LECTURE NOTES ON FASCIOLA HEPATICA ( THE SHEEP LIVER FLUKE )

FASCIOLA HEPATICA ( THE SHEEP LIVER FLUKE )

Systematic position

PHYLUM-PLATYHELMINTHES

CLASS-TREMATODA

ORDER-DIGENEA

Distribution :It is distributed throughout the world. They cause liver rot disease in sheep.

Morphology: Its body is oval, dorsoventrally flat and looks like a leaf. Its body is soft and is 1.5 to 5 cm in length; 5 to 1.5 cm in width in the middle of the body. The body is pinkish in color. The digestive system is brownish colour because of the presence of ingested bile. At the anterior end mouth opening is present.On the ventral side above the ventral sucker a small genital openings is present. In the breeding season on the dorsal side a small opening of Laurer's canal is developed.At the posterior end a small excretory opening is present.At the anterior around the mouth an oral sucker is present. It is 1 mm. in diameter It is useful for ingestion and adhesion also.On the ventral side a ventral sucker is present 3 to 4 mm. away from anterior end. It is a large sucker. It is useul for adhesion.

T.S. of Body:

The body wall of Fasciola shows the following parts.

a) Tegument: It is an outer cytoplasmic layer. It shows microvilli. It is syncytial layer. It is thick. It contains mitochondria, endoplasmic reticulum etc. It contains sclero protein and is resistant to digestive juices. It shows backwardly directed spines.

b) Basement membrane: Below the tegument basement membrane is present.

c) Musculature: Below the basement membrane muscle layers are seen. The muscles are circular and longitudinal. Below the longitudinal muscles oblique muscles are also present.Below the muscles loose parenchymatous tissue is present. In this tissue various organs are enclosed. In this tissue, big mesenchyme cells are present. In this parenchyma all systems are included like digestive, excretory and nervous systems.

Digestive system: The digestive system is well developed.It distributes digested food to all parts of the body. At the anterior end of the body a mouth opening is present. It is surrounded by oral sucker. Mouth leads into buccal cavity, which leads into pharynx. Pharynx  is a thick chamber with glands. It leads into narrow oesophagus which  opens into intestine. This intestine is divided into branches. Each branch gives a number of irregular side branches. The two branches will end blindly near the posterior end of the animal. The intestine is lined by endoderm.These animals suck the tissue, fluid, lymph and bile from the host body. The digested food is distributed to all body parts of the branches of intestine. The tegument absorbs glucose from the host directly.

Excretory system : In liver fluke the excretion is carried on by flame cells. Liver fluke shows a big median longituidnal excretory canal with a number of branches and sub branches. The fine branches end with flame cells. These cells are hidden in the mesenchyme. The median longitudinal excretory canal opens at the posterior end through excretory opening.Each fell is irregular in shape. It is covered by thin wall. It produces branches which look like pseudopodia. The lumen of the cell is big and the nucleus is pushed to one side. In the lumen a group of flagella are present. They show movement. It looks like the flickering of a flame hence it is called flame cell.

From the mesenchyme the flame cells absorb the nitrogenous wastes and aminoacids. These wastes are pushed into the capillaries to which flame cells are connected. From there wastes enter into median longitudinal excretory canal and finally sent out through excretory pore.

Respiration:Fasciola hepatica lives in the bile duct of sheep as endoparasite. In this environment oxygen supply is very limited. Hence it takes up anaerobic respiration. The Carbon dioxide formed will be sent out through the body surface by diffusion.

Nervous system :The nervous system is well developed in Fasciola. On the dorsolateral sides of oesophagus two cerebral ganglia and a ventral ganglion are present. They are all united and a nerve ring is formed around the oesophagus.From the nerve ring 3 pairs of longitudinal nerve cords will arise. They are 1 pair on dorsal side,1 pair on ventral side and1 pair on lateral sides.The lateral longitudinal nerve cords are very long and well developed. They show transverse connectives. From the nerve ring and from all longitudinal nerve cords, fine nerves will go to all parts of the body.

Reproductive system:

Fasciola is a hermaphroditic or bisexual animal. It has both male and female reproductive organs.

a) Male reproductive system: The male reproductive system consists of a pair of a highly branched testis lying one above the other in the body. From each testis vas deferens arises. The two vas deferens or spermducts go forward and unite. The seminal vesicle is continued as an ejaculatory duct. It opens into the genital atrium which lies above the ventral sucker. The terminal part of the ejaculatory duct is highly muscular and known as the penis or cirrus. When not in use the cirrus is present in a sac called the cirrus sac.

b) Female reproductive system: The female reproductive system consists of a single highly branched ovary lying on the right side of the body. From the ovary oviduct arises which proceeds towards the centre of the body.On each side of the body two longitudinal vitelline ducts and a number of vitelline glands are present. They unite with longitudinal vitelline ducts through small ducts. The longitudinal ducts are connected by a transverse vitelline duct which is positioned a bit above the middle line of the body. From this transverse vitelline duct which is positioned a bit above the middle line of the body. From this transverse vitelline duct arises. This gives a median vitelline duct and it unites with oviduct. The combined duct opens into ootype. At the junction of the vitelline duct and oviduct a uterus arises. It is a long coiled tube. It opens into the genital atrium through female genital opening. At the junction of uterus, oviduct and vitelline duct, mehlis glands are present. The junction of the three ducts is called Ootype.During breeding season from this junction a temporary canal arises called Laurer's canal. It opens on the dorsal side of the body.