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Echinococcosis
is infection with larvae of Echinococcus
granulosus or E.
multilocularis (alveolar hydatid disease). Symptoms,
such as jaundice, abdominal discomfort, cough, chest pain, and hemoptysis,
arise from cysts in vital organs. Cyst rupture can cause fever,
urticaria, and serious anaphylactic reactions. Diagnosis is with
imaging tests, examination of cyst fluid, or serologic tests. Treatment
is with albendazole and/or surgery or cyst aspiration and instillation
of a scolicidal agent.
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 are found 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. On rare occasion, E. vogelii or E. oliganthus cause polycystic hydatid disease in humans, primarily in the liver.
Etiology
and Pathophysiology
Ingested eggs from animal feces (which may be present in the fur of dogs or other animals) hatch in the gut; 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 within or outside primary cysts. If the cyst 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 are found primarily in the liver but can metastasize to the lungs, lymph nodes, and other tissues.
Symptoms and Signs
Although many infections are acquired in 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. In the liver, they eventually produce abdominal pain or a palpable mass. Jaundice may occur if the bile duct is obstructed. Rupture into the bile duct, abdominal or peritoneal cavity, or lung may produce fever, urticaria, or a serious anaphylactic reaction. Pulmonary cysts are usually discovered on routine chest x-ray as round, often irregular, pulmonary masses. Pulmonary cysts can rupture, causing cough, chest pain, and hemoptysis.
Diagnosis
CT, MRI, and ultrasound scans 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) are variably sensitive but are useful if positive and should be obtained. Eosinophilia on CBC may be present.
Treatment
For E.
granulosis, albendazole 400 mg po bid for 1 to 6 mo (7.5 mg/kg bid in children) is curative in 30 to 40% of patients and can be used to suppress growth in inoperable cases. Surgery, sometimes via laparoscopy, can be curative. Albendazole is often given before surgery to prevent metastatic infections if there is spillage of cyst contents. Some centers perform percutaneous aspiration under CT guidance followed by instillation of a scolecocidal agent (eg, hypertonic saline) and re-aspiration (the PAIR technique—percutaneous aspiration-injection-reaspiration).
Prognosis for 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 the growth of inoperable lesions. Liver transplantation has been lifesaving in a few patients.
Last full review/revision November 2005
Content last modified November 2005
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