Fascioliasis is a parasitic disease affecting the liver and bile ducts in humans and other mammals. It is caused by flatworms, known as liver flukes. This infection can lead to various health issues. The disease has a global presence, particularly in regions with livestock farming and specific agricultural practices.
The Parasite’s Journey and Human Infection
Fascioliasis is caused by two species of parasitic flatworms: Fasciola hepatica and, less frequently, Fasciola gigantica. These parasites have a complex life cycle involving aquatic snails and vegetation. Their eggs are released into freshwater environments through the feces of infected animals.
Once in freshwater, these eggs hatch into miracidia, a larval stage which infects specific freshwater snails, typically from the Lymnaeidae family. Inside the snail, the miracidia develop into sporocysts, then rediae, and finally into cercariae. These cercariae are released from the snail and swim in the water.
The free-swimming cercariae then attach to aquatic plants, such as watercress, or other vegetation, where they encyst, forming metacercariae. These metacercariae are the infective stage for humans and other mammals. Infection occurs when individuals consume raw or undercooked aquatic plants contaminated with these cysts or drink water containing them.
Upon ingestion, the metacercariae excyst in the small intestine, releasing immature flukes. These flukes penetrate the intestinal wall and migrate through the abdominal cavity to the liver. They burrow through the liver tissue before settling in the bile ducts, where they mature into adult flukes and begin to lay eggs.
Recognizing Symptoms and Confirming Diagnosis
Fascioliasis symptoms often present in two distinct phases: an acute (migratory) phase and a chronic (biliary) phase. The acute phase occurs as the immature flukes migrate through the liver tissue. Symptoms during this stage include fever, abdominal pain, an enlarged and tender liver (hepatomegaly), nausea, vomiting, and sometimes skin rashes like urticaria.
This acute phase can last from days to several months, with an incubation period of up to three months before symptoms appear. As the flukes mature and settle in the bile ducts, the infection progresses to the chronic phase. This stage may be asymptomatic in some individuals, but it can also lead to intermittent abdominal pain, inflammation of the bile ducts (cholangitis), gallstones (cholelithiasis), and jaundice.
Diagnosing fascioliasis involves a combination of clinical evaluation, laboratory tests, and imaging studies. Stool examination can detect Fasciola eggs, particularly in the chronic phase, although eggs may not always be present, especially in early infections or due to intermittent shedding. Serological tests, such as ELISA and Western blot, detect antibodies against the parasite in the blood, indicating an active or past infection.
Imaging techniques visualize abnormalities in the liver and bile ducts. Ultrasound, Computed Tomography (CT) scans, and Magnetic Resonance Imaging (MRI) can reveal lesions in the liver parenchyma during the acute phase or show thickening and obstruction of the bile ducts in the chronic stage. An elevated count of eosinophils in blood tests (eosinophilia) often suggests a parasitic worm infection.
Treatment and Prevention Strategies
The primary medication used to treat fascioliasis is triclabendazole, an anthelmintic drug effective against both immature and adult liver flukes. It works by disrupting the parasite’s tegument (outer covering) and interfering with its protein synthesis. The World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) recommend triclabendazole as the drug of choice for human fascioliasis.
Treatment typically involves one or two oral doses of 10 mg/kg, given 12 to 24 hours apart, and taken with food. This medication has shown high efficacy in clearing the infection across various forms and stages. While resistance to triclabendazole has been reported in livestock, no confirmed human resistance has been reported to date.
Preventing fascioliasis focuses on avoiding contaminated food and water. A key strategy is to thoroughly cook all aquatic vegetables, particularly watercress, before consumption, especially if sourced from areas where the parasite is known to be endemic. Avoiding raw aquatic plants altogether is also advisable.
Ensuring drinking water safety is another important preventive measure. Public health initiatives in endemic regions often include controlling snail populations, intermediate hosts, by chemically treating water sources. Limiting livestock access to aquatic plants and separating human living areas from animal husbandry can reduce parasite spread.