Echinococcus Species

Echinococcosis infection is a zoonosis caused in humans by the larval stage of cestodes belonging to the genus Echinococcus.

Epidemiology

• Incidence – 1-200/100,000 for cystic disease; 0.03-1.2/100,000 for alveolar disease
  • Endemic in Eurasia, South America, and Africa
  • In North America, most cases occur in immigrants from endemic countries
• Transmission – fecal-oral route

Organism

• Four species in humans – E. granulosus, E. multilocularis, E. vogeli, E. oligarthus
  • ​E. granulosus and E. multilocularis most common
• Minute tapeworm, E. granulosus, develops in the intestine of dogs and other Canidae
  • Prevalent where livestock raised in association with dogs
  • Adult worm present only in dogs
• Larval stage (hydatid cyst) – found in many mammals (eg, cattle, sheep, hogs, humans) when the eggs are ingested
• Cysts develop in intermediate hosts (eg, humans, sheep, cattle, goats)
• Hydatid cysts may form in any organ or tissue in humans – most commonly seen in the liver, lung, central nervous system
  • In humans, the embryo develops slowly into hydatid cysts
  • Cysts vary considerably in size, depending on their age and location
    • May reach a diameter of 1 cm in ~5 years
      • At the end of ≥10 years, may contain liters of fluid
    • May or may not be able to expand freely depending on the location in the body
    • In some cases, even a modest growth will result in serious impairment to the function of vital structures and even death

Clinical Presentation

• Initial phase – asymptomatic
• Classic presentation – cysts in various organs
  • Symptoms depend on cyst location(s)
  • Almost exclusively pulmonary and hepatic cysts (extrahepatic disease rare with E. multilocularis)
  • Hepatic disease – most common presentation
    • May present as abdominal pain or a palpable right upper quadrant mass
    • Significant symptoms unusual until cyst grows >10 cm
  • Lungs – second most common presentation
    • Cough, chest pain, hemoptysis
  • Other organs – heart, CNS, kidney, bone, ocular cysts
• Rupture of cysts leads to multifocal dissemination – patients may suffer fatal hypersensitivity reactions