Fascioliasis

Key Features

• Infection results from ingestion of encysted metacercariae on watercress or other aquatic vegetables or in water

• Eggs of worm infect snails; snails subsequently infect vegetation

• Most prevalent in sheep-raising countries, particularly where raw salads are eaten

Clinical Findings

• Symptoms related to migration of larvae present 6–12 weeks after ingestion

• Typical findings

  • Abdominal pain

  • Fever

  • Malaise

  • Weight loss

  • Urticaria

  • Eosinophilia

  • Leukocytosis

• Tender hepatomegaly and elevated liver function tests may be seen

• Migration to other organs may lead to localized disease (rare)

• Symptoms of worm migration subside after 2–4 months, followed by

  • Asymptomatic infection by adult worms

  • Intermittent symptoms of biliary obstruction, with biliary colic and, at times, findings of cholangitis

Diagnosis

• Eggs are not found in the feces during the acute migratory phase of infection

• Clinical suspicion should be based on clinical findings and marked eosinophilia in at-risk individuals

• Imaging studies

  • Show hypodense migratory lesions of the liver

  • In chronic infection, show masses obstructing extrahepatic biliary tract

• Serologic assays have sensitivity and specificity > 90%, but cannot distinguish past and current infection

• Antigen tests with excellent sensitivity and specificity are available in veterinary medicine and show promise in humans

• Definitive diagnosis is made by identifying eggs in stool

• Repeated examinations may be necessary

Treatment

• Praziquantel not effective

• Triclabendazole

  • Treatment of choice

  • Available in the United States through the CDC under an investigational protocol

  • Standard dosing of 10 mg/kg orally in a single dose or two doses over 12 hours achieves a cure rate of about 80%

  • Repeat dosing is indicated if abnormal radiologic findings or eosinophilia do not resolve

• Bithionol

  • Second-line drug

  • 30–50 mg/kg/day in three divided doses on alternate days for 10–15 days

  • Not available in the United States

• Treatment with either drug can be accompanied by abdominal pain and other gastrointestinal symptoms

• Other potential therapies

  • Emetine and dehydroemetine, both widely used in the past but quite toxic

  • Nitazoxanide

• Prevention of fascioliasis involves avoiding ingestion of raw aquatic plants