Fasciola hepatica is a trematode liver fluke that infects primarily sheep, goats and cattle. The adult fluke is large, flat, brownish and leaf-shaped, and measures c. 2.5 × 1 cm. Large (140 × 75 µm) oval, yellow–brown, operculated eggs are excreted in the faeces of infected animals and hatch into ciliated miracidia in water. To be infective, the miracidium must first find its intermediate host, which is a freshwater snail. Multiplication takes place within the snail, and cercariae with unforked tails emerge. The cercariae encyst on aquatic vegetation and develop into the metacercarial stage. The metacercaria are then ingested by either normal hosts (sheep or cattle) or accidental hosts (humans). The metacercariae excyst in the intestine, perforate the intestinal wall, enter the peritoneum, and then pass through the liver capsule to enter the biliary tree. In the biliary tract, the mature fluke releases eggs, which are once again excreted in faeces to complete the life-cycle .
Human fascioliasis occurs worldwide, and there are significant numbers of patients in eastern Europe, Iran, northern Africa and South America . F. hepatica infection has two different stages with quite different signs and symptoms. The hepatic (first, acute or invasive) stage of the illness occurs when the organism perforates the liver and begins to migrate through the liver parenchyma towards the biliary radicles. The onset of this stage occurs 1–3 months following ingestion of metacercariae. Fever, urticaria, pain in the right hypochondrium, hepatomegaly, hypergammaglobulinaemia and marked eosinophilia are the classical signs and symptoms of this stage. Mild hepatitis, severe subcapsular haemorrhage and frank hepatic necrosis can also be observed. A combination of the symptoms of absolute eosinophilia, fever and right upper quadrant pain should bring to mind the possibility of F. hepatica infection. The second or biliary stage usually presents with intermittent right upper quadrant pain with or without cholangitis or cholestasis. Eosinophilia can also be detected [3–5].
There are many different methods for the diagnosis of F. hepatica infection. Stool examination for ova and parasites can be used, but is often unrevealing during the first stage. The method used most widely for diagnosis is an ELISA that detects antibodies against excretory–secretory antigen products from adult F. hepatica[6,7]. This assay has been shown to be rapid, sensitive and quantitative. Radiographic techniques such as computerised tomography (CT) and ultrasonography (US) are also used widely to aid and confirm the diagnosis. CT and US may also be used in follow-up to evaluate the efficacy of medical therapy. US seems to be more useful in the biliary stage of the disease. Irregular thickening of the common bile duct wall and biliary dilation are the findings visualised by abdominal CT and US that are suspicious for fascioliasis [8,9]. Adult flukes promote hyperplasia and hypertrophy of the duct epithelium, resulting in thickening of the duct walls and periductal fibrosis . In chronic fasciolasis, abdominal US results may be either normal or may show mobile vermiform structures without acoustic shadowing within the gall bladder and in the bile ducts, representing flukes that may be confused with stones [11,12]. CT scans of the abdomen almost always show abnormalities in patients with a suspected diagnosis of fascioliasis. After administration of contrast material, the abnormalities seen most commonly on CT scans are multiple, small, indiscrete, hypodense lesions 2–10 mm in diameter, and microabscesses arranged in a tunnel-like branching pattern, with frequent subcapsular locations of the lesions. In rare instances, abscess-like lesions 7–10 cm in diameter can be seen. Liver capsular thickening and subcapsular haemorrhage can also be detected [11,12]. Magnetic resonance imaging provides similar findings, which are suggestive of various changes associated with traumatic hepatitis caused by the migration of the fluke in the liver . Invasive techniques, such as percutaneous cholangiography and endoscopic retrograde cholangiography, can reveal some abnormalities, but are generally not required for the diagnosis [14,15]. Liver biopsy is not usually indicated, but if it is performed, necrotic debris, track-like destruction of parenchyma, polymorphonuclear infiltration with abundant eosinophils, Charcot–Lyden crystals, granulomas with or without eggs, fibrosis and bile duct proliferation are the classical findings from the biopsy specimens .
Although praziquantel is the drug of choice for other trematodes, this agent is ineffective against F. hepatica. The CDC recommends triclabendazole as the first-line agent for the treatment of F. hepatica infection. Dizziness, headache, fever and abdominal pain 5–6 days after the initiation of treatment are the side-effects encountered most commonly . Bithionol is an alternative drug for the treatment of F. hepatica infection. Cure rates of up to 100% have been reported with three divided doses on alternate days, with the disadvantage of frequent side-effects, including nausea, vomiting, pruritus, urticaria, abdominal colic and rash .
The main difficulty with F. hepatica infection is the delay in arriving at a diagnosis, particularly in Western countries, despite the fact that large outbreaks have been reported from different parts of the world . When a patient presents with abdominal pain and fever, serology for F. hepatica should be obligatory if elevated liver enzymes and eosinophilia accompany hypodense lesions with irregular margins on the CT scan. CT is very helpful in obtaining a clear-cut diagnosis of the disease and in distinguishing fascioliasis from other causes. Although the world is becoming more developed, natural disasters still occur on a regular basis. Contaminated water and water plants are the potential sources of F. hepatica infection. In such circumstances, every effort should be made to exclude the possibility of F. hepatica infection, which is not just an historical problem, but remains a disease of the modern world.