Echinococcus

Echinococcus

 

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

Epidemiology

  • Prevalence – endemic in Eurasia, South America and Africa
    • In North America – most cases occur in immigrants from endemic countries
  • Transmission – fecal-oral route

Organism

  • 3 species – E. granulosus, E. multilocularis and E. vogeli
  • The minute tapeworm, E. granulosus, develops in the intestine of dogs and other Canidae; prevalent where livestock are raised in association with dogs
  • Its larval stage, the hydatid cyst, may be found in many mammals (cattle, sheep, hogs, man) when the eggs are ingested
  • The adult worm is present only in dogs
  • Cysts develop in intermediate hosts (human, sheep, cattle, goats)
  • Hydatid cysts may form in any organ or tissue in humans; most commonly seen in the liver, lung and central nervous system
    • In humans, the embryo develops slowly into hydatid cysts, reaching a diameter of 1 cm in 5 months or so; at the end of 10 or more years, they may contain liters of fluid
    • The cysts vary considerably in size, depending on their age and location
      • Cysts 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

  • Hepatic disease is the most common presentation and may present as abdominal pain or a palpable right upper quadrant mass (about 2/3 of patients)
  • Lungs are the second most common site of involvement of cysts
  • Rupture of cysts leads to multifocal dissemination

Diagnosis

  • Indications for testing – clinical evidence by MRI/US may provide evidence for testing
  • Laboratory testing
    • Serum antibody screening
      • Positive antibody response occurs in 90% of liver cysts, but only in 50% of lung cysts
      • Most sensitive testing by ELISA and IFA methods
    • Diagnosis prior to any surgery is recommended; aspiration of cysts is discouraged since this may result in fluid leakage and dissemination

Treatment

  • Involves percutaneous aspiration, infusion of scolecoidal agents with reaspiration or surgery

Prevention

  • Strict dog-control programs in endemic areas