Fasciola hepatica (L., fasciola = small bandage; Gr., hepar = liver), the sheep liver fluke, lives as an endoparasite in the bile passages of sheep.
Liver flukes are typical digenean trematodes and are commonly called “flatworms” or “flukes” on account of their flat, leaf-like structure. Fasciola hepatica is the common liver fluke of sheep. It is the first trematode whose life history was described by Thomas in 1883. It is of much importance as it causes fascioliasis—a disease that causes damage to liver- tissues and bile ducts of sheep.
Etymology
Latin: fasciola, small bandage
The species name hepatica stems from the Greek word hepar meaning liver.
Its life cycle is digenetic, i.e., completed in two hosts (a primary vertebrate host, the sheep and a secondary or intermediate invertebrate host, the gastropod mollusc). The adult parasite is found in the primary host, while a part of its life cycle as larval stages are found in the invertebrate host.
Fasciola hepatica, in addition to sheep, also infects other vertebrates like goat, deer, horse, dog, ass, ox and occasionally man. Its secondary hosts are either Planorbis sps, Bulinus sps., or Limnaea truncatula, all being freshwater gastropod molluscs.
Fasciola hepatica is worldwide in distribution, particularly sheep and cattle raising areas are the primary zones where human beings are also infected. Its other Indian species, F. gigantica (= indica) is found in the bile passages of buffaloes, cow, goats and pigs.
Structure of Fasciola Hepatica
Shape, Size and Colour
F. hepatica has a thin, dorsoventrally flattened, leaf-shaped, elongated and oval body. It measures about 25 to 30 mm in length and 4 to 12 mm in breadth.
The maximum width is at about anterior third of the body from where the body tapers anteriorly as well as posteriorly, however, the anterior end is somewhat rounded, while it is bluntly pointed posteriorly. F. indica has its greatest width at about the middle of the body, and the posterior end is rounded.
It is usually pinkish in colour but it appears brownish due to ingested bile of the host.
External Morphology
The anterior end of the body is distinguished into a triangular oral cone or head lobe giving it a shouldered appearance. The head lobe, at its tip, bears a somewhat triangular aperture called mouth.
There are two muscular suckers an oral sucker at the anterior end encircling the mouth, and a large ventral sucker or acetabulum situated midventrally about 3 to 4 mm behind the oral sucker.
The suckers are cup-like muscular organs meant for attachment to the host by vacuum. In addition to mouth aperture, there are two permanent apertures on the body; one situated mid-ventrally in front of the ventral sucker is the common genital aperture or gonopore, and the other is situated at the posterior end of the body called the excretory pore.
In addition to these apertures, a temporary opening of Laurer’s canal appears during the breeding season on the dorsal surface just anterior to the middle of the body. Anus is wanting because alimentary canal is incomplete.