Life History of Fasciola hepatica
Fasciola is digenetic, i.e., the life cycle is completed in two alternating hosts. One is the
primary or definitive host in which the adult lives, the sheep or cow and the other is the
secondary or intermediate host in which numerous larval stages passed the fresh water
snail of genus Lymnaea, Planorbis, etc. This kind of life cycle, involving two different types
of hosts, is termed as digenetic.
(i) Copulation and Fertilization:
Though F. hepatica is hermaphrodite even then cross- fertilisation is of common
occurrence. Hence, before fertilisation, copulation occurs. During copulation, which occurs
in the bile duct of the sheep, the Cirrus of one Fasciola is inserted into the Laurer’s canal of
other Fasciola and the spermatozoa are deposited into the oviduct, so that cross-
fertilisation takes place.
During self- fertilisation, the sperms from the same Fasciola enter the female genital
aperture and pass down the uterus to fertilize the eggs in the oviduct.
(ii) Formation of Capsules:
The eggs are brownish in colour, oval in shape and measure about 130 to 150 μ in length
and 60 to 90 μ in wide.
As referred, the eggs are fertilised in the oviduct, the fertilised eggs receive yolk cells from
vitelline glands and they get enclosed in a chitinous shell formed by granules in the yolk
cells giving out droplets, the shell hardens and becomes brownish yellow; the shell has an
operculum or lid. The complete ‘eggs’ are called capsules which are large in size and they
pass into the uterus where development starts. Capsules come out of the gonopore into
the bile duct of the sheep, they reach the intestine and are passed out with the faeces.
(iii) Development of Fasciola hepatica:
Development starts in the uterus and is continued on the ground. The fertilised egg divides
into a small propagatory cell and a larger somatic cell due to unequal and holoblastic
cleavage. The somatic cell divides and forms the ectoderm of the larva. Later the
propagatory cell divides into two daughter cells. One of which forms the endoderm and
mesoderm of the larva, and the other forms a mass of smaller germ cells at the posterior
end of the larva.
, (iv) Miracidium Larva:
In two weeks time, a small ciliated miracidium larva is formed and it comes out of the shell
by forcing the operculum. It is the first larval stage involved in the life cycle. The miracidium
produces a proteolytic enzyme which erodes the lower surface of the operculum.
Miracidium larva is a minute (~0.07mm), oval and elongated, free-swimming stage which is
covered with 18 to 21 flat ciliated epidermal cells arranged in five rows.
The miracidium does not feed, It swims about in water or moisture film, but it dies within 8
to 24 hours unless it can reach a suitable intermediate host, the snails of genus Lymnaea or
Bulinus or Planorbis or Succinea, etc.
After getting a suitable host the miracidium adheres to it by its apical papilla and enters the
pulmonary sac of the snail, from where it penetrates into the body tissues with the aid of
penetration glands and finally reaches to snail’s digestive gland. In the tissues the
miracidium casts off its ciliated epidermis, loses its sense organs and it swells up and
changes in shape to form the second larval stage, the sporocyst larva.
Fasciola is digenetic, i.e., the life cycle is completed in two alternating hosts. One is the
primary or definitive host in which the adult lives, the sheep or cow and the other is the
secondary or intermediate host in which numerous larval stages passed the fresh water
snail of genus Lymnaea, Planorbis, etc. This kind of life cycle, involving two different types
of hosts, is termed as digenetic.
(i) Copulation and Fertilization:
Though F. hepatica is hermaphrodite even then cross- fertilisation is of common
occurrence. Hence, before fertilisation, copulation occurs. During copulation, which occurs
in the bile duct of the sheep, the Cirrus of one Fasciola is inserted into the Laurer’s canal of
other Fasciola and the spermatozoa are deposited into the oviduct, so that cross-
fertilisation takes place.
During self- fertilisation, the sperms from the same Fasciola enter the female genital
aperture and pass down the uterus to fertilize the eggs in the oviduct.
(ii) Formation of Capsules:
The eggs are brownish in colour, oval in shape and measure about 130 to 150 μ in length
and 60 to 90 μ in wide.
As referred, the eggs are fertilised in the oviduct, the fertilised eggs receive yolk cells from
vitelline glands and they get enclosed in a chitinous shell formed by granules in the yolk
cells giving out droplets, the shell hardens and becomes brownish yellow; the shell has an
operculum or lid. The complete ‘eggs’ are called capsules which are large in size and they
pass into the uterus where development starts. Capsules come out of the gonopore into
the bile duct of the sheep, they reach the intestine and are passed out with the faeces.
(iii) Development of Fasciola hepatica:
Development starts in the uterus and is continued on the ground. The fertilised egg divides
into a small propagatory cell and a larger somatic cell due to unequal and holoblastic
cleavage. The somatic cell divides and forms the ectoderm of the larva. Later the
propagatory cell divides into two daughter cells. One of which forms the endoderm and
mesoderm of the larva, and the other forms a mass of smaller germ cells at the posterior
end of the larva.
, (iv) Miracidium Larva:
In two weeks time, a small ciliated miracidium larva is formed and it comes out of the shell
by forcing the operculum. It is the first larval stage involved in the life cycle. The miracidium
produces a proteolytic enzyme which erodes the lower surface of the operculum.
Miracidium larva is a minute (~0.07mm), oval and elongated, free-swimming stage which is
covered with 18 to 21 flat ciliated epidermal cells arranged in five rows.
The miracidium does not feed, It swims about in water or moisture film, but it dies within 8
to 24 hours unless it can reach a suitable intermediate host, the snails of genus Lymnaea or
Bulinus or Planorbis or Succinea, etc.
After getting a suitable host the miracidium adheres to it by its apical papilla and enters the
pulmonary sac of the snail, from where it penetrates into the body tissues with the aid of
penetration glands and finally reaches to snail’s digestive gland. In the tissues the
miracidium casts off its ciliated epidermis, loses its sense organs and it swells up and
changes in shape to form the second larval stage, the sporocyst larva.
