E. granulosus is common in sheep-raising areas of the Mediterranean, Middle East, Australia, New Zealand, South Africa, and South America. Dogs are the definitive hosts, which have adult tapeworms in their gastrointestinal tract, and herbivores (eg, sheep, horses, deer) or humans are intermediate hosts which develop cystic lesions in the liver or other organs. Foci also exist in regions of Canada, Alaska, and California.
Adult E. multilocularis worms are present in foxes, coyotes, and dogs, and the hydatid larvae occur in small wild rodents. Infected dogs are the primary link to occasional human infection. E. multilocularis occurs mainly in Central Europe, Alaska, Canada, and Siberia. Its range of natural infection in the continental US extends from Wyoming and the Dakotas to the upper Midwest.
Rarely, Echinococcus vogelii or Echinococcus oliganthus causes hydatid disease in humans, primarily in the liver. The disease may be polycystic (E. vogelii) or unicystic (E. oliganthus). These species occur in Central and South America.
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. No adult worms are 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. If a cyst in the liver leaks or ruptures, infection can spread to the peritoneum.
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. The cysts are not large, but they invade and destroy surrounding tissue and 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 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.
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 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 cystic (hydatid) echinococcosis in the liver, surgical resection plus albendazole for large or complicated cystic lesions judged to be active or transitional
Percutaneous aspiration followed by instillation of a scolicidal agent and reaspiration (PAIR), plus albendazole for small, active, or transitional cyst
Albendazole alone for unilocular, small, simple cysts judged to be active or transitional; and for inoperable lesions
Observation only for cysts categorized as inactive
For 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, sometimes via laparoscopy, can be curative. In some centers, percutaneous aspiration under CT guidance is done for small (<5 cm), unilocular simple cysts, followed by instillation of a scolicidal agent (eg, hypertonic saline) and reaspiration (PAIR [percutaneous aspiration-injection-reaspiration]). To prevent metastatic infections that can occur if cyst contents spill during the procedure or material is inadvertently left behind, albendazole is typically given one week before, during, and at least 4 weeks (up to 6 months depending on clinical and imaging response) after surgery or PAIR. The dose of albendazole is 400 mg orally 2 times a day (7.5 mg/kg 2 times a day in children up to a maximum of 400 mg 2 times a day). Albendazole used at this daily dose for several months without surgery can cure 30% of small, unilocular hydatid cysts. Albendazole at this dosage is the treatment of choice for inoperable cysts. Mebendazole 40 to 50 mg/kg body weight per day for several months is a second choice.
Patients with alveolar echinococcosis due to E. multilocularis should receive albendazole (in the above daily dosing used for cystic echinococcosis), and surgical resection is done at least one week after albendazole is started if feasible, which depends 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. It is important to monitor the complete blood count and liver enzymes during use.
Liver transplantation has been lifesaving in a few patients.
Echinococcosis occurs when ingested tapeworm eggs hatch, releasing oncospheres, which migrate into the liver or lungs or, less frequently, to the brain, bone, or other organs and develop into cysts; no adult worms are present in the gastrointestinal tract of humans.
The cysts of E. granulosus develop slowly (usually over many years) into large (up to 1 L), fluid-filled cysts (hydatid cysts), which contain numerous infective protoscolices.
Feces from infected dogs (and other canines) are the main source of human infection.
Liver cysts cause pain and sometimes jaundice; lung cysts can cause pain, cough, and hemoptysis.
E. multilocularis does not produce large cysts but invades and destroys surrounding tissue and can result in liver failure and death.
Diagnose by CT, MRI, or ultrasound, analysis of cyst fluid, and serologic testing.
Treatment varies depending on the infecting Echinococcus species, and the location, size, and imaging characteristics of the cysts, and may include surgery; or cyst aspiration, instillation of a scolicidal agent, and re-aspiration (PAIR); and prolonged treatment with albendazole.