Echinococcosis

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

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

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

  • Serology is somewhat more reliable for E multilocularis infections

  • May also distinguish the two major echinococcal infections

Imaging Studies

• Diagnosis usually based on imaging studies

  • Ultrasonography

  • CT

  • MRI

• In E granulosus infection, a large cyst containing multiple daughter cysts that fill the cyst interior is highly suggestive of diagnosis

• In E multilocularis infection, imaging shows an irregular mass often with areas of calcification

Medications

• Albendazole

  • Often used in conjunction with surgery

  • When used alone, 10–15 mg/kg/day orally has shown efficacy, with courses of 3 months or longer; alternating cycles of treatment and rest may be needed

• Mebendazole (40–50 mg/kg/day orally) is an alternative

• Praziquantel may also be effective

• In some cases, medical therapy is begun, with surgery performed if disease persists after some months of therapy

Surgery

• Treatment of cystic hydatid disease

  • Involves cautious surgical resection of cysts, with care not to rupture cysts during removal

  • Injection of a cysticidal agent is used to limit spread in the case of rupture

• Treatment of alveolar cyst disease

  • Generally relies on wide surgical resection of lesions

  • Therapy with albendazole before or during surgery may be beneficial and may also provide improvement or even cure in inoperable cases

Therapeutic Procedures

• Percutaneous aspiration, injection, and reaspiration (PAIR)

  • Can be used when cysts are inoperable

  • Patients receive antihelminthic therapy

  • Cyst is partially aspirated

  • Scolicidal agent (95% ethanol, hypertonic saline, or 0.5% cetrimide) injected after diagnostic confirmation

  • Risk of anaphylaxis is small; has been reported in about 2% of procedures, but death due to anaphylaxis has been rare

• Do not use PAIR if cysts communicate with biliary tract

Follow-Up

• Liver chemistry tests and complete blood counts should be monitored weekly when using albendazole

Prognosis

• About 15% of untreated patients eventually die because of the disease or its complications

• 90% of patients with nonresectable masses die within 10 years

• 25% recurrence rates after surgery

Prevention

• In endemic areas, prevention is by prophylactic treatment of pet dogs with 5 mg/kg of praziquantel at monthly intervals to remove adult tapeworms and by health education to prevent feeding of offal to dogs

When to Refer

• All patients

When to Admit

• Patients with symptomatic cysts

• Patients who will have percutaneous aspiration of cysts or surgery