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Key Features

Essentials of Diagnosis

  • History of exposure to dogs or wild canines in an endemic area

  • Large cystic lesions, most commonly of the liver or lung

  • Positive serologic tests

General Considerations

  • The principal species that infect humans

    • Echinococcus granulosus, which causes cystic hydatid disease

    • Echinococcus multilocularis, which causes alveolar hydatid disease

  • Infection occurs when humans are intermediate hosts for canine tapeworms

  • Transmitted by ingesting food contaminated with canine feces containing parasite eggs

  • Eggs hatch in intestines to form oncospheres, which

    • Penetrate the mucosa

    • Enter the circulation

    • Encyst in specific organs as hydatid cysts

  • E granulosus forms cysts most commonly in the liver (65%) and in the lungs (25%)

  • However, cysts may develop in any organ, including

    • Brain

    • Bones

    • Skeletal muscles

    • Kidneys

    • Spleen

  • Cysts are most commonly single and can persist and grow slowly for many years

Demographics

  • E granulosus

    • Transmitted by domestic dogs in areas with livestock (sheep, goats, camels, and horses) as intermediate hosts

    • Endemic in Africa, the Middle East, southern Europe, South America, central Asia, Australia, New Zealand, and the southwestern United States

  • E multilocularis

    • Causes human disease much less commonly

    • Transmitted by wild canines

    • Endemic in northern forest areas of the northern hemisphere, including central Europe, Siberia, northern Japan, northwestern Canada, and western Alaska

  • An increase in the fox population in Europe has been associated with an increase in human cases

  • Other species that cause limited disease in humans are endemic in South America and China

Clinical Findings

Symptoms and Signs

  • Infections are commonly asymptomatic

  • Infections may be noted incidentally on imaging studies or present with symptoms caused by an enlarging or superinfected mass

  • Findings may include

    • Abdominal or chest pain

    • Biliary obstruction

    • Cholangitis

    • Portal hypertension

    • Cirrhosis

    • Bronchial obstruction leading to segmental lung collapse

    • Abscesses

  • Cyst leakage or rupture may be accompanied by a severe allergic reaction, including fever and hypotension

  • Seeding of cysts after rupture may extend the infection to new areas

  • E multilocularis generally causes a more aggressive disease than E granulosus, with initial infection of the liver, but then local and distant spread commonly suggests a malignancy

  • Obstructive findings in the liver and elsewhere develop with chronic infection

Differential Diagnosis

  • Amebic or pyogenic liver abscess

  • Malignant or benign tumor of liver or other involved organ

  • Fascioliasis (sheep liver fluke)

  • Clonorchiasis (Chinese liver fluke)

  • Choledocholithiasis

  • Congenital liver cyst or liver cyst associated with polycystic kidney disease

  • Cavitary pulmonary tuberculosis

  • Cysticercosis

Diagnosis

Laboratory Tests

  • Serologic tests

    • Include ELISA and immunoblot

    • Offer sensitivity and specificity over 80% for E granulosus liver infections, but lower sensitivity for involvement of other organs

    • May also distinguish the two major echinococcal infections

Imaging Studies

  • Diagnosis usually based on imaging ...

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