Here is a term paper on ‘Fasciola Hepatica (Liver Fluke)’. Find paragraphs, long and short term papers on ‘Fasciola Hepatica (Liver Fluke)’ especially written for college and medical students.
Term Paper on Fasciola Hepatica (Liver Fluke)
Term Paper Contents:
- Term Paper on the Habits and Habitat of Fasciola Hepatica
- Term Paper on the Morphology of Fasciola Hepatica
- Term Paper on the Digestive System of Fasciola Hepatica
- Term Paper on the Respiration System of Fasciola Hepatica
- Term Paper on the Excretory System of Fasciola Hepatica
- Term Paper on the Nervous System of Fasciola Hepatica
- Term Paper on the Reproductive System in Fasciola Hepatica
- Term Paper on the Control of Fasciola Hepatica
- Term Paper on the Parasitic Adaptations in Fasciola Hepatica
Term Paper # 1. Habits and Habitat of Fasciola Hepatica:
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Fasciola is a digenetic parasite. They are generally known as ‘flukes’. Out of these, the digenetic trematodes are more significant because they are found as parasites in man and his domesticated animals. Fasciola hepatica, the parasite found in the liver of sheep, is generally studied as typical example of trematodes.
Fasciola hepatica is a digenetic trematode. It is an endoparasite in the bile passages and liver of sheep and cattle and completes part of its life cycle in snail. It enjoys worldwide distribution. Thus, its primary host is sheep and secondary host is a freshwater snail, Limnaea, Planorbis or Bulinus.
Term Paper # 2. Morphology of Fasciola Hepatica:
Shape, Size and Colour:
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The body of Fasciola hepatica is delicate and oval in shape. It is dorso-ventrally flattened due to which it appears like a leaf. The anterior part of its body is comparatively broader than the posterior part which is narrow and ends bluntly. The size of its body is form 18 to 30 mm long and 4 to 15 mm broad.
The widest part of the body is at about 1/3 of the total length of the body from the anterior end. The species found commonly in India is F. gigantica. It is found in cattle, goat, pig etc. The middle part of its body is widest.
The colour of the body of Fasciola, recently taken out from the host, is mostly light pink. The lateral sides of the body appear grey or brown due to the presence of vitelline glands. Its alimentary canal appears brownish due to using bile as a food.
Structure:
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1. Head Lobe or Cephalic Cone:
The broad anterior end of body is produced into a conical projection, the head lobe or oral cone or cephalic cone. It bears mouth at its tip.
2. Suckers:
There are two suckers:
(i) Anterior or oral sucker is cup-shaped and muscular. It surrounds mouth. It muscles radiate from the margin of mouth to the periphery. Oral sucker is a suctorial organ. It helps in ingestion as well as in adhesion.
(ii) Posterior or ventral sucker is saucer-shaped. It lies about 3-4 mm from oral sucker mid-ventrally. It is without an aperture and is also known as acetabulum. It is meant for attachment only.
3. Apertures:
(i) Mouth is terminal, situated on the tip of oral cone and is surrounded by oral sucker.
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(ii) Common genital aperture or gonopore lies mid-ventrally a little in front of acetabulum.
(iii) A single excretory pore is situated mid-ventrally at the posterior end.
(iv) Opening of Laurer’s canal appears temporarily during breeding season, a little anterior to the middle of body on the dorsal side.
Body Wall:
Body wall in Fasciola is characteristic and adapted to parasitic mode of life. It is non-ciliated, lacks a cellular epidermis. A tough resistant cuticle covers the fluke and protects it from the juices of the host. It bears small spines or spinules and is non chitinous, being mode of proteins.
The spinules anchor the fluke to the bile duct of the host. The cuticle of F. indica has broad, stout and blunt scales. The epidermis has been lost during development of the cercaria stage.
The body wall of Fasciola consists of the following layers:
1. Tegument,
2. Basement membrane,
3. Musculature and
4. Mesenchyme.
1. Tegument:
It is the outermost covering of body-wall. It is thick, non-ciliated, cytoplasmic syncytium. It contains mitochondria, endoplasmic reticulum, vacuoles, pinocytic vesicles and pore canals. It is secreted by the secretion of tegument secreting cells lying in the mesenchyme and is continuous with their cytoplasmic process.
