Echinococcosis

Ingested eggs from animal feces (which may be present on the fur of dogs or other animals) hatch in the gut and release oncospheres (immature forms of the parasite enclosed in an embryonic envelope). Oncospheres penetrate the intestinal wall, migrate via the circulation, and lodge in the liver or lungs or, less frequently, in the brain, bone, or other organs. Adult worms are not present in the gastrointestinal tract of humans.

In tissue, E. granulosus oncospheres develop into cysts, which grow slowly (usually over many years) into large unilocular, fluid-filled lesions—hydatid cysts. Brood capsules containing numerous small infective protoscolices form within these cysts. Large cysts may contain > 1 L of highly antigenic hydatid fluid as well as millions of protoscolices. Daughter cysts sometimes form in or outside primary cysts. Cyst rupture releases cystic fluid and protoscolices into the surrounding body cavities and tissue, which can result in an immediate anaphylactic reaction. Released protoscolices can also invade new tissues to produce second-generation hydatid cysts.  

Echinococcus Life Cycle

Image

Image from the Centers for Disease Control and Prevention Image Library, Global Health, Division of Parasitic Diseases and Malaria.

E. multilocularis produces spongy masses that are locally invasive and difficult or impossible to treat surgically. Cysts occur primarily in the liver but can occur in the lungs, or other tissues, including the brain and bone marrow. The cysts are not large, but they invade and destroy surrounding tissue. Those in the liver can cause liver failure and death.

Although many infections are acquired during childhood, clinical signs of echinococcosis may not appear for years, except when cysts are present in vital organs. Symptoms and signs may resemble those of a space-occupying tumor.

Liver cysts may eventually cause abdominal pain or a palpable mass. Jaundice may occur if the bile duct is obstructed. Rupture into the bile duct, peritoneal cavity, or lung may cause fever, urticaria, or a serious anaphylactic reaction.

Pulmonary cysts can rupture, causing cough, chest pain, and hemoptysis.

• Imaging

• Serologic testing

• Examination of cyst fluid

CT, MRI, and ultrasound findings of the abdomen can be pathognomonic for cystic echinococcosis in the liver if daughter cysts and hydatid sand (protoscolices and debris) are present, but simple hydatid cysts may be difficult to differentiate from benign cysts, abscesses, or benign or malignant tumors. The presence of hydatid sand (scolices pass into the cyst fluid and form a white sediment) in aspirated cyst fluid is diagnostic. World Health Organization criteria use imaging results to categorize cysts as active, transitional, or inactive (1). Pulmonary involvement may present as round or irregular pulmonary masses on chest x-ray. Alveolar echinococcosis typically presents as an invasive mass.

Serologic tests (enzyme immunoassay, indirect hemagglutination assay) are sensitive in detecting infection, which can be confirmed by demonstrating echinococcal antigens using immunodiffusion (arc 5) or immunoblot assays. Complete blood count may detect eosinophilia.

• For hepatic echinococcosis, surgical resection

• Percutaneous aspiration followed by instillation of a scolicidal agent and reaspiration (PAIR)

• Albendazole alone or in combination with surgical resection or aspirationAlbendazole alone or in combination with surgical resection or aspiration

• Observation only

• For alveolar echinococcus, surgical resection, if possible, plus albendazoleFor alveolar echinococcus, surgical resection, if possible, plus albendazole

Treatment of cystic (hydatid) echinococcosis varies depending on the type, location, and number of cysts and whether imaging results indicate the cysts are active, transitional, or inactive (1).

Surgical resection can be curative and is the best treatment for complicated lesions with the following characteristics: ruptured cysts, cysts with biliary fistulae, cysts compressing vital structures, cysts with daughter cysts, cysts with a diameter > 10 cm, superficial cysts at risk of rupture due to trauma, and cysts accompanied by extrahepatic disease. For small (< 5 cm), unilocular simple cysts, some centers do percutaneous aspiration under CT guidance, followed by instillation of a scolicidal agent (eg, hypertonic saline) and reaspiration (PAIR [percutaneous aspiration-injection-reaspiration]). PAIR should not be performed for cysts where biliary communication is present, due to risk of cholangitis (2). To prevent metastatic infections that can occur if cyst contents spill during the procedure or material is inadvertently left behind, albendazole is typically given 1 week before, during, and at least 4 weeks (up to 6 months depending on clinical and imaging response) after surgery or PAIR (). To prevent metastatic infections that can occur if cyst contents spill during the procedure or material is inadvertently left behind, albendazole is typically given 1 week before, during, and at least 4 weeks (up to 6 months depending on clinical and imaging response) after surgery or PAIR (3).

Small, unilocular hydatid cysts may be treated with albendazole alone for several months' duration, resulting in about a 30% cure rate (Small, unilocular hydatid cysts may be treated with albendazole alone for several months' duration, resulting in about a 30% cure rate (4). Albendazole alone is also the treatment of choice for inoperable cysts. ). Albendazole alone is also the treatment of choice for inoperable cysts.

Observation only is an option for asymptomatic cysts that degenerate over time and are naturally inactivated. Imaging can show complete or near-complete egg shell calcification or a characteristic "ball of wool" appearance with iso-hyperechoic cyst content (stages CE5 and CE4, respectively).

Liver transplantation has been lifesaving in a few patients.

Prevention methods include public health education of sheep farmers and routine niclosamide administration for dogs that are in regular contact with sheep.

Patients with alveolar echinococcosis due to E. multilocularis should receive albendazole for ≥ 1 week followed by surgical resection when feasible (depending on the extent, location, and manifestations of the lesion). The prognosis is poor unless the entire larval mass can be removed. Albendazole is administered continuously for at least 2 years and patients are monitored for recurrence for 10 years or more thereafter. should receive albendazole for ≥ 1 week followed by surgical resection when feasible (depending on the extent, location, and manifestations of the lesion). The prognosis is poor unless the entire larval mass can be removed. Albendazole is administered continuously for at least 2 years and patients are monitored for recurrence for 10 years or more thereafter.

Prolonged, high-dose albendazole therapy can cause bone marrow suppression, liver toxicity, and temporary hair loss. Blood tests (a complete blood count and liver enzymes) should be monitored during albendazole therapy.Prolonged, high-dose albendazole therapy can cause bone marrow suppression, liver toxicity, and temporary hair loss. Blood tests (a complete blood count and liver enzymes) should be monitored during albendazole therapy.