Fasciola infection, also known as fascioliasis, is a parasitic disease caused by flatworms called liver flukes. These parasites, primarily Fasciola hepatica and Fasciola gigantica, infect the liver and bile ducts of various mammals, including sheep, cattle, and humans. It is a global plant-borne trematode zoonosis, impacting animal and human health. While more prevalent in livestock, human infections occur in over 70 countries across all continents except Antarctica.
How Fasciola Spreads
Fasciola’s life cycle involves definitive mammalian hosts and an intermediate snail host. Adult flukes in infected animals, like sheep and cattle, release eggs through feces. In fresh water, eggs hatch into microscopic miracidia, which infect specific freshwater snails.
Inside the snail, miracidia undergo developmental stages, multiplying and emerging as free-swimming cercariae. Cercariae detach from the snail and encyst on aquatic plants, like watercress, forming the infective stage known as metacercariae. Humans become infected by consuming contaminated raw aquatic vegetables or water containing metacercariae. Animal hosts act as reservoirs, contributing to environmental contamination that can lead to human infection.
Recognizing and Addressing Human Infection
Human fascioliasis presents with symptoms varying by infection stage. The acute, or invasive, phase occurs when immature flukes migrate through the intestinal wall and liver tissue, lasting up to three to four months after exposure. During this period, individuals may experience fever, malaise, abdominal pain (especially in the upper right quadrant), skin rashes, and an enlarged liver. The migration of the parasites through the liver can cause tissue damage and inflammation.
As the flukes mature and settle in the bile ducts, the infection enters the chronic phase, which can be asymptomatic for months or years. Symptoms include intermittent abdominal pain, jaundice (yellowing of the skin), and anemia, due to inflammation or obstruction of the bile ducts. Diagnosis involves several methods, as finding eggs in stool samples can be challenging, particularly in early infections or those with a low parasite burden. Blood tests that detect antibodies specific to Fasciola are used, becoming positive within two to four weeks post-infection. Imaging techniques like ultrasound or CT scans can reveal liver lesions or bile duct abnormalities caused by the migrating or adult flukes.
Triclabendazole is the treatment for human fascioliasis. This medication is effective against both immature and adult flukes and is administered orally, often with food to enhance absorption. The U.S. Food and Drug Administration (FDA) approved triclabendazole for patients aged six years and older in 2019. While well-tolerated, some reports of resistance have emerged, particularly in animal infections.
Preventing Fasciola Infection
Preventing Fasciola infection involves avoiding contaminated food and water. Thoroughly cooking aquatic vegetables, especially those from areas where Fasciola is common, is a step, as heat kills the infective metacercariae. Raw watercress and other freshwater plants should be avoided, particularly if their source is unknown or if they come from grazing areas. Drinking safe, treated water is also a preventive measure, as contamination can occur through water or vegetables washed or irrigated with contaminated water. Practicing good hygiene, including proper handwashing, reduces the risk of exposure.
Public health efforts contribute to prevention strategies. These include surveillance and control programs for animal infections, particularly in livestock such as sheep and cattle, which serve as reservoirs for the parasite. Managing snail populations, the intermediate hosts, through environmental control measures disrupt the parasite’s life cycle. Educational initiatives that raise awareness about safe food preparation and the risks associated with consuming uncooked aquatic plants are valuable in preventing human fascioliasis.