Before the advent of electron microscope, when body-wall was observed with light microscope, the tegument was described as a non-living homogenous cuticle. Electron microscopic studies have revealed that it is a modified epidermis and is named tegument. The cuticle secreting mesenchyme cells are now called tegument-secreting cells.
2. Basement Membrane:
It is thin membranous layer which is actually at part of the cuticle. It separates the cuticle from the muscle layers.
3. Sub Cuticular Muscle Layer:
It consists of three layers – (i) Circular muscles (ii) Longitudinal muscles (iii) Diagonal muscles.
4. Mesenchyme or Parenchyma:
The space between the muscle layer and body organs is filled with large, irregular branching and fluid-filled uni-or binucleate parenchyma cells. The mesenchyme tissue is derived from mesoderm and serves as packing material. Some mesenchyme cells are large and their processes extend to the base of tegument.
Electron Microscopic studies by Threadgold (1968) have revealed that the so called cuticle of Fasciola is actively a thick layer of multinucleated protoplasm containing mitochondria, canals of endoplasmic reticulum vacuoles and vesicles. It is termed as tegument. It is continuous with tegument secreting cells lying embedded in the mesenchyme.
The outer surface of tegument is thrown into numerous folds. These increase the surface area considerably for the absorption of fluids of the hosts. Further, tegument is perforated by fine pore canals. Through these canals are absorbed into the mesenchyme.
Functions:
(i) Tegument is thick, tough and is not affected by the action of host’s digestive juices. A number of backwardly directed spines anchor the fluke to the wall of bile passages these render protection and help in locomotion. The numerous microvilli present on the outer surface of tegument help in the absorption of some amino acids from host’s tissues and fluids.
(ii) Mesenchyme tissue serves as packing material as an important transport medium and provides support to body of gas.
Term Paper # 3. Digestive System of Fasciola Hepatica:
The digestive system of Fasciola is complicated, much branched and incomplete, as the anus is absent.
It is divisible into the following parts:
1. Mouth and Oral Chamber:
The mouth is a very minute aperture which is situated at the distal free end of the cephalic cone on the ventral surface. It is surrounded by the oral sucker. The Oral Chamber is a funnel-shaped structure which leads into the pharynx.
2. Pharynx:
The pharynx is a small almost circular muscular tube. Many pharyngeal glands present in its thick muscular wall.
3. Oesophagus:
It is a small narrow tube-like structure which connects the pharynx with the intestine.
4. Intestine:
Immediately after its origin, the intestine divides into two lateral branches which extend up to the posterior end of the body, where they end blindly. Each branch gives off many caecae or diverticulae on their either side. The outer diverticulae are large and branched but the inner diverticulae are small and un-branched.
Food, Feeding and Digestion:
Fasciola feeds on the cells, cell fragments, mucus, tissue fluids and blood of the host. The food is sucked by the muscular pharynx and pumped into the intestine. The intestine contains secretive and absorptive cells. Digestion is partly extracellular. The digested food is distributed to all parts of the body by numerous intestinal diverticula. The undigested waste diffuses out into the surrounding parenchyma.
Term Paper # 4. Respiration System of Fasciola Hepatica:
In the Fasciola the respiratory organs are absent so that the respiration takes place through general body surface by the process of diffusion. Since the animal is an endoparasite, the rate of respiration is very low and is anaerobic. In this process, there is no necessity of oxygen.
Glycogen undergoes anaerobic glycolysis to form pyruvic acid. Pyrubic acid is decarboxylated to form CO2 and an acetyl group. The latter combines with coenzymes to form acetyl co-enzyme A. Acetyl coenzyme A is finally condensed and reduced to form fatty acids. During the process energy is released.
Term Paper # 5. Excretory System of Fasciola Hepatica:
The excretory organs of Fasciola are extremely branched consists of flame cells and excretory ducts.
1. The Flame Cells or Protonephridia:
Flame cells or flame bulbs are modified irregular mesenchyme cells. These are distributed throughout mesenchyme in a specific pattern. Each sends out several pseudopodial processes in the surrounding mesenchyme. It has thin and elastic cell wall, peripheral cytoplasm and a central intracellular space or intracellular lumen. A bunch of long vibratile cilia flicker constantly like a flame inside the central space. It drives the excretory waste products collected from the parenchyma towards the excretory pore.
