Echinococcus

• Echinococcus spp.

  Emerging/reemerging zoonotic disease caused by the larval stage of the parasite

  
• Echinococcus spp.

  • Common species: E. granulosus (Cystic echinococcosis)

  Less common species: E. multilocularis (alveolar echinococcosis), E. vogeli, E. oligarthrus

  
• Echinococcus spp. is not common in the Philippines, but occurrence is not uncommon as well
• Definitive host

  • Dogs and Canines
• Intermediate host

  • Sheep, goat, swine, camel, horses, humans
• Humans are accidental hosts for Echinococcus spp.

  
• Infective stage to canines

  Hydatid cyst (larval stage: protoscolices)

  
• Adult Echinococcus

  • Habitat: Small intestine of canines

  Size: 3 - 6 mm in length

  Structure: Scolex, Neck, Strobila (three proglottids)
• Scolex

  • Pyriform shape

  Four acetabula, armed with two circular rows of 30 - 36 hooklets
• Proglottids

  • One immature,
  • one mature,
  • one gravid: Widest and longest proglottid, Uterus is midline, lateral evaginations, filled with eggs
• Hydatid cyst

  • Spherical in shape

  Contains protoscolices (infective larvae)

  Layers: Outer pericyst, Middle laminated membrane, Inner germinal layer

  Hydatid sand: Found in older cyst that contains granular materials of free protoscolices, daughter cyst

  
• Ova

  Similar with Taenia spp. ova
• Life cycle of Echinococcus spp.

  Definitive host has adult Echinococcus in small intestine, gravid proglottid is released in environment, releasing eggs which hatch to release oncosphere when ingested by intermediate host

  Oncosphere penetrates walls of small intestine and migrates in different parts of intermediate host body

  Intermediate host is eaten by canines, releasing protoscolices from cyst in meat

  Protoscolices mature in definitive host, become gravid and release eggs

  Eggs ingested by humans, hatch releasing oncosphere that penetrates small intestine and migrates to other parts of accidental/dead-end host, oncosphere matures into hydatid cyst
• Echinococcosis or Hydatidosis


  Disease caused by Echinococcus spp.

  
• Human cystic echinococcosis


  • Developing larval cyst in tissues of intermediate host

  Most common site: Liver (70% of cases, 85% in right lobe, commonly inferior, cause of partial liver necrosis)

  Other sites: Lungs (20-30% of cases), Brain, orbit (10% of cases)

  
• E. granulosus

  Causes unilocular hydatid cyst
• E. multilocularis

  Causes alveolar cysts
• Echinococcosis or Hydatid disease

  • Mechanical effects of hydatid cyst drives patients to seek medical intervention and/or diagnosis

  Slow growing, parasite may be acquired during childhood but often diagnosed during adulthood

  Brain involvement: Increased intracranial pressure and seizure

  If hepatic hydatid cyst ruptures into biliary duct: Intermittent jaundice, fever, eosinophilia

  Primary cyst rupture can cause anaphylaxis, which is lethal

  Rupture may be caused by coughing, muscle strain, trauma, and even surgery

  Protoscolices may metastasize into other areas forming secondary cysts

  
• Diagnosis


  • Radiographic

  Serologic
• Treatment

  • Surgical resection (preferred if large liver cyst, secondary infection, or cyst in extrahepatic sites)

  Percutaneous Aspiration, Injection, and Reaspiration (PAIR)

  Chemotherapy (Mebendazole or Albendazole for <7 mm in diameter, isolated cyst, uncomplicated cyst, patients with negative serology)

  PAIR plus Mebendazole or Albendazole (greater efficacy, lower morbidity and mortality)