Trematode flatworms Fasciola hepatica and F. gigantica .
Consumption of watercress or other aquatic plants contaminated with infective metacercariae; potentially in other ways, such as by ingestion of contaminated water.
F. hepatica is found in parts of the Americas, Europe, the Middle East, Africa, Asia, and Oceania, especially in areas where sheep or cattle are reared. F. gigantica has a more limited distribution (parts of Africa and Asia).
The acute phase of the infection (also known as the migratory, invasive, or hepatic phase) can last up to approximately 3–4 months. Although most infected people are asymptomatic during the acute phase, the clinical manifestations can include marked eosinophilia, fever, abdominal pain, other gastrointestinal symptoms, respiratory symptoms (such as cough), and urticaria. The chronic (biliary) phase begins when immature worms (larval flukes) reach the bile ducts; mature into adult worms, which may live up to a decade or longer; and start to produce eggs. The clinical manifestations, if any, during the chronic phase may reflect biliary tract disease (such as cholangitis, biliary tract obstruction, cholecystitis); pancreatitis also may occur.
Detection of eggs in stool or duodenal or biliary aspirates. Serologic testing may be useful during the acute phase (egg production does not start until at least 3–4 months after exposure, whereas parasite antibodies may become detectable within 2–4 weeks) and the chronic phase (particularly if egg production is intermittent or at low levels). Serologic testing is available through CDC (www.cdc.gov/dpdx; 404-718-4745; email@example.com). Imaging studies, such as ultrasonogram and CT of the hepatobiliary tract, may be helpful.
First-line treatment is with triclabendazole, which is not commercially available in the United States; it is available to US-licensed physicians through the CDC Drug Service, under a special protocol, which requires both CDC and FDA to agree that the drug is indicated for treatment of a particular patient (404-718-4745; firstname.lastname@example.org). Nitazoxanide therapy might be helpful in some patients. In some patients with biliary tract obstruction, removal of adult flukes (such as via endoscopic retrograde cholangiopancreatography) may be indicated.
Avoid eating uncooked aquatic plants, including watercress, especially from Fasciola -endemic grazing areas. See Chapter 2, Food & Water Precautions.
CDC website: www.cdc.gov/parasites/fasciola
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Barbara L. Herwaldt, Sharon L. Roy