Echinococcus - Echinococcus Species

Diagnosis

Indications for Testing

  • Patient from endemic area with abdominal pain
  • Clinical evidence by MRI/ultrasound (US) may provide support for testing

Laboratory Testing

  • Diagnosis of Echinococcosis infection (CDC)
  • Serum antibody screening – ELISA, IFA, hemagglutination, latex agglutination
    •  ELISA and IFA – most sensitive testing methods
    • Positive antibody response occurs in 90% of liver cysts, but  only in 50% of lung cysts
  • Diagnosis recommended prior to any surgery
    • Aspiration of cysts for diagnosis is discouraged – may result in fluid leakage and dissemination

Imaging Studies

  • MRI/US – valuable in cyst detection 

Differential Diagnosis

Clinical Background

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

  • Three species – E. granulosus, E. multilocularis and E. vogeli
  • 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

  • Classic presentation – cysts in various organs
    • Almost exclusively pulmonary and hepatic cysts
      • Hepatic disease – most common presentation (~2/3 of patients)
        • May present as abdominal pain or a palpable right upper quadrant mass 
      • Lungs – second most common presentation
  • Rupture of cysts leads to multifocal dissemination

Prevention

  • Strict dog-control programs in endemic areas

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Echinococcus Antibody, IgG 2007220
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Confirm suspicion of Echinococcus parasite infection

Seroconversion between acute and convalescent sera considered strong evidence of recent infection

Patients with collagen vascular diseases, hepatic cirrhosis, schistosomiasis, and other parasitic infections may have false-positive results

Strong cross-reaction between echinococcosis and cysticercosis positive sera

Best evidence for infection is a significant change on two appropriately timed specimens where both tests are done in the same laboratory at the same time