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

• Hepatic mass
  • Entamoeba histolytica
  • Hepatic cyst
  • Inferior vena cava thrombosis
  • Liver abscess
  • Intra-abdominal sepsis
  • Budd-Chiari syndrome
  • Hepatocellular carcinoma
  • Schistosoma spp
• Pulmonary mass
  • Lung tumor
  • Lung abscess
• Central nervous system mass
  • Brain tumor
  • Brain abscess
  • Taenia solium

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