Fasciola hepatica: The Common Liver Fluke

Fasciola hepatica is a parasitic flatworm that infects the livers of various mammals, including humans. It is also known as the common liver fluke or the sheep liver fluke, and it causes a disease called fasciolosis or fascioliasis. In this article, we will explore the morphology of Fasciola hepatica, how it differs from other liver flukes, and how it can be identified.

What is Fasciola hepatica?

Fasciola hepatica is a member of the class Trematoda, phylum Platyhelminthes. It belongs to the family Fasciolidae, which includes another species of liver fluke, Fasciola gigantica. These two species are closely related and can mate with each other, producing hybrid forms that have intermediate characteristics.

Fasciola hepatica is distributed worldwide, especially in regions where sheep or cattle are raised. It can infect a wide range of definitive hosts, such as ruminants, equids, lagomorphs, rodents, and humans. The infection occurs when the host ingests the metacercariae (the infective stage) of the parasite, which are encysted on aquatic plants or other substrates. The metacercariae then excyst in the duodenum and penetrate the intestinal wall, reaching the peritoneal cavity. From there, they migrate through the liver parenchyma into the bile ducts, where they mature into adult flukes and produce eggs. The eggs are passed in the feces and hatch in freshwater, releasing miracidia (the larval stage) that infect snails of the family Lymnaeidae (the intermediate hosts). In the snails, the parasites undergo several developmental stages (sporocysts, rediae, and cercariae) before emerging as metacercariae and completing the life cycle.

What does Fasciola hepatica look like?

Fasciola hepatica has a flat and leaf-like body shape, with a characteristic taper at both ends. The anterior end has an oral sucker that helps the parasite attach to the host’s tissue, and a ventral sucker that is used for locomotion and feeding. The posterior end is larger and contains most of the reproductive organs.

The adult worms of Fasciola hepatica measure up to 10 mm in length and 2.5 mm in width. They are brownish in color and have a smooth surface. They have a simple digestive system that consists of a mouth, a pharynx, an esophagus, and a branched intestine that extends throughout the body. They also have a complex reproductive system that includes lobed testes (located in the anterior part of the body), an ovary (located behind the testes), a uterus (that coils around the intestine), and a genital pore (that opens near the ventral sucker). Fasciola hepatica is hermaphroditic, meaning that it has both male and female reproductive organs in the same individual. However, it usually reproduces by cross-fertilization with another worm of the same species.

How does Fasciola hepatica differ from other liver flukes?

Fasciola hepatica is similar to another liver fluke, Clonorchis sinensis, which is also known as the Chinese liver fluke or the oriental liver fluke. Both parasites have a flat and leaf-like body shape, an oral sucker and a ventral sucker, and infect the bile ducts of their hosts. However, there are some differences between them that can be used to distinguish them morphologically.

One of the main differences is the size and shape of their eggs. Fasciola hepatica eggs are broadly ellipsoidal, operculated (having a lid-like structure), and measure 130–۱۵۰ μm by 60–۹۰ µm. Clonorchis sinensis eggs are smaller (27–۳۵ μm by 11–۲۰ µm), more oval-shaped, and have a prominent knob at one end.

Another difference is the location and shape of their reproductive organs. Fasciola hepatica has lobed testes that are located in the anterior part of the body, just behind the ventral sucker. The ovary is also in the anterior region, behind the testes. Clonorchis sinensis has oval testes that are located in the posterior part of the body, near the end of the intestine.

The ovary is also in the posterior region, between the testes.

How can Fasciola hepatica be identified?

Fasciola hepatica can be identified by examining its morphology under a microscope or by using molecular techniques such as PCR (polymerase chain reaction) or DNA sequencing. The morphology of the adult worms, the eggs, and the larval stages can be used to diagnose the infection and differentiate it from other liver flukes. The molecular techniques can be used to confirm the identification and to detect hybrid forms or genetic variations of the parasite.

Conclusion

Fasciola hepatica is a parasitic flatworm that infects the livers of various mammals, including humans. It has a flat and leaf-like body shape, with a characteristic taper at both ends. It has an oral sucker and a ventral sucker, and lobed testes and an ovary in the anterior part of the body. It produces broadly ellipsoidal and operculated eggs that hatch in freshwater and infect snails of the family Lymnaeidae. It can be identified by its morphology or by molecular techniques.