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Echinococcosis is infection with larvae of Echinococcus granulosus or E. multilocularis (alveolar hydatid disease). Symptoms depend on the organ involved—eg, jaundice and abdominal discomfort with liver cysts or cough, chest pain, and hemoptysis with lung cysts. Cyst rupture can cause fever, urticaria, and serious anaphylactic reactions. Diagnosis is with imaging, examination of cyst fluid, or serologic tests. Treatment is with albendazole, surgery, or both or with cyst aspiration and instillation of a scolicidal agent.
Etiology
Echinococcus granulosus is common in sheep-raising areas of the Mediterranean, Middle East, Australia, New Zealand, South Africa, and South America. It requires canines as definitive hosts and herbivores (eg, sheep, horses, deer) or humans as intermediate hosts. Foci also exist in regions of Canada, Alaska, and California.
E. multilocularis worms are present in foxes, and the hydatid larvae occur in small wild rodents. Infected dogs and other canines are the main 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, E. vogelii or E. oliganthus causes polycystic hydatid disease in humans, primarily in the liver.
Pathophysiology
Ingested eggs from animal feces (which may be present in the fur of dogs or other animals) hatch in the gut. Larvae 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.
E. granulosus larvae develop 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.
Symptoms and Signs
Although many infections are acquired during childhood, clinical signs 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 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.
Diagnosis
Pulmonary cysts are usually discovered on routine chest x-ray as round, often irregular pulmonary masses.
CT, MRI, and ultrasound findings may be pathognomonic if daughter cysts and hydatid sand (protoscolices and debris) are present, but simple hydatid cysts may be difficult to differentiate from simple benign cysts, abscesses, or benign or malignant tumors. The presence of hydatid sand in aspirated cyst fluid is diagnostic.
Serologic tests (enzyme immunoassay, immunofluorescent assay, indirect hemagglutination assay) are variably sensitive but are useful if positive and should be done. CBC may detect eosinophilia.
Treatment
Surgery, sometimes via laparoscopy, can be curative. Albendazole is often given before surgery to prevent metastatic infections that can occur if cyst contents spill during the procedure. In some centers, percutaneous aspiration under CT guidance is done, followed by instillation of a scolicidal agent (eg, hypertonic saline) and reaspiration (PAIR [percutaneous aspiration-injection-reaspiration]).
For E. granulosis, albendazole 400 mg po bid for 1 to 6 mo (7.5 mg/kg bid in children up to a maximum of 400 mg bid) is curative in 30 to 40% of patients and can be used to suppress growth in inoperable cases.
Prognosis for patients with E. multilocularis infection is poor unless the entire larval mass can be removed. Surgery is indicated if it is feasible, which depends on the size, location, and manifestations of the lesion. Albendazole in the above doses can suppress growth of inoperable lesions. Liver transplantation has been lifesaving in a few patients.
Last full review/revision December 2009 by Richard D. Pearson, MD
Content last modified December 2009
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