1. F ASCIOLA HEPATICA - T HE L IVER F LUKE Dr. Sanjay Kumar Jha Department of Zoology P.G.G.C.G. - 42, Chandigarh

2. S YSTEMATIC P OSITION Phylum-Platyhelminthes Class-Trematoda Order-Digenea Family-Fasciolidae Genus-Fasciola Species-hepatica

3. N ATURAL H ISTORY  Fasciola hepatica is a parasitic species found in sheep and goats. It was first found in the sheep liver in France and hence commonly known as Sheep liver fluke. A similar species F. gigantica (F. indica) occurs in cattles.  HABITAT: Fasciola hepatica is found all over the world. It is more common in localities with low-lying wet pastures or marshy areas which provides a suitable environment for its intermediate host, a fresh-water snail. The adult worms inhabit the large bile ducts in the liver of sheep and goats. This animal thus have digenetic life cycle, i.e., have two hosts: (a) Primary host (sheep and goats) for adult parasite, and (b) Secondary host (freshwater snail) for its larval stage.  HABITS: It keeps attached to the wall of the bile ducts by suckers. It is incapable of active locomotion, but shows slow movement by muscular contraction; respires anaerobicaly as oxygen is not available in the bile ducts; holozoic in nutrition, feeds on blood, bile, tissue fluid, mucus and epithelial cells and cell fragments of bile ducts; hermaphrodite undergoing self or cross-fertilization; many larval stage with a life span of 5 years.

4. E XTERNAL C HARACTERS  Form, Colour, Size and Symmetry: Adult worm has a soft, flat, dark-brown, leaf-like body with bilateral symmetry, measuring about 25 mm. in length and 12 mm. in breadth (max. at anterior third of the body).  Body Parts: Anterior end has small conical projection called head lobe or cephalic cone bearing mouth on the ventral side surrounded by a circular disc called anterior or oral sucker used for attachment or feeding. Ventral surface also has a larger, cup-shaped sucker (little posterior to head lobe) called ventral sucker or acetabulum used for attachment to the bile duct of host. A small genital pore or gonopore is present between the two suckers. An excretory pore is situated at the hind end. No anus.

5. E XTERNAL C HARACTERS (C ONTD.)  BODY WALL: The body wall of liver fluke consists of three layer: tegument, basal lamina and musculature. A Tegument is a living, nonciliated cytoplasmic syncytium continuous with the cytoplasm of the large cells submerged in the paranchyma. These cells are irregular and lie next to the musculature in a row. The teguments bears microvilli, spinules or spines and contains mitochondria, golgi, ER, secretory granules and vesicles bounded externally by plasma membrane and internally by a basal lamina or basement membrane. Musculature consists of three layers:- (a) Outer layer of circular muscles fibres, (b) Middle layer of longitudinal muscle fibres, (c) Inner layer of oblique muscle fibres.  FUNCTIONS: It maintains the body form, protects the delicate internal organs, spinules provide attachment to the bile ducts, nitrogenous wastes diffusion, absorbs glucose and some amino acids in gut flukes, provides site for gaseous exchange and to perform movements.  PARENCHYMA: is a special spongy, mesodermal tissue that fills the spaces around the internal organs, hence there is no coelom in Fasciola hepatica. It consists of large irregular mesenchyme cells, the branching process from which forms a network with fluid-filled spaces (matrix) in between. The parenchyma contains some free cells which give rise to lymphocytes and gonads and also contributes towards tegument.

6. D IGESTIVE S YSTEM  MORPHOLOGY: Alimentary canal is complete having mouth, buccal cavity, pharynx, oesophagus, intestine and anus. The intestine consists of two main limbs or crura, the left and the right, giving off both externally and internally, side branches all along its course, called intestinal caeca. The inner caeca is short and simple while the outer caeca are longer and subdivided.  HISTOLOGY: Wall of intestine consists of columnar epithelium surrounded by a feeble musculature of circular and longitudinal muscle fibres. The caecal epithelium is glandular and absorptive. The rest of alimentary canal have cuticular lining.  PHYSIOLOGY: Nutrition involves several processes namely ingestion, digestion, absorption, assimilation and egestion. Food is bile, mucus, epithelial cells eroded by spinules and blood and tissue fluid oozing from injuries of the host.

7. N ERVOUS S YSTEM The nervous system of liver fluke is amazingly well developed despite the parasitic and sluggish mode of life. It consists of two parts, viz., C.N.S. and P.N.S.. (1) Central Nervous System: comprises of a nerve ring and three pairs of nerve cords. The nerve ring surrounds the oesophagus and bears three ganglia. Two of these are lateral in position and called cerebral ganglia while the third one is median and on the lower side called the ventral ganglion. The nerve cords arise from the cerebral ganglia and extend backward. There are dorsal, ventral and lateral nerve cords out of which the lateral cords are best developed and alone reach the hind end of the body. They are interconnected at intervals by transverse nerves, the commissures. (2) Peripheral Nervous System: It comprises of nerves that extends between the C.N.S. and various parts of body. (3) Sense Organs: no special sense organs but have simple bulb like endings of tactile or tangoreceptors.

