Echinococcus Species - Echinococcosis Infection

Echinococcosis infection is a zoonosis caused in humans by the larval stage of cestodes belonging to the genus Echinococcus.Imaging techniques, such as CT scans, ultrasonography, and MRIs, are used to detect cysts, suggestive of cystic echinococcosis. After a cyst has been detected, serologic tests may be used to confirm the diagnosis.

Diagnosis

Indications for Testing

  • Patient from endemic area with abdominal pain
  • Clinical evidence by magnetic resonance imaging (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

Background

Epidemiology

  • Incidence
    • Cystic disease
      • 1-200/100,000
      • Endemic in Eurasia, South America, and Africa
      • In North America, most cases occur in immigrants from endemic countries
    • Alveolar disease
      • 0.03-1.2/100,000
      • Restricted to northern hemisphere, particularly regions of China, Russian Federation, continental Europe, and North America
  • Transmission – fecal-oral route

Organism

  • 4 species in humans – E. granulosus, E. multilocularis, E. vogeli, E. oligarthus
    • ​E. granulosus (cystic) and E. multilocularis (alveolar) 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 liver, lung, and central nervous system (CNS)
    • 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
      • May contain liters of fluid after ≥10 years
      • May or may not be able to expand freely depending on location in body
      • In some cases, even a modest growth results in serious impairment to function of vital structures or 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

ARUP Laboratory Tests

Adjunct to other diagnostic tests (eg, imaging) for echinococcosis

Patient's travel history is necessary to aid in test interpretation

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

Best evidence for infection is a significant change on 2 appropriately timed specimens when both tests are performed in same laboratory at same time

Collagen vascular diseases, hepatic cirrhosis, schistosomiasis, and other parasitic infections can produce false-positive results

Strong cross-reaction between echinococcosis and cysticercosis positive sera

Medical Experts

Contributor

Couturier

Marc Roger Couturier, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Parasitology/Fecal Testing, Infectious Disease Antigen Testing, Bacteriology, and Molecular Amplified Detection, ARUP Laboratories
Contributor

Slev

Patricia R. Slev, PhD
Associate Professor of Clinical Pathology, University of Utah
Section Chief, Immunology; Medical Director, Immunology Core Laboratory, ARUP Laboratories

References

Additional Resources