Fasciola, commonly known as the liver fluke, is a genus of parasitic trematodes. There are three species within the genus Fasciola: Fasciola nyanzae, Fasciola hepatica and Fasciola gigantica. Fasciola hepatica and F. gigantica are known to form hybrids. Both F. hepatica and F. gigantica and their hybrids infect the liver tissue of a wide variety of mammals, including humans, in a condition known as fascioliasis. F. hepatica measures up to 30 mm by 15 mm, while F. gigantica measures up to 75 mm by 15 mm. Fasciola nyanzae is thought to exclusively infect the common hippopotamus, Hippopotamus amphibius.thumb|Life Cycle of Fasciola
Species
- Fasciola nyanzae <small>Leiper, 1910</small>
- Fasciola hepatica <small>Linnaeus, 1758</small>
- Hybrid or introgressed populations of Fasciola gigantica × Fasciola hepatica
Life cycle
Fasciola pass through five phases in their life cycle: egg, miracidium, cercaria, metacercaria, and adult fluke. The cercariae then develop into metacercarial cysts. When these cysts are ingested along with the aquatic plants by a mammalian host, they mature into adult flukes and migrate to the bile ducts.
Animal hosts
The intermediate hosts, where Fasciola reproduce asexually, are gastropods from the family Lymnaeidae, also known as pond snails.
A wide variety of mammals can be definitive hosts, where Fasciola reach adulthood and reproduce, including pigs, rodents, ruminants, and humans. The most important animal reservoir hosts for human infections are sheep and cattle.
Geographic distribution
thumb|Range of F. hepatica
Fasciola are widespread and inhabit 70 countries and parts of all continents except for Antarctica. It is most common in areas with sheep and cattle are raised.
History and discovery
Evidence of fascioliasis in humans exists dating back to Egyptian mummies that have been found with Fasciola eggs. Cercariae of F. hepatica in a snail and flukes infecting sheep were first observed in 1379 by Jehan De Brie. The life cycle and hatching of an egg were first described in 1803 by Zeder.
Prevention and treatment
Fascioliasis is treated with triclabendazole. There is no vaccine for Fasciola currently available. This is of particular concern in areas where animal waste is used as fertilizer for the cultivation of watercress, as the full life cycle of Fasciola can sustained while contaminating crops intended for human consumption. Another method is treating entire communities that are at risk for contracting fascioliasis with triclabendazole.