2. Excretory Ducts:
The main excretory canal is situated in the posterior ¾ of the body on the ventral side in the median line. It opens to the outside by an excretory pore, which is present on the ventral surface at the posterior end of the body. The dorsal and two ventral excretory ducts open into the main excretory canal at the anterior end.
Numerous lateral branches are given off on either side of these ducts throughout their length. These lateral branches are subdivided into fine capillaries. A flame cell is found at the end of each capillary.
Term Paper # 6. Nervous System of Fasciola Hepatica:
The nervous system is well developed in Fasciola.
It comprises of the following parts:
1. Brain consisting of a pair of cerebral ganglia and a ventral ganglion.
2. A nerve collar around the pharynx and connecting the cerebral ganglia and the ventral ganglion.
3. Nervous from the cerebral ganglia to the head lobe and to the hinder part of the body.
4. Three pairs of longitudinal nerve cords. A pair of thick lateral nerves extends to the posterior end of the body and a pair of thin dorsal and ventral nerves to the various organs of the viscera.
Term Paper # 7. Reproductive System in Fasciola Hepatica:
Fasciola is a hermaphrodite or bisexual animal. The male and female reproductive organ both are found in each adult animal but cross fertilization takes place in them.
The male reproductive system includes the following organs:
1. Testes
2. Vasa deferentia
3. Seminal vesicle
4. Ejaculatory duck
5. Cirrus and cirrus sac
6. Prostate glands
7. Genital atrium
1. Testes:
They are extremely branched, tubular structures which are situated one behind the other in the posterior half of the body.
2. Vasa Deferentia:
A narrow delicate was different arises from each testes and runs forward forming the common sperm duct just below the ventral sucker.
3. Seminal Vesicle:
The common sperm duct leads into a large muscular pear-shaped sac, the seminal vesicle, which lies in front of ventral sucker.
4. Ejaculatory Duct:
It arises as a fine convoluted tube from the seminal vesicle and runs forward in a zigzag fashion through the cirrus to open into the genital chamber through the male genital pore.
5. Cirrus and Cirrus Sac:
The cirrus is a muscular and cylindrical structure through the middle of which the ejaculatory duct passes. The cirrus can be everted out and down in through the genital pore. It is used during copulation to transfer the sperms into the other fluke. The cirrus and seminal vesicles are enclosed in a sac-like cirrus sac.
6. Prostate Glands:
Numerous unicellular prostate glands surround the ejaculatory duct and open into it. The alkaline prostatic secretion helps in the movement of sperms.
7. Genital Atrium:
The male and female genital pore both open into a small, common chamber called the genital atrium.
It opens to the outside by a gonopore situated in front of the acetabulum.
The following organs are found in the female reproductive system:
1. An ovary
2. An oviduct
3. An ootype
4. An uterus
5. Shell glands and their ducts
6. Vitelline glands and their ducts
7. Laurer’s canal.
1. Ovary:
It is a much branched, tubular structure which is situated in front of the testes on the right side in the anterior one third part of the body.
2. Oviduct:
A short, marrow and coiled tube called oviduct arises from the inner surface of the ovary. It extends ventrally and posteriorly to open into the uterus. The Laurer’s canal arises from the junction and the common vitelline duct opens into it.
3. Ootype:
The junction of the oviduct and the common vitelline duct is swollen to form the ootype which is surrounded by numerous Mehlis’s glands. The eggs are stored in the ootype. In Fasciola hepatica, however, an ootype is said to be absent.
4. Uterus:
The uterus arises from the ootype as a wide convoluted tube and runs forward to open into the genital atrium on the left side by the female genital pore. It is filled with fertilized eggs. The terminal part of uterus is muscular and helps in ejecting out the eggs.
5. Shell Glands:
They are also known Mehlis’s glands. They are numerous unicellular glands surrounding the ootype. Their secretion is stored in the ootype and collects around the eggs to form the shell. It lubricates the passage of the eggs to the uterus.
6. Vitelline Glands:
The vitelline glands extend along the lateral sides of the body from one end to the other in the form of innumerable, minute vesicles. A minute duct arises from each vesicle. These numerous ducts unite together and open into open the lateral longitudinal duct of their side. The lateral longitudinal duct of the two sides is connected with each other by transverse vitelline duct in the middle region of the body. A median vitelline duct arises from the middle of the transverse vitelline duct and joins the evident.
