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Hydatid disease is a zoonotic parasitic infection wherein humans are accidental intermediate hosts. It results from the ingestion of Echinococcus eggs shed in the feces of infected canines.

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https://www.youtube.com/watch?v=H6jrDC-JcrM

Etiopathogenesis

Causative organism:

• E. granulosus: Causes cystic echinococcosis, forms unilocular cysts, liver > lung
• E. multilocularis: Causes alveolar echinococcosis, more aggressive, behaves like malignancy

Transmission:

• Ingestion of ova → oncospheres penetrate intestine → hematogenous spread → hydatid cyst development in liver/lung/other organs.

Pathology

• Hydatid cysts are composed of three layers:
  • Pericyst (host fibrous reaction)
  • Ectocyst (acellular laminated membrane)
  • Endocyst (germinal layer with brood capsules/scolices)
• Cyst may contain daughter cysts and hydatid sand (free-floating protoscolices).

Clinical Features

https://www.youtube.com/watch?v=tKXnNFndESw

Depends on organ involved and cyst size:

• Liver (60–70%): RUQ pain, hepatomegaly, obstructive jaundice if cyst compresses bile ducts.
• Lung (20–30%): Cough, chest pain, hemoptysis, rupture into bronchus.
• Brain: Raised ICP, seizures.