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

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