Extraintestinal Cestodes and Blood Trematodes

• Echinococcus spp.


  Belong to the Family Taeniidae, Order Cyclophyllidea
• HUMAN ECHINOCOCCOSIS is regarded as an emerging/re-emerging zoonotic disease
• Echinococcosis is acquired when the eggs of this parasite are ingested

  
• Echinococcus species of public health importance

  • E. granulosus
  • E. multilocularis
  • E. vogeli
  • E. oligarthrus
• E. granulosus


  Causes CYSTIC ECHINOCOCCOSIS
• E. multilocularis


  Causes ALVEOLAR ECHINOCOCCOSIS
• E. vogeli and E. oligarthrus

  Both cause POLYCYSTIC ECHINOCOCCOSIS
• E. multilocularis, E. vogeli, and E. oligarthrus are less common because their life cycles are sylvatic
• Echinococcus multilocularis


  Also known as the "FOX TAPEWORM"

  
• Echinococcus multilocularis causes parasitic tumors found in the liver, lungs, brain, and other organs
• Echinococcus multilocularis infection is fatal if left untreated
• Cysts of E. multilocularis

  Called Multilocular/alveolar cysts
• Echinococcus granulosus


  Also known as the "DOG TAPEWORM or HYDATID TAPEWORM"

  
• Echinococcus granulosus is the shortest tapeworm

  
• Echinococcus granulosus


  Causes CYSTIC ECHINOCOCCOSIS, the most common presentation of echinococcal infection in humans

  
• Adult worms of E. granulosus


  Inhabit the small intestines of canines

  
• Cysts of E. granulosus

  Called Unilocular hydatid cyst
• As the unilocular cyst of E. granulosus develops, inflammatory reactions may occur in surrounding tissues
• Infection with E. granulosus leads to down-regulation of inflammatory cytokines, resulting in local immunosuppression
• The mass effect brought about by the enlarging E. granulosus cyst results in organ impairment as the neighboring tissues undergo atrophy and tissue necrosis
• Humans


  Accidental host for Echinococcus spp.

  
• Adult worm appearance


  • Scolex: pyriform with short neck, 4 acetabula
  • Rostellum: 30-36 hooks
  • Length: 3-6mm
  • Strobila: 3 proglottids (immature, mature, gravid)
  • Uterus: midline, with lateral evaginations, filled with eggs resembling other taeniid worms
  • Habitat: Small intestine of Canines

  
• Ova


  Identical to Taenia, accidentally ingested by humans
• Hydatid cysts


  Larval stage, diagnostic stage, found in human tissues, formed through central vesiculation, uniocular/granular, size: 1-7cm and grows 1-5cm per year

  
• Brood capsules


  Rupture and release protoscolices
• Hydatid sand


  Composed of protoscolices and brood capsules outside the cyst
• Hosts of Echinococcus spp.

  • Definitive host: Dogs
  • Intermediate host: Goats, Horse, Camels, Sheep
  • Accidental host: Humans

  
• Life cycle of Echinococcus spp.

  1. Eggs swallowed by intermediate host

  2. Eggs hatch in duodenum and release oncospheres

  3. Oncospheres penetrate intestinal wall and migrate to organs/tissues

  4. Oncospheres develop into cysts (hydatid cyst)

  5. Cysts in tissues ingested by carnivores/omnivores

  6. Protoscolices evaginate and attach to intestinal wall of definitive host, developing to adults

  7. Adults release eggs passed out in stool

  
• Cystic echinococcosis is caused by the developing larval cyst in tissues of the intermediate host
• Organs commonly involved in human cystic echinococcosis

  • Liver (most common, 70% of cases, 85% in right lobe)
  • Lungs (20-30% of cases)
  • Brain (10% of cases together with orbit)
  • Orbit
• Cysts may rupture and cause metastasis
• Hepatic cysts are mostly found in the inferior right lobe, and may present as hepatic enlargement, right epigastric pain or jaundice
• Abdominal cysts may cause discomfort when large enough
• Peribronchial cysts may discharge into a bronchus and result in sudden coughing accompanied by allergic symptoms, with sputum containing frothy blood, mucus, hydatid fluid, and bits of membrane
• Cysts in the brain may cause increased intracranial pressure and Jacksonian epilepsy
• Cysts in the kidneys may cause intermittent pain, hematuria, kidney dysfunction, and hydatid material in the urine
• Rupture of a hepatic cyst into the biliary duct produces a characteristic triad of findings: intermittent jaundice, fever, and eosinophilia
• Diagnostic tests for echinococcosis

  • Radiography & Ultrasonography
  • Indirect Hemagglutination (IHA)
  • Indirect Fluorescence Antibody (IFA)
  • Enzyme Immunoassays (EIA)
  • ELISA/ IMMUNOBLOT
  • Casoni test
  • Anti-P1 antibodies
• ELISA/IMMUNOBLOT is the current gold standard serology for human cystic echinococcosis
• Treatment options for echinococcosis

  • Surgical resection (for large cysts >10cm)
  • Chemotherapy with benzimidazole compounds (Albendazole & Mebendazole, for small cysts <7mm)
  • Percutaneous aspiration, injection, re-aspiration (PAIR) (for multiple cysts)