediate) → Humans (accidental)
- Sites: Liver (70%), Lung (20%), may affect any organ
- Key Risk: Cyst rupture → Anaphylactic shock
- Diagnosis: Ultrasound/CT + Serology
- Treatment: Albendazole, PAIR, or Surgery
Clinical Pearls
"Dog → Sheep → Human (Accidentally)": The classic cycle. Humans are dead-end hosts who get infected by ingesting eggs (usually from dog faeces).
"Rupture = Anaphylaxis": Cyst fluid is highly antigenic. Rupture (spontaneous or surgical) can cause life-threatening anaphylactic shock.
"Daughter Cysts Are Diagnostic": On imaging, seeing multiple daughter cysts within a larger cyst is virtually diagnostic of hydatid disease.
"Albendazole Pre-Op Is Essential": Always give albendazole before procedures to reduce viability of cyst contents and risk of dissemination.
Distribution
- Endemic in: Mediterranean, Middle East, South America, Central Asia, Australia, Africa
- Rural sheep-farming communities
Incidence
- 1-200 per 100,000 in endemic areas
- Rare in UK (imported or occupational)
Risk Factors
| Factor | Notes |
|---|---|
| Sheep farming | Close contact with dogs, sheep |
| Dog ownership | Dogs are definitive host |
| Rural living | Endemic regions |
| Poor hygiene | Faecal-oral transmission |
Life Cycle
- Adult tapeworm in dog intestine → Eggs shed in faeces
- Eggs ingested by intermediate host (sheep) or accidental host (human)
- Larvae penetrate intestinal wall → Portal circulation
- Cyst formation in liver, lung, or other organs
- Cyst growth slow (1-5cm/year); may reach massive size
- Cycle completes when dog eats infected sheep viscera
Cyst Structure
- Germinal layer: Inner; produces protoscoleces and daughter cysts
- Laminated layer: Middle; protective acellular layer
- Pericyst: Outer; host fibrous reaction
- Hydatid sand: Protoscoleces sediment at bottom
Why Anaphylaxis?
- Cyst fluid contains highly immunogenic proteins
- Leak or rupture exposes host to massive antigen load
- IgE-mediated immediate hypersensitivity
General
Liver Cysts (70%)
| Feature | Notes |
|---|---|
| Hepatomegaly | Palpable mass |
| RUQ pain/discomfort | Capsular stretch |
| Jaundice | Bile duct compression or rupture into biliary tree |
| Secondary infection | Resembles liver abscess |
Lung Cysts (20%)
| Feature | Notes |
|---|---|
| Cough | May be productive |
| Haemoptysis | If cyst ruptures |
| Chest pain | Pleuritic |
| Dyspnoea | Large cyst |
| Expectoration of cyst contents | "Grape skins" or salty taste |
Cyst Rupture
Liver Cyst
- Hepatomegaly
- Palpable mass (RUQ)
- Jaundice (if biliary involvement)
Lung Cyst
- Dullness to percussion
- Reduced breath sounds
- Signs of consolidation
Imaging
| Modality | Findings |
|---|---|
| Ultrasound | First-line for liver; sees cyst walls, daughter cysts, hydatid sand |
| CT | Better anatomical detail; surgical planning |
| CXR | Lung cysts; round well-defined mass |
| MRI | Complex cysts, biliary/vascular involvement |
WHO Ultrasound Classification (CE1-CE5)
- CE1-CE2: Active cysts
- CE3: Transitional
- CE4-CE5: Inactive/calcified
Serology
- Echinococcus IgG (ELISA, IHA)
- Sensitivity 80-90% (liver); lower for lung
- Serology may be negative in encapsulated cysts
Other
- Eosinophilia (not always)
- LFTs (if biliary involvement)
Treatment Principles
┌──────────────────────────────────────────────────────────┐
│ HYDATID DISEASE MANAGEMENT │
├──────────────────────────────────────────────────────────┤
│ │
│ MEDICAL THERAPY: │
│ • Albendazole 400mg BD for 1-6 months │
│ • Used alone for small/multiple/inoperable cysts │
│ • Pre-/peri-operative cover (reduces recurrence) │
│ │
│ PAIR PROCEDURE (Percutaneous): │
│ • Puncture, Aspirate, Inject scolicidal agent, │
│ Re-aspirate │
│ • For CE1-CE3 cysts, >5cm │
│ • Albendazole 4 days before and 1 month after │
│ │
│ SURGERY: │
│ • For complicated cysts, biliary involvement, │
│ lung cysts, large cysts │
│ • Options: Cystectomy, pericystectomy, hepatectomy │
│ • Scolicidal agent to sterilise field │
│ • Albendazole cover essential │
│ │
│ WATCH & WAIT: │
│ • CE4-CE5 (inactive, calcified cysts) │
│ • Monitor only │
│ │
│ ⚠️ Anaphylaxis kit must be available for PAIR/surgery │
│ │
└──────────────────────────────────────────────────────────┘
Scolicidal Agents
- Hypertonic saline (20%)
- Ethanol (95%)
- Cetrimide
Of Disease
- Anaphylactic shock (rupture)
- Secondary infection (pyogenic abscess)
- Biliary fistula
- Dissemination (secondary echinococcosis)
- Mass effect (organ dysfunction)
Of Treatment
- Anaphylaxis (PAIR/surgery)
- Cyst recurrence
- Biliary leak (surgery)
With Treatment
- 90%+ cure rate with appropriate treatment
- Recurrence 2-25% depending on approach
Without Treatment
- Cysts grow slowly
- May remain asymptomatic for years
- Risk of complications increases with size
Key Guidelines
- WHO: Expert Consultation on Echinococcosis
- WHO-IWGE Cyst Classification
Key Evidence
PAIR
- Effective for selected cysts; lower morbidity than surgery
Albendazole
- Essential adjunct; reduces recurrence
What is Hydatid Disease?
Hydatid disease is an infection caused by a tapeworm called Echinococcus. Dogs carry the adult worm in their gut, and humans can get infected by accidentally swallowing the eggs, usually through contact with infected dogs or contaminated food.
What Happens?
The eggs hatch in the gut and travel to the liver or lungs, where they form fluid-filled cysts. These cysts grow slowly and may not cause symptoms for years.
Is it Dangerous?
The main danger is if a cyst ruptures. This can cause a severe allergic reaction (anaphylaxis). Large cysts can also cause problems by pressing on other organs.
How is it Treated?
- Medication: Albendazole (antiparasitic drug)
- Drainage procedure: PAIR (draining and treating the cyst through a needle)
- Surgery: For large or complicated cysts
Primary Guidelines
- WHO. Echinococcosis Fact Sheet. who.int
Key Studies
- Brunetti E, et al. Expert consensus for the diagnosis and treatment of cystic and alveolar echinococcosis. Acta Trop. 2010;114(1):1-16. PMID: 19931502