Echinococcosis

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

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