Echinococcosis

Human echinococcosis, also known as hydatidosis or hydatid disease, is a parasitic disease caused by small tapeworms of the genus Echinococcus. The two most common forms of hydatidosis are cystic echinococcosis (CE), caused by E. granulosus, and alveolar echinococcosis (AE), caused by E. multilocularis. Infection occurs by ingesting Echinococcus eggs, most commonly via hand-to-mouth transmission or through food, water, or soil contaminated with feces. Following a long incubation period, infection with E. granulosus typically results in the formation of a single liver cyst (hydatid cyst), which may be asymptomatic or cause upper abdominal pain and other GI complaints. In contrast, infection with E. multilocularis resembles a hepatic malignancy that invades and destroys the surrounding tissue, which can lead to complications such as portal hypertension, cholangitis, jaundice, and even cirrhosis. Other extrahepatic manifestations may also occur as a result of metastasis to distant sites. Because of its malignant nature, AE is more difficult to treat and has a much higher mortality rate than CE. Treatment for both diseases consists of antihelminthic agents (e.g., albendazole or mebendazole), often in combination with surgical intervention.

• Pathogens: Echinococcus tapeworms ^[1][2]
  • Echinococcus granulosus causes CE
  • Echinococcus multilocularis causes AE
• Transmission
  • Hand-to-mouth
    • From the fur of definitive hosts (e.g., petting a dog or cat)
    • Contaminated dirt (e.g., dog feces) ^[1]
  • Fecal-contaminated food or water (e.g., wild berries, mushrooms) ^[1]

• Hosts ^[1]
  • Definitive hosts: foxes, dogs, and cats
  • Intermediate hosts: hoofed animals; (e.g., sheep, goats, camels, horses, cattle, and pigs)
  • Humans are accidental hosts (e.g., sheep farmers)
• Life cycle: : The definitive host consumes hydatid cysts from an intermediate host → adult tapeworms develop and inhabit the small intestine → tapeworms produce eggs that are shed through stool, contaminating the ground → eggs are ingested by intermediate hosts → eggs hatch within the intestine and penetrate the intestinal wall → travel through the bloodstream and lymphatic system → liver or other organs → hydatid cysts ^[1]

Cyst rupture may lead to a severe allergic reaction and even death.

Echinococcus granulosus (cystic echinococcus): singular hydatid cyst; Echinococcus multilocularis (alveolar echinococcosis): infiltrative growth.

Suspected echinococcosis is generally confirmed via ELISA and ultrasonography.

• Laboratory tests: (nonspecific; low diagnostic value): mild eosinophilia, leukopenia or thrombocytopenia, liver function abnormalities
• Serology: positive ELISA (false negatives are common)
• Imaging
  • Ultrasonography
    • Cystic echinococcosis: unilocular, anechoic, smooth, well-defined hepatic cyst with or without daughter cysts
      • Possibly daughter cysts and hyperdense internal septa
      • Eggshell calcifications within the wall of a hydatid cyst may be visible
    • Alveolar echinococcosis: lesions with irregular, poorly defined margins, central necrosis, and irregular calcifications within the cyst and cyst wall
  • CT scan: indicated for further evaluation of cysts
    • Alveolar echinococcosis usually not well-defined, but shows infiltration of the liver and surrounding tissue
    • Best test for evaluating extrahepatic cysts

Cystic echinococcosis

• Observation: inactive cyst with heterogeneous hypoechoic/hyperechoic contents, or solid, calcified wall
• Medical therapy: may be considered as the sole treatment for cysts < 5 cm
  • Drug of choice: albendazole
  • Alternative drugs: mebendazole, praziquantel
• Ultrasonography/CT-guided percutaneous drainage
  • Commonly conducted using the PAIR (puncture, aspiration, injection , reaspiration) procedure
  • Should only be done in combination with medical therapy (albendazole)
  • Indications: > 5 cm and/or septations
• Surgery
  • Goal: resect the whole cyst to prevent spillage of its content
  • Indications: > 10 cm, complicated cysts
• Follow-up: Because relapse is common, patients should be closely monitored via imaging for up to five years.

Any invasive procedure (drainage or surgery) of hydatid cysts should be performed with the utmost care to prevent spillage of cyst contents, which could cause life-threatening anaphylactic shock and/or secondary seeding of infection!

Alveolar echinococcosis

• Curative resection followed by at least 2 years of treatment with albendazole to prevent a potential relapse
• Palliative care if surgery is not possible or unsuccessful: see “Medical therapy” above
• Follow-up for at least 10 years

• Cystic echinococcosis: the long-term outcome depends on organ manifestation
• Alveolar echinococcosis: 90% of patients die within 10 years if left untreated. However, patients who receive treatment have a life expectancy only 2–3 years lower than the general population. ^[3]