Laboratory Studies
CBC count
Leukocytosis may occur. In developed countries, finding of eosinophilia and history of ingestion of watercress or freshwater plants in a symptomatic individual can be a good guide for further testing for fascioliasis. Eosinophilia is not specific for fascioliasis, as it can occur in many other parasitic infections, especially in endemic areas. Cases without eosinophilia have been reported both in acute and biliary phase. [5]
Eosinophilia may wax and wane during the chronic stage of infection. Among Egyptian children with acute fascioliasis, 14-82% had peripheral eosinophilia. [21]
Erythrocyte sedimentation rate
About one half of affected patients have an elevated erythrocyte sedimentation rate.
Immunoglobulin levels
These may be elevated, particularly immunoglobulins G and E.
Liver function tests
Elevated levels of gamma-glutamyl transpeptidase, alkaline phosphatase, and bilirubin may suggest cholestatic liver injury.
Although rare, elevated transaminase levels suggest hepatocellular injury.
Stool examination for ova and parasites
Detection of fasciolid eggs in the stools of the infected patients is the most definitive test for diagnosis. This test has some limitations as it can be falsely negative in the acute phase of disease and has low sensitivity in the later phases as well. [18] The small number of eggs in stool requires multiple specimens. The eggs measure 130-150 X 60-90 μm and can be confused with Fasciolopsis buski eggs. The FLOTAC technique may have superior sensitivity to standard sedimentation stool examinations. [22]
ELISA for Fasciola coproantigens may be performed on stool specimens. [23]
Flukes that measure 30 X 15 mm almost never appear in stool; the rare exceptions follow successful treatment.
Fasciola hepatica egg in an unstained wet mount (400x magnification). F hepatica eggs are broadly ellipsoidal, operculated, and measure 130-150 μm by 60-90 μm. Courtesy of the CDC's DPDx, Division of Parasitic Diseases and Malaria.
Antibody detection
Antibody detection are useful during the acute phase of infection as the acute manifestations of human fascioliasis may precede the appearance of eggs in the stool by several weeks. Immunodiagnostic tests may be useful for confirmation of chronic fascioliasis when egg production is low or sporadic.
Immunodiagnostic tests for human Fasciola hepatica infection are: [24] enzyme immunoassays (EIA) with excretory-secretory (ES) antigens combined with confirmation of positive test by immunoblot. Specific antibodies to Fasciola may be detectable 2 to 4 weeks after infection (5 to 7 weeks before eggs appear in stool). Sensitivity for the FAST-ELISA format of EIA was 95%, sensitivity for immunoblot using 12-, 17-, and 63-kDa antigens appeared to be 100%. Antibody levels decrease to normal 6 to 12 months after treatment and can be used to predict the success of therapy.
Polymerase chain reaction (PCR) assays
PCR assays have been developed for the rapid diagnosis of fascioliasis. [25, 26]
Imaging Studies
Chest radiography
In patients with pulmonary symptoms, parenchymal infiltrates are rarely visible. A right-sided pleural effusion is also rare.
Ultrasonography
Ultrasonography may reveal hypodense/hypoechoic lesions in the liver that correspond to the burrow tracks of the larvae. Ultrasonography may reveal the adult fluke in a bile duct or the gallbladder. Ultrasonography rarely reveals scant ascites.
CT scanning
CT scanning may reveal multiple lesions that measure 1-10 mm or tunnels in the liver parenchyma. [27, 28] A radiating pattern of tunnels is diagnostic. CT scanning may also reveal an adult fluke in a bile duct or the gallbladder.
Findings of the ultrasound and CT scan can sometimes be confused with alternate diagnosis such as malignancy and stones. [5]
MRI
MRI may suggest granulomata of the liver parenchyma and may provide findings similar to CT scanning.
