Fasciola Hepatica – The Liver Fluke


Fasciolahepatica is a common fluke found in the liver and bile ducts of cattle, sheep, goat, pig, rabbit, dog etc. It causes damage to the liver tissues producing liver rot in all sheep breeding areas of the world. Its life cycle is completed in two hosts, a vertebrate, the sheep and an invertebrate host, which is the snail of the genera Planorbis, Limnaea and Bulinus.

MORPHOLOGY

Fasciola is a flattened, pinkish, leaf-like and bilaterally symmetrical animals, about 25-30 mm in length and somewhat rounded on anterior side into a conical projection and posterior end is pointed to form the oral cone or head lobe, bearing at its tip a mouth.

There are two cup-like suckers, an oral sucker on the anterior end around the mouth and a large ventral sucker or acetabulum on the ventral side for attachment to the host by producing vacuum. The genital aperture or gonopore is situated on the anterior side of the ventral side. At the posterior end of the body there is an excretory pore for excretion of nitrogenous wastes. Body is covered with tegument containing numerous minute backwardly directed spinules or scales, which anchor the body and help in moving within narrow spaces in liver.

ANATOMY

SKIN

A tough resistant tegument or cuticle, made of scleroprotein covers the fluke body and protects it from the digestive juices of the host. It bears small backwardly directed spinules or scales. The lowest layer of the cuticle forms a delicate basement membrane. The integumentary muscles include an outer circular layer and an inner longitudinal layer and oblique or diagonal muscles. All muscle fibres are smooth. Mesoderm constitutes

 uninucleate and binucleate cells with syncytial network filled with cytoplasm. Skin provides protection, it is the site of gaseous exchange and various nitrogenous wastes are diffused out through it. It also helps in the absorption of nutrients particularly glucose from the host.

DIGESTIVE SYSTEM

Fasciolahepatica has a blind sac alimentary canal with mouth as the only opening situated in the middle of anterior sucker. Mouth opens into bulb-like pharynx which is muscular and suctorial. The intestine is bifurcated into two caeca and gives off numerous branches or diverticula in order to carry food to all parts of the body. Therefore, digestive system also functions as circulatory system.

Fasciola feeds on bile, blood and lymph and cellular debris. Digestion is extracellular and occurs in intestine and the digested food is accomplished by ramifying diverticula of intestine. Reserve food in the form of glycogen and fats is stored in the parenchyma. The undigested food is ejected through the mouth.

Mode of respiration is anaerobic as there is no fr

RESPIRATORY SYSTEM

ee oxygen in liver. Glycogen is metabolized to carbon dioxide and fatty acids by way of glycolysis releasing energy.

Pyruvic acid is decarboxylated to form carbon dioxide and an acetyl group. The carbon dioxide is diffused out through the general body surface and fatty acids are excreted through excretory system.

EXCRETORY SYSTEM

The excretory system is concerned with excretion as well as osmoregulation. It consists of Flamecells, which are modified mesenchyme cells of irregular shape and send out pseudopodial processes into the surrounding tissue.

 Excretory products from flame cells are collected by capillaries that join into the intracellular cavity of flame cells. The capillaries anastomose and open into the excretory ducts which eventually join the median longitudinal excretory canal. The longitudinal excretory canal is non-ciliated but the capillaries and ducts are lined with cilia.

The excretory wastes, which are fatty acids and ammonia, diffuse from the surrounding mesenchyme into the flame cells and finally collected by their intracellular cavities. The cilia cause the flow of wastes from cavities into the excretory ducts and then into main excretory canal and finally to the exterior through excretory pore.

NERVOUS SYSTEM & SENSE ORGANS

It consists of a pair of cerebral ganglia situated on either side of oesophagus. The ganglia are joined together by a cerebral ring around the oesophagus. From the nerve ganglia nerves are given off to the head lobe and to the posterior part of the body. Three pairs of longitudinal nerve cords extend to the posterior side and give out numerous fine peripheral branches to various organs. Of these, one pair is dorsal, one ventral, and one lateral. 

Adult Flukes lack any sense organs.

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