• Clinical science

Echinococcosis (Hydatidosis…)

Abstract

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.

Etiology

  • Pathogens: Echinococcus tapeworms
  • Transmission
    • Hand-to-mouth
      • From the fur of definitive hosts (e.g., petting a dog or cat)
      • Contaminated dirt (e.g., dog feces)
    • Fecal-contaminated food or water (e.g., wild berries, mushrooms)

References:[1][2][3]

Pathophysiology

Life cycle

  • 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)

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 systemliver or other organs → hydatid cysts

References:[1]

Clinical features

Features Cystic echinococcosis Alveolar echinococcosis
Incubation time
  • Up to 50 years
  • 5–10 years
Onset
  • Usually asymptomatic
  • Typically nonspecific symptoms
Hepatic
  • Single hepatic cyst (hydatid cyst)
  • HepatomegalyRUQ pain
  • Malaise, nausea, vomiting
Extrahepatic
  • Primary involvement of other organs is very rare (< 1% of cases)
  • Metastasis to other organs (especially lungs, brain, spleen) in ∼ 13% of cases

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!

References:[4]

Diagnostics

Suspected echinococcosis is generally confirmed via ELISA and ultrasonography.

References:[4][3][5]

Treatment

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, respiration) procedure
    • Should only be done in combination with medical therapy (albendazole)
  • 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

References:[6]

Prognosis

  • 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.

References:[4]