7. Laurer’s Canal:
The Laurer’s canal arises from the oviduct and acts as a sperm duct. It develops a temporary opening on the dorsal body surface during breeding season.
Term Paper # 8. Control of Fasciola Hepatica:
The disease may be controlled by two methods:
1. Therapy:
It involves treatment with drugs. The drugs generally employed as anthelmintics are Carbon tetrachloride.
Emetine hydrochloride, Filicin, Hexachloroethane and Tetrachlorethane, etc.
2. Prophylaxis:
The preventive measures include:
(i) Killing heavily infected sheep,
(ii) Destroying eggs and manure of infected sheep,
(iii) Feeding infected sheep with salt and little dry food, and
(iv) Killing the larval stages and snails which serve as intermediate host.
Snails are killed by sprinkling copper sulphate solution in ponds and ditches or by bluestone in one hundred thousand parts of water. The breeding of snails can be checked by removing the vegetation from the ponds and the streams. Ducks feed on snails and can be helpful in the reduction of the snail population.
Snails cannot survive longer periods of drying and can be killed by draining their pastures. Human infection could be checked by eating adequately-cooked and properly-washed vegetables and water plants.
Term Paper # 9. Parasitic Adaptations in Fasciola Hepatica:
Due to parasitic mode of life, Fasciola hepatica acquires certain modifications in morphology, anatomy, physiology, etc. These are called parasitic adaptations.
These may be discussed under the following heads:
A. Morphological Adaptations:
1. Body is leaf-like, dorso-ventrally flattened and oval.
2. Presence of two muscular sucker (oral and ventral) for the attachment to the tissues of the host.
3. Body is covered over with thick, resistant cuticle having backwardly directed spinules which prevent the parasite from slipping in the bile duct. Gastric juice has no effect on the cuticle.
4. Body is simple, not divided into head, trunk and tail, and has no appendages.
B. Anatomical Modifications:
1. The cilia are not found in the adult state but a thick layer of cuticle is present around the body so that it is not affected by the digestive juices of the host. Therefore, spines are also found on the body wall.
2. The cuticle thickens near the mouth and on the ventral surface to form two suckers.
3. The organs of locomotion are absent in the adult because it has no need to move about in the body of the host but cilia are present in the free living larva.
4. The digestive system is incomplete. The mouth is situated at the anterior end of the body. It is a terminal aperture and surrounded by a sucker. The pharynx is highly muscular and suctorial.
5. The intestine is highly branched so that the digested food can be distributed to different parts of the body. Therefore, it fills the absence of a circulatory system.
6. Being parasitic, it gets already digested food in large amount, therefore, the anal opening is absent.
7. The circulatory and respiratory system is absent. Anaerobic respiration takes place in it. This is very important for endoparasitic life because it is very difficult to get free oxygen in the body of the host.
8. The excretory organs are very well developed. It is a system of highly branched excretory canals at the ends of which flame cells are present.
9. The nervous system is less developed and the sense organs are entirely absent because the environmental changes do not take place in the body of the host.
10. The reproductive organs are highly developed. The gametes are formed by the highly branched ovaries and testes.
C. Physiological Adaptations:
1. The parasite is well adapted to the osmotic concentration of the bile in which it lives.
2. Respiration is anaerobic.
3. Can absorb certain amino-acids through its body wall.
4. Osmoregulation is not needed because the osmotic concentration of the body fluids of Fasciola is almost equal to that of the host’s bile.
D. Behavioural Adaptations:
Although hermaphrodite, cross fertilization takes place. During copulation both the mating partners are mutually and reciprocally used i.e. cirrus of one is inserted into the Laurer’s canal of the other ejecting the sperms. Thus, egg of partners get fertilized leading to a double rate of reproduction.
E. Adaptations in Life History:
1. The eggs are produced in a very large number so that they may be well distributed and some, not all, may develop further.
2. The egg is encapsulated. It is essential for their survival. In spite of this a large number of eggs perish due to non-availability of suitable environment.
3. Presence of a secondary mollusk host for the dispersal of the race.
4. Asexual multiplication of the larval forms (sporocysts, rediae and cercariae).
5. Miracidium is the first larval form which is ciliated and free swimming. It searches the new host (snail) for further development. The cercariae are free swimming and undergo encystment to avoid desiccation.