Cholangiography
ERCP is considered the gold standard technique of imaging of the biliary tract in patients with chronic phase of infection. It also aids in management of the fascioliasis with ERCP guided sphincterotomy and removal of adult flukes in chronic cases with obstructions of bile duct. [5]
Adult of F hepatica observed with ERCP imaging in the common bile duct of a human patient. Courtesy of the CDC's DPDx, Division of Parasitic Diseases and Malaria (Dr. Subhash Agal, Kokilaben Dhirubhai Ambani Hospital, Mumbai, India).
US-guided gallbladder aspiration
This can reveal eggs in the bile, even when stool examination test results are negative.
Technetium-99 scanning
This imaging study reveals multiple intrahepatic defects in approximately 50% of cases.
Other Tests
Bone marrow aspiration, performed only as part of the diagnostic evaluation for other conditions, can reveal increased bone marrow eosinophils.
Procedures
Duodenal aspiration may reveal eggs.
Liver biopsy findings include the following:
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Liver biopsy can reveal microabscesses and tunnels of parenchymal necrosis, surrounded by inflammatory infiltrates containing abundant eosinophils.
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Older lesions may be fibrotic.
Laparoscopy often reveals multiple gray-white and yellow nodules, 2-20 mm in diameter, and short vermiform cords on the liver surface. Rarely, these nodules may occur throughout the peritoneal cavity and intestine wall.
Exploratory laparotomy may reveal identical findings as laparoscopy; flukes are often present in the bile duct or gallbladder.
Upper GI endoscopy is associated with the following:
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Endoscopy can reveal a filling defect in the bile duct.
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Endoscopic removal of the fluke is possible.
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Administration of intravenous cholecystokinin can promote egg release, which can be sampled endoscopically for diagnosis.
Thoracentesis for pleural effusion may reveal increased eosinophils in pleural fluid.
Histologic Findings
Flukes can be found during autopsy or in surgical specimens. Multiple subcapsular cavities (5-10 mm in diameter) may be present, filled with necrotic material from which necrotic tracks radiate and surrounded by inflammatory infiltrates that contain large numbers of eosinophils.
Fibrosis may characterize older lesions. Tissues taken from ectopic sites of larval migration may demonstrate granulomatous nodules or small abscesses.
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Life cycle of Fasciola hepatica. Immature Fasciola eggs are discharged in the biliary ducts and in the stool (1). Eggs become embryonated in water (2), eggs release miracidia (3), which invade a suitable snail intermediate host (4), including the genera Galba, Fossaria and Pseudosuccinea. In the snail, the parasites undergo several developmental stages (sporocysts (4a), rediae (4b), and cercariae (4c)). The cercariae are released from the snail (5) and encyst as metacercariae on aquatic vegetation or other surfaces. Mammals acquire the infection by eating vegetation containing metacercariae. Humans can become infected by ingesting metacercariae-containing freshwater plants, especially watercress (6). After ingestion, the metacercariae excyst in the duodenum (7) and migrate through the intestinal wall, the peritoneal cavity, and the liver parenchyma into the biliary ducts, where they develop into adult flukes (8). Courtesy of the CDC's DPDx, Division of Parasitic Diseases and Malaria.
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Adult Fasciola hepatica fluke stained with carmine (30 mm by 13 mm). Courtesy of the CDC's DPDx, Division of Parasitic Diseases and Malaria.
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Fossaria bulamoides, a snail host for F hepatica in the western United States. Courtesy of the CDC's DPDx, Division of Parasitic Diseases and Malaria (Conchology, Inc, Mactan Island, Philippines).
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Fasciola hepatica egg in an unstained wet mount (400x magnification). F hepatica eggs are broadly ellipsoidal, operculated, and measure 130-150 μm by 60-90 μm. Courtesy of the CDC's DPDx, Division of Parasitic Diseases and Malaria.
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Adult of F hepatica observed with ERCP imaging in the common bile duct of a human patient. Courtesy of the CDC's DPDx, Division of Parasitic Diseases and Malaria (Dr. Subhash Agal, Kokilaben Dhirubhai Ambani Hospital, Mumbai, India).