8. E XCRETORY S YSTEM The excretory system of Fasciola includes flame cells (protonephridia) and excretory passageways. i. Flame Cells: they are characteristic of flatworms. They are numerous and scattered throughtout the parenchyma. A flame cell gives off from its surface a number of branched cytoplasmic processes that penetrates between the parenchyma cells, contains nucleus on one side and enclosed a large cavity. A bundle of long, vibratile cilia projects into the cavity of the cell form one side which perform regular, undulating movements that look like the flickering candle flame, hence, the name given. ii. Excretory Passageways: The cavities of the flame cells leads to fine excretory capillaries that open into larger excretory tubules, which in turn opens into still larger excretory tubes. 4 excretory tubes (2 dorsal and 2 ventral) are formed in this manner in anterior part of body which leads into a large median duct, the longitudinal excretory canal or bladder which opens out by excretory pore. All have simple cuboidal ciliated epithelium except the bladder (nonciliated wall). Functions: Ultrafilteration and Reabsorption.

9. R EPRODUCTIVE S YSTEM Fasciola is hermaphrodite. Its reproductive system shows maximum development. It has elaborate male and female organs. A. Male Reproductive System: includes Testes (two in number, highly branched tubule, occurred in tandem in the centre of the body); Vasa deferentia; Seminal vesicle or Vesicula seminalis; Prostatic duct or Pars prostatica; Penis or Cirrus and Genital atrium. B. Female Reproductive System: comprises of an Ovary (single, less branched tube like testis but much smaller);.an Oviduct; Vitelline glands and their ducts; Uterus; Genital atrium; Laurer’s canal and Mehlis’s gland. FERTILIZATION:- Both cross- (more common) and self fertilization occurs in liver flukes. Capsule formation takes place in the terminal part of the oviduct having a operculum or lid on one side. One worm can produces 500,000 capsules. A sheep can have 200 adult flukes in its bile duct and can have 100 million capsules in one host.

10. L IFE H ISTORY Development in Fasciola zygote starts before the capsules are released from the uterus. There are five larval stages in the life history of Fasciola. They are: (a) Miracidium (free living, conical, ciliated larva which do not feed and swims on the surface water film in search of intermediate host which is a freshwater snail, Limnaea or Planorbis sp. otherwise dies in 24 hrs. (b) Sporocyst (oval, sac-like larva without cilia, eye spots, brain and penetration glands inside the host) (c) Redia (1 sporocyst can produce 8 redia larva; is elongated, cylindrical in shape having small anterior mouth which leads to suctorial pharynx and small intestine; characteristic collar and lappets on anterior and posterior sides respectively). (d) Cercaria (small, flat, heart-shaped, 0.5 mm tailed larva which migrates from digestive gland to pulmonary sac and finally leaves the snail through its pulmonary aperture). One Miracidium can produces upto 3200 Cercaria in a snail in about 5-6 weeks. (f) Metacercaria (encysted form of cercaria, waits for being swallowed by a new host along with vegetation).

11. R ISK O F D EATH Fasciola faces risk of destruction in every stage of its life history. 1) Development of the embryo in a capsule that has passed out of the host continues only if suitable temperature, pH and moisture are available in the environment. 2) Miracidium after escaping from the capsule may not find a suitable host within 24 hrs. and die. 3) The snail that harbours miracidia may be destroyed. 4) The cercaria which leave the snail may be ingested by animals other than the primary hosts of Fasciola. 5) The encysted metacercaria may die of dessiccation of not taken up by a proper host within a reasonable period. EXCESSIVE MULTIPLICATION COMPENSATES FOR THE ABOVE RISKS.

12. N ATURE O F L IFE H ISTORY HETEROGAMY: The life history of Fasciola involves alteration of sexual generation represented by the adult worm with the parthenogenetic generations represented by Redia and Cercaria produced from propagatory or germ cells of the zygote. Such an alternation of generations is known as Heterogamy. (It may be recalled that in Obelia, there is alternation of generation of sexual and asexual generations (metagenesis). POLYEMBRYONY: The germ cells present in the larval forms are not parthenogenetic eggs but are diploid cells produced by mitotic divisions of propagatory cells separated from the zygote after first cleavage. Thus the several types of larvae produced form single zygote sets up a phenomenon called Polyembryony and more appropriate delayed polyembryony because all the larvae are not produced at one time but at separate intervals. PATHOGENICITY: damages cells of liver and interferes with the digestion of food by blocking the bile ducts, heavy infection causes ‘Fascioliasis or Liver-rot’ resulting in complete breakdown of liver. Its excretory matter is also poisonous.

13. C ONTORL M EASURES  Destruction of Snails (their intermediate host necessary for the development of Miracidium larva) is the most suitable measure of controling the parasite.  Draining the wet pastures which is suitable habitat for snails.  Introducing Ducks and Geese in wet ponds will eat up the snails and removes intermediate hosts of Fasciola.  Application of Lime on pastures increases the pH of water making it more alkaline (pH>7.8) which is not suitable for hatching of the capsules of Fasciola hepatica.  Adult worms in the host can be killed with Antihelminthic drugs.