Echinococcus Species - Echinococcosis Infection

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

• Hepatic mass
  • Infection
    • Entamoeba histolytica
    • Hepatic abscess
    • Mycobacterium tuberculosis
    • Intra-abdominal sepsis
    • Schistosoma spp
  • Hepatic cyst
  • Hepatocellular carcinoma
  • Budd-Chiari syndrome
  • Hemangioma
• Pulmonary mass
  • Infection – lung abscess
  • Lung tumor
  • Mycobacterium tuberculosis
• Central nervous system (CNS) mass
  • Brain tumor
  • Brain abscess
  • Taenia solium

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